CA1177704A - Optical coatings for high temperature applications - Google Patents
Optical coatings for high temperature applicationsInfo
- Publication number
- CA1177704A CA1177704A CA000407537A CA407537A CA1177704A CA 1177704 A CA1177704 A CA 1177704A CA 000407537 A CA000407537 A CA 000407537A CA 407537 A CA407537 A CA 407537A CA 1177704 A CA1177704 A CA 1177704A
- Authority
- CA
- Canada
- Prior art keywords
- filter
- lamp
- visible light
- envelope
- radiation
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 238000000576 coating method Methods 0.000 title claims abstract description 80
- 230000003287 optical effect Effects 0.000 title claims abstract description 73
- 239000011248 coating agent Substances 0.000 claims abstract description 68
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 55
- 229910052736 halogen Inorganic materials 0.000 claims abstract description 34
- 150000002367 halogens Chemical class 0.000 claims abstract description 34
- 235000012239 silicon dioxide Nutrition 0.000 claims abstract description 28
- 239000000377 silicon dioxide Substances 0.000 claims abstract description 22
- 239000000758 substrate Substances 0.000 claims abstract description 22
- 239000000463 material Substances 0.000 claims abstract description 21
- BPUBBGLMJRNUCC-UHFFFAOYSA-N oxygen(2-);tantalum(5+) Chemical compound [O-2].[O-2].[O-2].[O-2].[O-2].[Ta+5].[Ta+5] BPUBBGLMJRNUCC-UHFFFAOYSA-N 0.000 claims abstract description 20
- PBCFLUZVCVVTBY-UHFFFAOYSA-N tantalum pentoxide Inorganic materials O=[Ta](=O)O[Ta](=O)=O PBCFLUZVCVVTBY-UHFFFAOYSA-N 0.000 claims abstract description 20
- 239000005350 fused silica glass Substances 0.000 claims abstract description 4
- 230000005855 radiation Effects 0.000 claims description 24
- 238000002834 transmittance Methods 0.000 claims description 16
- 230000003595 spectral effect Effects 0.000 claims description 14
- 238000001228 spectrum Methods 0.000 claims description 14
- 238000000151 deposition Methods 0.000 claims description 8
- 238000000149 argon plasma sintering Methods 0.000 claims description 6
- 239000012780 transparent material Substances 0.000 claims description 3
- 230000008018 melting Effects 0.000 claims description 2
- 238000002844 melting Methods 0.000 claims description 2
- 229910052751 metal Inorganic materials 0.000 claims description 2
- 239000002184 metal Substances 0.000 claims description 2
- 229960001866 silicon dioxide Drugs 0.000 description 16
- 230000006872 improvement Effects 0.000 description 9
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 7
- 239000010453 quartz Substances 0.000 description 6
- 239000010409 thin film Substances 0.000 description 6
- 239000007789 gas Substances 0.000 description 5
- 229910052721 tungsten Inorganic materials 0.000 description 5
- 239000010937 tungsten Substances 0.000 description 5
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 4
- 230000008021 deposition Effects 0.000 description 4
- 238000010438 heat treatment Methods 0.000 description 4
- 206010037660 Pyrexia Diseases 0.000 description 3
- 230000005670 electromagnetic radiation Effects 0.000 description 3
- 229910044991 metal oxide Inorganic materials 0.000 description 3
- 150000004706 metal oxides Chemical class 0.000 description 3
- 238000007789 sealing Methods 0.000 description 3
- 238000010521 absorption reaction Methods 0.000 description 2
- 239000010408 film Substances 0.000 description 2
- 238000005086 pumping Methods 0.000 description 2
- 230000004044 response Effects 0.000 description 2
- 239000010979 ruby Substances 0.000 description 2
- 229910001750 ruby Inorganic materials 0.000 description 2
- 239000004408 titanium dioxide Substances 0.000 description 2
- 238000001771 vacuum deposition Methods 0.000 description 2
- PFNQVRZLDWYSCW-UHFFFAOYSA-N (fluoren-9-ylideneamino) n-naphthalen-1-ylcarbamate Chemical compound C12=CC=CC=C2C2=CC=CC=C2C1=NOC(=O)NC1=CC=CC2=CC=CC=C12 PFNQVRZLDWYSCW-UHFFFAOYSA-N 0.000 description 1
- 239000005083 Zinc sulfide Substances 0.000 description 1
- 239000006096 absorbing agent Substances 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 230000000740 bleeding effect Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 230000007123 defense Effects 0.000 description 1
- 238000005137 deposition process Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000010891 electric arc Methods 0.000 description 1
- 238000005566 electron beam evaporation Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000008020 evaporation Effects 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 238000009501 film coating Methods 0.000 description 1
- 239000003574 free electron Substances 0.000 description 1
- 230000014509 gene expression Effects 0.000 description 1
- 238000005286 illumination Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- SOQBVABWOPYFQZ-UHFFFAOYSA-N oxygen(2-);titanium(4+) Chemical compound [O-2].[O-2].[Ti+4] SOQBVABWOPYFQZ-UHFFFAOYSA-N 0.000 description 1
- 238000001429 visible spectrum Methods 0.000 description 1
- 229910052984 zinc sulfide Inorganic materials 0.000 description 1
- DRDVZXDWVBGGMH-UHFFFAOYSA-N zinc;sulfide Chemical compound [S-2].[Zn+2] DRDVZXDWVBGGMH-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01K—ELECTRIC INCANDESCENT LAMPS
- H01K1/00—Details
- H01K1/28—Envelopes; Vessels
- H01K1/32—Envelopes; Vessels provided with coatings on the walls; Vessels or coatings thereon characterised by the material thereof
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/20—Filters
- G02B5/28—Interference filters
- G02B5/281—Interference filters designed for the infrared light
- G02B5/282—Interference filters designed for the infrared light reflecting for infrared and transparent for visible light, e.g. heat reflectors, laser protection
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Optical Filters (AREA)
- Surface Treatment Of Optical Elements (AREA)
- Surface Treatment Of Glass (AREA)
- Optical Elements Other Than Lenses (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A coated article useful in high temperature environments substantially in excess of 500°C comprising a substantially transparent substrate formed of a material adapted to with-stand said high temperature environment and an optical coat-ing formed on one surface of said substrate and comprising a first set of layers consisting at least primarily of silicon dioxide and a second set of layers consisting at least pri-marily of tantalum pentoxide. The optical coating comprises an interference filter formed of alternating layers of fused silica and tantalum pentoxide. A halogen cycle lamp with visible light transmitting, IR reflecting filter formed on the outside surface of the lamp envelope improves energy efficiency by at least twenty-five percent.
A coated article useful in high temperature environments substantially in excess of 500°C comprising a substantially transparent substrate formed of a material adapted to with-stand said high temperature environment and an optical coat-ing formed on one surface of said substrate and comprising a first set of layers consisting at least primarily of silicon dioxide and a second set of layers consisting at least pri-marily of tantalum pentoxide. The optical coating comprises an interference filter formed of alternating layers of fused silica and tantalum pentoxide. A halogen cycle lamp with visible light transmitting, IR reflecting filter formed on the outside surface of the lamp envelope improves energy efficiency by at least twenty-five percent.
Description
~.'17~77~
OPTICAL COATINGS FOR HIGH TEMPERATURE APPLICATIONS
This invention relates generally to optical coatings and specifically to optical coatings for high temperature appli-cations. More specifically, this invention relates to hightemperature, energy saving lamps with an optical coating thereon to improve energy efficiency.
Thin film optical coatings of the interference filter type which utilize two materials of different indices of refrac-tion have not generally been applied in high temperature en-vironments in which the coatings are exposed to the air at temperatures in excess of 500C for many hours. Typically thin film optical coatings do not survive these operating environments, failure being due to one of the following:
loss of adhesion of the optical coating to the substrate, interdiffusion of the materials of the high and low refrac-tive index layers of the coating, decrease in the index ratio of the two materials, evaporation of the thin film layers, or unacceptable increases in the absorption of the coating.
One application in which thin film optical coatings are use-ful is to improve the illumination efficiency of incandescent ~5 lamps. It is well-known that applying a hot mirror type of optical coating to the envelope of an incandescent lamp in-creases its energy efficiency. The hot mirror reflects infrared energy emitted by the filament back to the filament while transmitting the visible light portion of the electro-magnetic spectrum emitted by the filament. This lowers the ~ 7~
amount of electrical energy required to be supplied to thefilament to maintain its operating temperature. For example, U. S. Patent 3,949,259, 4,017,758, 4,127,789, 4,160,929, and 4,227,113 disclose the use of various types of hot mirrors on all or portions of an incandescent lamp envelope. How-ever, none of these references discloses specific applica-tions in which the optical coating is formed on a lamp envelope surface which operates in air at a temperature sub-stantially in excess of 500C.
U. S. Patent 4,017,758 teaches the use of a hot mirror opti-cal coating consisting of a composite of a heavily doped metal oxide filter formed nearest the filament body of the lamp and a multilayer interference filter disposed either adjacent to the heavily doped metal oxide filter or on a dif-ferent surface of the lamp envelope. For example, the '758 patent suggests that both filters may be disposed on the in-side wall of the lamp envelope or both on the outside wall or one component on the inside and the other on the outside wall surface, respectively. The '758 patent also discloses a special lamp embodiment utilizing a double wall lamp envelope and suggests various combinations which may be employed for disposing the interference filter and the doped metal oxide filter on lamp envelope walls in such an embodiment. Al-though the '758 patent makes specific reference to use of thecomposite filters disclosed therein in halogen lamps, the reference does not disclose any example of interference filter materials which could survive the operating tempera-tures of the surface of the lamp envelope of a halogen lamp.
The only high refractive index materials referred to in the '758 patent are zinc selenide, zinc sulfide, and titanium di-oxide. Thus, while the '758 patent refers to the use of silicon dioxide as the low refractive index layer in an interference coating (and it is well-known that silicon di-oxide will survive in a high temperature environment) thehigh refractive index materials referred to in the '758 patent will not survive the high temperature environment of ~7~7704 about 800C on the outside surface of the envelope of a halogen lamp.
Accordingly, it is the principal object of this invention to provide an optical coating comprising layers of low and high refractive index materials which will withstand a high temp-erature environment in excess of 500C.
It is another object of this invention to provide a multi-layer optical interference filter which is capable of with-standing a high temperature environment.
It is another object of this invention to provide a hot mir-ror optical coating which may be utilized in a high tempera-ture environment.
It is a further object of this invention to provide a halogencycle lamp envelope with an optical interference filter form-ed on the outer surface thereof which will survive the oper-ating temperature of the lamp envelope.
It is a further object of this invention to provide a halogenlamp with an energy saving optical interference filter formed on an outer surface of the lamp envelope.
This invention is based on the discovery that an optical coating which comprises a first set of layers consisting at least primarily of silicon dioxide and a second set of layers consisting at least primarily of tantalum pentoxide will sur-vive a high temperature environment even where the opticalcoating is operated at the high temperature environment in air for a substantial period of time. Many other optical coating combinations with silicon dioxide as the low refractive index material and other refractory-type high refractive index materials such as titanium dioxide will not survive similar high temperature operating environments.
It has also been discovered that optical coatings in accor-11777C~4 --4--dance with this invention will survive the high temperature environment of the outside surface of a halogen lamp envelope having a small radius of curvature, since a small curvature accentuates problems of coating stresses due to thermal mis-matches.
Accordingly, one aspect of this invention features a coatedarticle useful in high temperature environments substantially in excess of 500C where the article comprises a substantial-ly transparent substrate formed of a material adapted towithstand a high temperature environment and an optical coat-ing formed on one surface of the substrate and comprising a first set of layers consisting at least primarily of silicon dioxide and a second set of layers consisting at least pri-marily of tantalum pentoxide. The optical coating may, forexample, comprise an interference filter formed of alternat-ing layers of these first and second sets thereof. The interference filter may comprise a bandpass filter designed to transmit radiation in a preselected first wavelength band and to reflect radiation in adjacent wavelength region. A
specific example of such a bandpass filter is a hot mirror having high transmittance for visible light and high infrared reflectance. Alternatively, the bandpass filter may be a color filter having a high transmittance for a preselected portion of the visible light spectrum and high reflectance for adjacent spectral regions. The substrate on which the optical coating is formed may comprise a fused quartz lamp envelope adapted to be utilized in a halogen cycle incandes-cent lamp operating at an outer envelope surface temperature of at least about 800C with the interference filter formed on the outer surface of the lamp envelope.
In accordance with another aspect of this invention, a coated article is provided which is useful in high temperature envi-ronments substantially in excess of 500C and comprises asubstantially transparent substrate formed of a material adapted to withstand the high temperature environment and an optical coating formed on one surface of the substrate and comprising a multilayer interference filter having high re-flectance of infrared radiation and high scattering of vis-ible light. This interference filter is formed by deposit-ing on the substrate a multilayer dielectric stack composedof alternate layers consisting at least primarily of silicon dioxide and tantalum pentoxide and then baking the coated substrate in air at a temperature of at least about 1100C.
In accordance with another aspect of this invention an im-proved energy efficient halogen lamp is provided. The halo-gen lamp comprises a lamp envelope having a geometry which has an internal focal point, line or plane and formed of a substantially transparent material capable of withstanding operating temperatures of at least 800C. A high melting point metal filament is mounted within the lamp envelope sub-stantially at the focal point, line or plane and a halogen gas is provided to fill the envelope. An interference filter is formed on an outer surface of the lamp envelope and is comprised of alternate layers consisting at least primari-ly of silicon dioxide and tantalum pentoxide, respectively.
The interference filter formed on the halogen lamp may be a bandpass filter having high transmittance for visible light and high reflectance of infrared radiation. Alternatively, the interference filter may comprise a bandpass filter having high transmittance radiation in a preselected portion of the visible light spectrum and high reflectance of radiation in adjacent wavelength regimes to produce a lamp which has a light output of a preselected color.
The interference filter formed on the halogen lamp may also comprise a visible light scattering, infrared reflecting filter formed by depositing on the outer surface of the lamp envelope a multilayer dielectric stack of the primarily sili-con dioxide and tantalum pentoxide layers having a high transmittance of visible light and high infrared reflectance 1~L77~7~9~
and then baking the envelope and filter in air at a tempera-ture of at least about 1100C to convert the filter from a visible light transmitting filter to a substantially visible light scattering filter.
The halogen lamp in accordance with this invention may also utilize a multilayer interference filter formed on substrates utilized as end reflectors in the lamp envelope.
This invention enables for the first time improvements in energy efficiency to be applied in an optimal fashion to halogen cycle lamps by enabling the formation of an optical interference coating directly on the outside surface of the halogen lamp envelope which generally operates at a tempera-ture of about 800C. Improvements in performance in therange of about twenty-five to thirty percent have been mea-sured in 1500 watt halogen cycle lamps to which the invention has been applied. This level of improvement would not be practicably achieved if the IR reflecting coating were placed on a separate surface surrounding and spaced from the outer surface of the lamp envelope to reduce the operating tempera-ture of the coating.
The optical coatings of this invention may also find useful application in a wide variety of other high temperature envi-ronments such as heat reflecting windows for furnaces, laser pump lamps, and discharge lamps such as arc lamps utilized in theater projection equipment and the like. Generally the invention is applicable to providing optical coatings for use in any high temperature environment in which optical inter-ference filter type of optical coating performance will pro-vide an improvement in operating efficiency or other operat-ing aspects of the apparatus on which the coating is employed.
Other objects, features, and advantages of this invention will be apparent from a consideration of the following de-tailed description taken in conjunction with the accompanyingdrawings.
Fig. 1 is a partly sectioned elevational view of a halogen lamp incorporating an optical coating in accordance with this invention.
Fig. 2 is a fragmented elevational view of a hot mirror coat-ing design utilizing the principles of this invention.
Fig. 3 is a graph illustrating the spectral emission of a black body.
Fig. 4 is a graph showiny the visible transmittance and in-frared reflectance characteristics of an exemplary optical coating in accordance with this invention.
Fig. 5 is a graph of the spectral reflectance of a shortwave pass dielectric stack component of the overall optical coat-ing illustrated in Fig. 2.
Fig. 6 is a graph of the spectral reflectance of a 2:1 di-electric stack employed as one component of the optical coat-ing depicted in Fig. 2.
Fig. 7 is a graph of the spectral reflectance of another shortwave pass dielectric stack used as one component of the optical coating depicted in Fig. 2.
Fig. ~ is a graph of the spectral transmittance, reflectance, and scatter response of a visible light scattering, infrared reflecting optical coating in accordance with this invention.
Referring now to Fig. 1, the principles of this invention will be set forth in their application to a halogen cycle tungsten lamp 10. It should be understood, however, that the principles of the invention are applicable to any high 1~7t7704 temperature environment in which an optical coating may find utility. The halogen cycle lamp 10 comprises a lamp envelope 11 which includes a fused quartz tube 12 and a pair of end sealing and mounting structures 13. Along the central axis of the quartz tube 12 a coiled tungsten filament 15 is sup-ported by a plurality of support structures 16. End reflec-tors 17 may be provided at the ends of the tungsten filament 15. In the manufacturing process, the halogen cycle lamp is formed by sealing the tube 12 using the sealing end sections 13 and then evacuating the tube 12 and refilling it with an appropriate reactive halogen atmosphere.
During operation of the halogen lamp 10, the halogen gas re-acts with tungsten which has evaporated from the filament.
The resulting gas is chemically decomposed at the hot surface of the tungsten filament so that the tungsten atoms therein are deposited on the filament and the halogen is freed to scavenge additional liberated tungsten atoms. In order for the halogen cycle lamp to operate properly, the quartz tube 12 must be maintained at a high temperature in the vicinity of about 8~0C and generally this is accomplished by keeping the diameter of the quartz tube 12 relatively small. For example, a typical lamp may be about ten inches long and about three-eights inch in diameter.
In accordance with this invention an optical coating 14 is deposited on the outer surface of the quartz tube 12. This optical coating comprises a first set of layers consisting at least primarily of silicon dioxide and a second set of layers consisting at least primarily of tantalum pentoxide. The design of optical coating 14 may take one of a number of forms depending on the spectral performance which is desired for the coating. Generally, the optical coating 14 will com-prise one or more dielectric stacks in which alternating layers of silicon dioxide and tantalum pentoxide are formed to produce an interference filter.
~1'7'~704 For convenience the optical filter layers will be referred to as layers of silicon dioxide and tantalum pentoxide, but it should be understood that the silicon dioxide layers may not consist solely of silicon dioxide and the tantalum pentoxide layers may not consist solely of tantalum pen-toxide. In each instance some amounts of other dielectric film constituents may be present~ For example, the tantalum pentoxide may also contain a small percentage of another refractory oxide such as titanium dioxide. It should also be understood that the optical filter 14 may take one of several forms, each of which embodies the general principle that it is a selectively reflecting coating, i.e. it is sub-stantially transparent to radiation in spectral regions in which it is desirable that the lamp 10 emit radiation and is substantially reflecting over the remainder of the spectrum of substantial emission of electromagnetic radiation by the hot filament. By reflecting back to the hot filament, radia-tion which is not desired to be emitted from the lamp con-serves the energy otherwise required to maintain the filament at operating temperature and thus reduces overall energy re-quirements for operating the lamp.
One of the alternative forms which optical coating 14 may take is the coating design 14A depicted in Fig. 2 and having the design parameters set forth in Table 1 below. The over-all performance of the coating is depicted in Fig. 4. As shown by the dashed curve 22, the coating 14A has high trans-mittance in the visible region of ~he electromagnetic radia-tion spectrum ~etween 400 nanometers and 700 nanometers and has a high reflectance throughout the remainder of the spec-trum, principally the near infrared where there is substan-tial emission of electromagnetic radiation by the hot fila-ment of the lamp, as shown by the curve 21 in Fig. 4.
Fig. 3 illustrates the radiant power spectrum from a 3,000 ~elvin black body and shows that only a small percentage of 77U~
LAYER INDEX OFTHICKNESS (nm) QWOT*
5 Air 1.000 1 1.45894.28 550
OPTICAL COATINGS FOR HIGH TEMPERATURE APPLICATIONS
This invention relates generally to optical coatings and specifically to optical coatings for high temperature appli-cations. More specifically, this invention relates to hightemperature, energy saving lamps with an optical coating thereon to improve energy efficiency.
Thin film optical coatings of the interference filter type which utilize two materials of different indices of refrac-tion have not generally been applied in high temperature en-vironments in which the coatings are exposed to the air at temperatures in excess of 500C for many hours. Typically thin film optical coatings do not survive these operating environments, failure being due to one of the following:
loss of adhesion of the optical coating to the substrate, interdiffusion of the materials of the high and low refrac-tive index layers of the coating, decrease in the index ratio of the two materials, evaporation of the thin film layers, or unacceptable increases in the absorption of the coating.
One application in which thin film optical coatings are use-ful is to improve the illumination efficiency of incandescent ~5 lamps. It is well-known that applying a hot mirror type of optical coating to the envelope of an incandescent lamp in-creases its energy efficiency. The hot mirror reflects infrared energy emitted by the filament back to the filament while transmitting the visible light portion of the electro-magnetic spectrum emitted by the filament. This lowers the ~ 7~
amount of electrical energy required to be supplied to thefilament to maintain its operating temperature. For example, U. S. Patent 3,949,259, 4,017,758, 4,127,789, 4,160,929, and 4,227,113 disclose the use of various types of hot mirrors on all or portions of an incandescent lamp envelope. How-ever, none of these references discloses specific applica-tions in which the optical coating is formed on a lamp envelope surface which operates in air at a temperature sub-stantially in excess of 500C.
U. S. Patent 4,017,758 teaches the use of a hot mirror opti-cal coating consisting of a composite of a heavily doped metal oxide filter formed nearest the filament body of the lamp and a multilayer interference filter disposed either adjacent to the heavily doped metal oxide filter or on a dif-ferent surface of the lamp envelope. For example, the '758 patent suggests that both filters may be disposed on the in-side wall of the lamp envelope or both on the outside wall or one component on the inside and the other on the outside wall surface, respectively. The '758 patent also discloses a special lamp embodiment utilizing a double wall lamp envelope and suggests various combinations which may be employed for disposing the interference filter and the doped metal oxide filter on lamp envelope walls in such an embodiment. Al-though the '758 patent makes specific reference to use of thecomposite filters disclosed therein in halogen lamps, the reference does not disclose any example of interference filter materials which could survive the operating tempera-tures of the surface of the lamp envelope of a halogen lamp.
The only high refractive index materials referred to in the '758 patent are zinc selenide, zinc sulfide, and titanium di-oxide. Thus, while the '758 patent refers to the use of silicon dioxide as the low refractive index layer in an interference coating (and it is well-known that silicon di-oxide will survive in a high temperature environment) thehigh refractive index materials referred to in the '758 patent will not survive the high temperature environment of ~7~7704 about 800C on the outside surface of the envelope of a halogen lamp.
Accordingly, it is the principal object of this invention to provide an optical coating comprising layers of low and high refractive index materials which will withstand a high temp-erature environment in excess of 500C.
It is another object of this invention to provide a multi-layer optical interference filter which is capable of with-standing a high temperature environment.
It is another object of this invention to provide a hot mir-ror optical coating which may be utilized in a high tempera-ture environment.
It is a further object of this invention to provide a halogencycle lamp envelope with an optical interference filter form-ed on the outer surface thereof which will survive the oper-ating temperature of the lamp envelope.
It is a further object of this invention to provide a halogenlamp with an energy saving optical interference filter formed on an outer surface of the lamp envelope.
This invention is based on the discovery that an optical coating which comprises a first set of layers consisting at least primarily of silicon dioxide and a second set of layers consisting at least primarily of tantalum pentoxide will sur-vive a high temperature environment even where the opticalcoating is operated at the high temperature environment in air for a substantial period of time. Many other optical coating combinations with silicon dioxide as the low refractive index material and other refractory-type high refractive index materials such as titanium dioxide will not survive similar high temperature operating environments.
It has also been discovered that optical coatings in accor-11777C~4 --4--dance with this invention will survive the high temperature environment of the outside surface of a halogen lamp envelope having a small radius of curvature, since a small curvature accentuates problems of coating stresses due to thermal mis-matches.
Accordingly, one aspect of this invention features a coatedarticle useful in high temperature environments substantially in excess of 500C where the article comprises a substantial-ly transparent substrate formed of a material adapted towithstand a high temperature environment and an optical coat-ing formed on one surface of the substrate and comprising a first set of layers consisting at least primarily of silicon dioxide and a second set of layers consisting at least pri-marily of tantalum pentoxide. The optical coating may, forexample, comprise an interference filter formed of alternat-ing layers of these first and second sets thereof. The interference filter may comprise a bandpass filter designed to transmit radiation in a preselected first wavelength band and to reflect radiation in adjacent wavelength region. A
specific example of such a bandpass filter is a hot mirror having high transmittance for visible light and high infrared reflectance. Alternatively, the bandpass filter may be a color filter having a high transmittance for a preselected portion of the visible light spectrum and high reflectance for adjacent spectral regions. The substrate on which the optical coating is formed may comprise a fused quartz lamp envelope adapted to be utilized in a halogen cycle incandes-cent lamp operating at an outer envelope surface temperature of at least about 800C with the interference filter formed on the outer surface of the lamp envelope.
In accordance with another aspect of this invention, a coated article is provided which is useful in high temperature envi-ronments substantially in excess of 500C and comprises asubstantially transparent substrate formed of a material adapted to withstand the high temperature environment and an optical coating formed on one surface of the substrate and comprising a multilayer interference filter having high re-flectance of infrared radiation and high scattering of vis-ible light. This interference filter is formed by deposit-ing on the substrate a multilayer dielectric stack composedof alternate layers consisting at least primarily of silicon dioxide and tantalum pentoxide and then baking the coated substrate in air at a temperature of at least about 1100C.
In accordance with another aspect of this invention an im-proved energy efficient halogen lamp is provided. The halo-gen lamp comprises a lamp envelope having a geometry which has an internal focal point, line or plane and formed of a substantially transparent material capable of withstanding operating temperatures of at least 800C. A high melting point metal filament is mounted within the lamp envelope sub-stantially at the focal point, line or plane and a halogen gas is provided to fill the envelope. An interference filter is formed on an outer surface of the lamp envelope and is comprised of alternate layers consisting at least primari-ly of silicon dioxide and tantalum pentoxide, respectively.
The interference filter formed on the halogen lamp may be a bandpass filter having high transmittance for visible light and high reflectance of infrared radiation. Alternatively, the interference filter may comprise a bandpass filter having high transmittance radiation in a preselected portion of the visible light spectrum and high reflectance of radiation in adjacent wavelength regimes to produce a lamp which has a light output of a preselected color.
The interference filter formed on the halogen lamp may also comprise a visible light scattering, infrared reflecting filter formed by depositing on the outer surface of the lamp envelope a multilayer dielectric stack of the primarily sili-con dioxide and tantalum pentoxide layers having a high transmittance of visible light and high infrared reflectance 1~L77~7~9~
and then baking the envelope and filter in air at a tempera-ture of at least about 1100C to convert the filter from a visible light transmitting filter to a substantially visible light scattering filter.
The halogen lamp in accordance with this invention may also utilize a multilayer interference filter formed on substrates utilized as end reflectors in the lamp envelope.
This invention enables for the first time improvements in energy efficiency to be applied in an optimal fashion to halogen cycle lamps by enabling the formation of an optical interference coating directly on the outside surface of the halogen lamp envelope which generally operates at a tempera-ture of about 800C. Improvements in performance in therange of about twenty-five to thirty percent have been mea-sured in 1500 watt halogen cycle lamps to which the invention has been applied. This level of improvement would not be practicably achieved if the IR reflecting coating were placed on a separate surface surrounding and spaced from the outer surface of the lamp envelope to reduce the operating tempera-ture of the coating.
The optical coatings of this invention may also find useful application in a wide variety of other high temperature envi-ronments such as heat reflecting windows for furnaces, laser pump lamps, and discharge lamps such as arc lamps utilized in theater projection equipment and the like. Generally the invention is applicable to providing optical coatings for use in any high temperature environment in which optical inter-ference filter type of optical coating performance will pro-vide an improvement in operating efficiency or other operat-ing aspects of the apparatus on which the coating is employed.
Other objects, features, and advantages of this invention will be apparent from a consideration of the following de-tailed description taken in conjunction with the accompanyingdrawings.
Fig. 1 is a partly sectioned elevational view of a halogen lamp incorporating an optical coating in accordance with this invention.
Fig. 2 is a fragmented elevational view of a hot mirror coat-ing design utilizing the principles of this invention.
Fig. 3 is a graph illustrating the spectral emission of a black body.
Fig. 4 is a graph showiny the visible transmittance and in-frared reflectance characteristics of an exemplary optical coating in accordance with this invention.
Fig. 5 is a graph of the spectral reflectance of a shortwave pass dielectric stack component of the overall optical coat-ing illustrated in Fig. 2.
Fig. 6 is a graph of the spectral reflectance of a 2:1 di-electric stack employed as one component of the optical coat-ing depicted in Fig. 2.
Fig. 7 is a graph of the spectral reflectance of another shortwave pass dielectric stack used as one component of the optical coating depicted in Fig. 2.
Fig. ~ is a graph of the spectral transmittance, reflectance, and scatter response of a visible light scattering, infrared reflecting optical coating in accordance with this invention.
Referring now to Fig. 1, the principles of this invention will be set forth in their application to a halogen cycle tungsten lamp 10. It should be understood, however, that the principles of the invention are applicable to any high 1~7t7704 temperature environment in which an optical coating may find utility. The halogen cycle lamp 10 comprises a lamp envelope 11 which includes a fused quartz tube 12 and a pair of end sealing and mounting structures 13. Along the central axis of the quartz tube 12 a coiled tungsten filament 15 is sup-ported by a plurality of support structures 16. End reflec-tors 17 may be provided at the ends of the tungsten filament 15. In the manufacturing process, the halogen cycle lamp is formed by sealing the tube 12 using the sealing end sections 13 and then evacuating the tube 12 and refilling it with an appropriate reactive halogen atmosphere.
During operation of the halogen lamp 10, the halogen gas re-acts with tungsten which has evaporated from the filament.
The resulting gas is chemically decomposed at the hot surface of the tungsten filament so that the tungsten atoms therein are deposited on the filament and the halogen is freed to scavenge additional liberated tungsten atoms. In order for the halogen cycle lamp to operate properly, the quartz tube 12 must be maintained at a high temperature in the vicinity of about 8~0C and generally this is accomplished by keeping the diameter of the quartz tube 12 relatively small. For example, a typical lamp may be about ten inches long and about three-eights inch in diameter.
In accordance with this invention an optical coating 14 is deposited on the outer surface of the quartz tube 12. This optical coating comprises a first set of layers consisting at least primarily of silicon dioxide and a second set of layers consisting at least primarily of tantalum pentoxide. The design of optical coating 14 may take one of a number of forms depending on the spectral performance which is desired for the coating. Generally, the optical coating 14 will com-prise one or more dielectric stacks in which alternating layers of silicon dioxide and tantalum pentoxide are formed to produce an interference filter.
~1'7'~704 For convenience the optical filter layers will be referred to as layers of silicon dioxide and tantalum pentoxide, but it should be understood that the silicon dioxide layers may not consist solely of silicon dioxide and the tantalum pentoxide layers may not consist solely of tantalum pen-toxide. In each instance some amounts of other dielectric film constituents may be present~ For example, the tantalum pentoxide may also contain a small percentage of another refractory oxide such as titanium dioxide. It should also be understood that the optical filter 14 may take one of several forms, each of which embodies the general principle that it is a selectively reflecting coating, i.e. it is sub-stantially transparent to radiation in spectral regions in which it is desirable that the lamp 10 emit radiation and is substantially reflecting over the remainder of the spectrum of substantial emission of electromagnetic radiation by the hot filament. By reflecting back to the hot filament, radia-tion which is not desired to be emitted from the lamp con-serves the energy otherwise required to maintain the filament at operating temperature and thus reduces overall energy re-quirements for operating the lamp.
One of the alternative forms which optical coating 14 may take is the coating design 14A depicted in Fig. 2 and having the design parameters set forth in Table 1 below. The over-all performance of the coating is depicted in Fig. 4. As shown by the dashed curve 22, the coating 14A has high trans-mittance in the visible region of ~he electromagnetic radia-tion spectrum ~etween 400 nanometers and 700 nanometers and has a high reflectance throughout the remainder of the spec-trum, principally the near infrared where there is substan-tial emission of electromagnetic radiation by the hot fila-ment of the lamp, as shown by the curve 21 in Fig. 4.
Fig. 3 illustrates the radiant power spectrum from a 3,000 ~elvin black body and shows that only a small percentage of 77U~
LAYER INDEX OFTHICKNESS (nm) QWOT*
5 Air 1.000 1 1.45894.28 550
2 2.130129.11 1100
3 1.458188.56 1100
4 2.130129.11 1100 10 5 1.458188.56 1100 6 2.130129.11 1100 7 1.458188.56 1100 8 2.130129.11 1100 9 1.458188.56 1100 1510 2.130129.11 1100 11 1.45894.28 550 11' 1.45894.28 550 12 1.458180.00 1050 13 2.130123.24 1050 2014 1.458360.00 2100 2.130123.24 1050 16 1.458360.00 2100 17 2.130123.24 1050 18 1.458360.00 2100 2519 2.130123.24 1050 1.458180.00 550 20' 1.45894.28 550 21 1.~5877.14 450 22 2.130105.63 900 3023 1.458154.28 900 24 2.130105.63 900 1.458154.28 900 26 2.130105.63 900 27 1.45877.14 450 Substrate 1.460 *Quarter Wave Optical Thickness (i.e. reference wavelength at which layer has a quarter wave optical thickness) the total radiation from the filament of a halogen cycle lamp is in the visible light region between 40n and 700 nano-meters. The majority of the emitted radiation is in the in-frared region above the visible light region of the spectrum.
Unless the lamp is to be used for both heating and lighting, the emission of the infrared radiation from the lamp is wasteful of energy and in some applications produces an un-desirable heating of the surrounding environment. For ex-ample, in theater and stage lighting where high intensity il-lumination is required, the heating effect from the high in-tensity lamps is unwelcome since it overheats the area which is being illuminated. By employing a visible light transmit-ting, infrared reflecting optical coating 14 on the lamp 10, the emitted radiation in the infrared region is reflected back to the filament 15 where it serves a useful purpose in keeping the filament heated and yet the major portion of the visible light emitted by the filament escapes the lamp and perform useful work in illuminating the surrounding environ-ment.
Referring specifically to Fig. 2 and Table 1, it is seen that the performance of the overall filter depicted in Fig. 4 is attained in this instance by combining three types of dielec-tric stacks into an overall interference filter 14A. As 25 shown in Table 1, the layers labeled 21-27 form a first di-electric stack I which has a dielectric stack design general-ly expressed as (L/2 H L/2)3 and comprises a shortwave pass interference filter at a design wavelength of 900 nanometers.
The spectral reflectance of this shortwave pass stack is de-picted in Fig. 5. This dielectric stack is considered a shortwave pass stack since it has very low reflectance at wavelengths less than the design wavelength of 900 nanometers and then a region of substantial reflectance at wavelengths greater than 900 nanometers. The second dielectric stack II
35 is a 2:1 dielectric stack at a design wavelength of 1050 nanometers and having a stack design generally expressed as (LHL)4. The spectral reflectance of this 2:1 stack is de-picted as the curve 24 in Fig. 6.
~ ~7 ;~ ~ O 4 The third dielectric stack III utilized in the coating 14A
is a shortwave pass filter at a design wavelength of 1100 nanometers and having a design generally expressed as (L/2 H L/2)5. In each of the above design expressions for the various dielectric stacks I, II, and III, the "L" desig-nates a layer of low refractive index material (i.e. silicon dioxide in this case) which has a quarterwave optical thick-ness at the design wavelength. Similarly, the designation "H" refers to a layer of higher refractive index material (i.e. tantalum pentoxide in this case) which has a quarter-wave optical thickness at the design wavelength. Referring to the shortwave pass stack I for which the design specifica-tion is (L/2 H L/2)3, it is thus seen that each of the L/2 layers in the formula are layers which have an optical thick-ness equal to an eighth wave at the design wavelength. Inthe physical filter embodiment,the first and last layers in the stack I, i.e. layers 21 and 27 in Table 1 are actual eighth wave layers of the low index silicon dioxide material.
On the other hand, layers 23 and 25 turn out to be quarter-wave layers since they consist of two eighth wave layersformed at the same time. This same analysis holds for the shortwave pass stack III which utilizes five components of a (L/2 H L/2) design. The layers 1 and 11 are eighth wave layers, whereas the layers 3, 5, 7, and 9 turn out physically to be quarterwave layers, being the sum of two eighth wave layers. Furthermore, in actually building the filter, the layers 11, 11', and 12 become one physical layer and the layers 20, 20', and 21 become a single physical layer of the low index silicon dioxide material.
The designations for the respective layers on the righthand side of Fig. 2 should be interpreted as follows: the H and L designations again refer to a quarterwave layer of low and high index material respectively and the subscripts A, B, and C refer to the three different design wavelengths where A
signifies design wavelength of 900 nanometers, B designates a i~7~;'704 design wavelength of 1050 nanometers, and C designates a de-sign wavelength of 1100 nanometers.
Other types of optical coatings may also be useful on the halogen cycle lamp 10 depicted in Fig. 1. For example, an optical coating 18 may be formed on the end reflectors 17 of the lamp. In this case, the optical coating 18 may be designed to reflect all components of the radiation emitted by the filament 15 since this will tend to maintain the energy emitted in the directions of the end reflectors with-in the cavity of the envelope 12 where it can do useful work in heating the filament and otherwise maintaining the inter-nal temperature of the lamp.
Other designs for the optical filter 14 may also be desirable in certain applications. For example, in certain applica-tions a colored light output is desired from the lamp. One way of achieving a colored light output is to filter the vis-ible light emitted from the lamp through an absorbing-type color filter which transmits only the desired component of the visible light spectrum. However, such an absorbing fil-ter wastes the energy emitted from the lamp and dissipates it in the filter itself. In accordance with this invention, the optical coating 14 may be designed to have a passband which encompasses only a selected portion of the visible spectrum such that only that portion of the radiation emit-ted by the lamp exits the lamp and all radiation at adjacent wavelengths including portions of the visible and the infra-red are reflected back into the lamp and onto the filament to increase the energy efficiency of the overall lamp. The design of a narrow bandpass filter having high transmittance only in a portion of the visible light spectrum corresponding to the color desired to be emitted from the lamp is well within the skill of the art, for example, by following the general teachings in Chapter 7 of H. A. Macleod's, Thin Film Optical Filters, American Elsevier Publishing Company, New York (1969). Such filters could also be designed uti-770~
lizing the concept set forth in Chapter 20 of MIL HBK. 144 published in October, 1962 by The Department of Defense.
Chapter 20 is entitled "~pplication of Thin Film Coatings"
and is authored by Philip Baumeister. Each of these refer-ence works is incorporated by reference into this applicationas teaching all dielectric optical filter designs and design concepts which could employ the principles of this invention.
In other words, it should be unders~ood that this invention is generally applicable to all types of optical filters and in particular optical interference filters of the bandpass or edge filter type.
Generally the optical coating 14 shown in Fig. 1 would be formed on the lamp envelope 11 in a vacuum deposition chamber utilizing standard vacuum coating technology. For example, deposition of the optical coating on a small diameter lamp envelope may be accomplished in a standard planetary type de-position chamber by adding another degree of rotation which rotates each quartz lamp tube along its axis so that all por-tions of the outer surface thereof are uniformly exposed tothe deposition source within the chamber. Generally, both the silicon dioxide and the tantalum pentoxide layers of the coating will be deposited in a reactive gas mode, onto a sub-strate which is maintained at a temperature of at least about 275C. Either electron beam evaporation sources or resis-tance heated sources may be utilized. Reactive gas deposi-tion involves bleeding oxygen into the chamber during the deposition process. To obtain a good yield of optical coat-ings on lamp envelopes having a small radius of curvature, it has been found preferable to arrange the deposition source with respect to the quartz tube substrate such that the aver-age angle of arrival of the deposited material at the sub-strate will not exceed about thirty-five degrees.
Optical coatings employing the principles and materials of this invention have been built and tested at temperatures up to 1100C. At temperatures below 1100C, the optical perfor-1~7~t~4 mance of the filter remains substantially constant with no evidence of loss of adhesion of the coating, increase in absorption of the coating or interdiffusion of the layers of the coating. It has also been found that by baking the coat-ing at 1100C in air for a number of hours, the coating canbe transformed from a visible light transmit~ing, infrared reflecting filter to a substantially visible light scatter-ing, infrared reflecting filter. The spectral performance of such a filter is depicted in Fig. 8. When the optical coating is exposed to this level of temperature in air for a significant period of time, the coating breaks up into many small islands which are very scattering for light in the visible portion of the spectrum but appear to radiation in the infrared region as a continuous reflecting film. The spectral performance depicted in Fig. 8 is for an optical coating of the design set forth in Table 1 above. Other coating designs could be fashioned which would optimize the scattering in the visible region and otherwise change the spectral transmittance, reflectance and scattering response of the filter.
Actual halogen cycle lamps employing the optical coating de-sign depicted in Fig. 2 and set forth in Table 1 above have been fabricated and tested to demonstrate the improvement in energy efficiency of the lamp with the optical coating ap-plied. 1500 watt lamps have been tested and have shown per-formance improvements in the range of twenty-five to thirty percent. These proven performance improvements correlate well with theoretical percentage improvements values which have been calculated to be in the thirty to thirty-five per-cent region.
As previously indicated, the principles of this invention could be applied in other types of lamp environments such as arc discharge lamps in which an excited plasma emits light of various wavelengths. Due to the large number of free electrons in the plasma, plasma is a good absorber as well as a good emitter. Consequently, the concept of reflecting unwanted components of the light emit~ed from the plasma back into the plasma should also improve the energy efficiency of arc lamps. The principles of this invention may also be applied to laser pump lamps which utilize either a plurality of flash lamps or continuously operated incandescent lamps surrounding a ruby rod within a cavity. Since the ruby laser rod only absorbs light in certain portions of the spectrum, improvements in energy efficiency can be achieved by placing on the pumping lamps an optical coating which only transmits useful light to the laser rod. The unwanted light is reflected back into the pumping lamp to improve the lamp's efficiency.
While the principles of this invention have been discussed above in connection with several alternative embodiments, it should be understood that numerous other applications of the principles may be found by those of ordinary skill in this art. Accordingly, the invention is not limited to the speci-fic exemplary applications described above but may be employ-ed in any high temperature coating environment where optical coating may be employed to improve some aspect of the per-formance of the device to which the coating is applied.
Unless the lamp is to be used for both heating and lighting, the emission of the infrared radiation from the lamp is wasteful of energy and in some applications produces an un-desirable heating of the surrounding environment. For ex-ample, in theater and stage lighting where high intensity il-lumination is required, the heating effect from the high in-tensity lamps is unwelcome since it overheats the area which is being illuminated. By employing a visible light transmit-ting, infrared reflecting optical coating 14 on the lamp 10, the emitted radiation in the infrared region is reflected back to the filament 15 where it serves a useful purpose in keeping the filament heated and yet the major portion of the visible light emitted by the filament escapes the lamp and perform useful work in illuminating the surrounding environ-ment.
Referring specifically to Fig. 2 and Table 1, it is seen that the performance of the overall filter depicted in Fig. 4 is attained in this instance by combining three types of dielec-tric stacks into an overall interference filter 14A. As 25 shown in Table 1, the layers labeled 21-27 form a first di-electric stack I which has a dielectric stack design general-ly expressed as (L/2 H L/2)3 and comprises a shortwave pass interference filter at a design wavelength of 900 nanometers.
The spectral reflectance of this shortwave pass stack is de-picted in Fig. 5. This dielectric stack is considered a shortwave pass stack since it has very low reflectance at wavelengths less than the design wavelength of 900 nanometers and then a region of substantial reflectance at wavelengths greater than 900 nanometers. The second dielectric stack II
35 is a 2:1 dielectric stack at a design wavelength of 1050 nanometers and having a stack design generally expressed as (LHL)4. The spectral reflectance of this 2:1 stack is de-picted as the curve 24 in Fig. 6.
~ ~7 ;~ ~ O 4 The third dielectric stack III utilized in the coating 14A
is a shortwave pass filter at a design wavelength of 1100 nanometers and having a design generally expressed as (L/2 H L/2)5. In each of the above design expressions for the various dielectric stacks I, II, and III, the "L" desig-nates a layer of low refractive index material (i.e. silicon dioxide in this case) which has a quarterwave optical thick-ness at the design wavelength. Similarly, the designation "H" refers to a layer of higher refractive index material (i.e. tantalum pentoxide in this case) which has a quarter-wave optical thickness at the design wavelength. Referring to the shortwave pass stack I for which the design specifica-tion is (L/2 H L/2)3, it is thus seen that each of the L/2 layers in the formula are layers which have an optical thick-ness equal to an eighth wave at the design wavelength. Inthe physical filter embodiment,the first and last layers in the stack I, i.e. layers 21 and 27 in Table 1 are actual eighth wave layers of the low index silicon dioxide material.
On the other hand, layers 23 and 25 turn out to be quarter-wave layers since they consist of two eighth wave layersformed at the same time. This same analysis holds for the shortwave pass stack III which utilizes five components of a (L/2 H L/2) design. The layers 1 and 11 are eighth wave layers, whereas the layers 3, 5, 7, and 9 turn out physically to be quarterwave layers, being the sum of two eighth wave layers. Furthermore, in actually building the filter, the layers 11, 11', and 12 become one physical layer and the layers 20, 20', and 21 become a single physical layer of the low index silicon dioxide material.
The designations for the respective layers on the righthand side of Fig. 2 should be interpreted as follows: the H and L designations again refer to a quarterwave layer of low and high index material respectively and the subscripts A, B, and C refer to the three different design wavelengths where A
signifies design wavelength of 900 nanometers, B designates a i~7~;'704 design wavelength of 1050 nanometers, and C designates a de-sign wavelength of 1100 nanometers.
Other types of optical coatings may also be useful on the halogen cycle lamp 10 depicted in Fig. 1. For example, an optical coating 18 may be formed on the end reflectors 17 of the lamp. In this case, the optical coating 18 may be designed to reflect all components of the radiation emitted by the filament 15 since this will tend to maintain the energy emitted in the directions of the end reflectors with-in the cavity of the envelope 12 where it can do useful work in heating the filament and otherwise maintaining the inter-nal temperature of the lamp.
Other designs for the optical filter 14 may also be desirable in certain applications. For example, in certain applica-tions a colored light output is desired from the lamp. One way of achieving a colored light output is to filter the vis-ible light emitted from the lamp through an absorbing-type color filter which transmits only the desired component of the visible light spectrum. However, such an absorbing fil-ter wastes the energy emitted from the lamp and dissipates it in the filter itself. In accordance with this invention, the optical coating 14 may be designed to have a passband which encompasses only a selected portion of the visible spectrum such that only that portion of the radiation emit-ted by the lamp exits the lamp and all radiation at adjacent wavelengths including portions of the visible and the infra-red are reflected back into the lamp and onto the filament to increase the energy efficiency of the overall lamp. The design of a narrow bandpass filter having high transmittance only in a portion of the visible light spectrum corresponding to the color desired to be emitted from the lamp is well within the skill of the art, for example, by following the general teachings in Chapter 7 of H. A. Macleod's, Thin Film Optical Filters, American Elsevier Publishing Company, New York (1969). Such filters could also be designed uti-770~
lizing the concept set forth in Chapter 20 of MIL HBK. 144 published in October, 1962 by The Department of Defense.
Chapter 20 is entitled "~pplication of Thin Film Coatings"
and is authored by Philip Baumeister. Each of these refer-ence works is incorporated by reference into this applicationas teaching all dielectric optical filter designs and design concepts which could employ the principles of this invention.
In other words, it should be unders~ood that this invention is generally applicable to all types of optical filters and in particular optical interference filters of the bandpass or edge filter type.
Generally the optical coating 14 shown in Fig. 1 would be formed on the lamp envelope 11 in a vacuum deposition chamber utilizing standard vacuum coating technology. For example, deposition of the optical coating on a small diameter lamp envelope may be accomplished in a standard planetary type de-position chamber by adding another degree of rotation which rotates each quartz lamp tube along its axis so that all por-tions of the outer surface thereof are uniformly exposed tothe deposition source within the chamber. Generally, both the silicon dioxide and the tantalum pentoxide layers of the coating will be deposited in a reactive gas mode, onto a sub-strate which is maintained at a temperature of at least about 275C. Either electron beam evaporation sources or resis-tance heated sources may be utilized. Reactive gas deposi-tion involves bleeding oxygen into the chamber during the deposition process. To obtain a good yield of optical coat-ings on lamp envelopes having a small radius of curvature, it has been found preferable to arrange the deposition source with respect to the quartz tube substrate such that the aver-age angle of arrival of the deposited material at the sub-strate will not exceed about thirty-five degrees.
Optical coatings employing the principles and materials of this invention have been built and tested at temperatures up to 1100C. At temperatures below 1100C, the optical perfor-1~7~t~4 mance of the filter remains substantially constant with no evidence of loss of adhesion of the coating, increase in absorption of the coating or interdiffusion of the layers of the coating. It has also been found that by baking the coat-ing at 1100C in air for a number of hours, the coating canbe transformed from a visible light transmit~ing, infrared reflecting filter to a substantially visible light scatter-ing, infrared reflecting filter. The spectral performance of such a filter is depicted in Fig. 8. When the optical coating is exposed to this level of temperature in air for a significant period of time, the coating breaks up into many small islands which are very scattering for light in the visible portion of the spectrum but appear to radiation in the infrared region as a continuous reflecting film. The spectral performance depicted in Fig. 8 is for an optical coating of the design set forth in Table 1 above. Other coating designs could be fashioned which would optimize the scattering in the visible region and otherwise change the spectral transmittance, reflectance and scattering response of the filter.
Actual halogen cycle lamps employing the optical coating de-sign depicted in Fig. 2 and set forth in Table 1 above have been fabricated and tested to demonstrate the improvement in energy efficiency of the lamp with the optical coating ap-plied. 1500 watt lamps have been tested and have shown per-formance improvements in the range of twenty-five to thirty percent. These proven performance improvements correlate well with theoretical percentage improvements values which have been calculated to be in the thirty to thirty-five per-cent region.
As previously indicated, the principles of this invention could be applied in other types of lamp environments such as arc discharge lamps in which an excited plasma emits light of various wavelengths. Due to the large number of free electrons in the plasma, plasma is a good absorber as well as a good emitter. Consequently, the concept of reflecting unwanted components of the light emit~ed from the plasma back into the plasma should also improve the energy efficiency of arc lamps. The principles of this invention may also be applied to laser pump lamps which utilize either a plurality of flash lamps or continuously operated incandescent lamps surrounding a ruby rod within a cavity. Since the ruby laser rod only absorbs light in certain portions of the spectrum, improvements in energy efficiency can be achieved by placing on the pumping lamps an optical coating which only transmits useful light to the laser rod. The unwanted light is reflected back into the pumping lamp to improve the lamp's efficiency.
While the principles of this invention have been discussed above in connection with several alternative embodiments, it should be understood that numerous other applications of the principles may be found by those of ordinary skill in this art. Accordingly, the invention is not limited to the speci-fic exemplary applications described above but may be employ-ed in any high temperature coating environment where optical coating may be employed to improve some aspect of the per-formance of the device to which the coating is applied.
Claims (13)
1. A coated article useful in high temperature environments substantially in excess of 500°C comprising a substantially transparent substrate formed of a material adapted to with-stand said high temperature environment and an optical coat-ing formed on one surface of said substrate and comprising a first set of layers consisting at least primarily of silicon dioxide and a second set of layers consisting at least pri-marily of tantalum pentoxide.
2. A coated article as claimed in Claim 1, wherein said op-tical coating comprises an interference filter formed of alternating layers of said first and second sets.
3. A coated article as claimed in Claim 2, wherein said in-terference filter is a bandpass filter designed to transmit radiation in a preselected first wavelength band and to reflect radiation in adjacent wavelength regions.
4. A coated article as claimed in Claim 3, wherein said bandpass filter is a hot mirror having high transmittance for visible light and high infrared reflectance.
5. A coated article as claimed in Claim 3, wherein said bandpass filter is a cold mirror having high reflectance for visible light and high infrared transmittance.
6. A coated article as claimed in Claim 3, wherein said bandpass filter is a color filter having high transmittance for a preselected portion of the visible light spectrum and high reflectance for adjacent spectral regions.
7. A coated article as claimed in any of Claims 4 or 6, wherein said substrate comprises fused silica formed into a lamp envelope adapted to be utilized in a halogen cycle in-candescent lamp operating at an outer envelope surface tem-perature of at least about 800°C and said interference filter is formed on said outer surface of said lamp envelope.
8. A coated article useful in high temperature environments substantially in excess of 500°C comprising a substantially transparent substrate formed of a material adapted to with-stand said high temperature environment, and an optical coat-ing formed on one surface of said substrate and comprising a multilayer interference filter having high reflectance of in-frared radiation and high scattering of visible light, said interference filter being formed by depositing on said sub-strate a multilayer dielectric stack composed of alternate layers consisting at least primarily of silicon dioxide and tantalum pentoxide and then baking said coated substrate in air at a temperature of at least about 1100°C.
9. A halogen lamp comprising a lamp envelope having a geome-try which has an internal focal point, line or plane and formed of a substantially transparent material capable of withstanding operating temperatures of at least about 800°C;
a high melting point metal filament mounted within said lamp envelope substantially at said focal point, line or plane; a halogen gas filling said envelope; and an interference filter formed on an outer surface of said lamp envelope and compris-ed of alternate layers consisting at least primarily of silicon dioxide and tantalum pentoxide.
a high melting point metal filament mounted within said lamp envelope substantially at said focal point, line or plane; a halogen gas filling said envelope; and an interference filter formed on an outer surface of said lamp envelope and compris-ed of alternate layers consisting at least primarily of silicon dioxide and tantalum pentoxide.
10. The halogen lamp of Claim 9, wherein said interference filter is a bandpass filter having high transmittance of visible light and high reflectance of infrared radiation.
11. The halogen lamp of Claim 9, wherein said interference filter is a bandpass filter having high transmittance for radiation in a preselected portion of the visible light spec-trum and high reflectance of radiation in adjacent wavelength regimes so that the light output of said lamp is a preselect-ed color.
12. The halogen lamp of Claim 9, wherein said interfer-ence filter is an infrared reflecting, visible light scattering filter formed by depositing on said outer surface of said lamp envelope a multilayer dielectric stack primarily of said silicon dioxide and tantalum pentoxide layers having a high transmittance of visible light and high infrared reflectance and then baking said envelope and filter in air at a temperature of at least about 1100°C to convert said filter from a visible light transmitting filter to a substantially visible light scattering filter.
13. A halogen lamp as claimed in any of Claims 9, 11, or 12, wherein said lamp envelope comprises a generally cy-lindrical envelope and reflectors are mounted in each end of said envelope, said reflectors being formed of a sub-stantially transparent material having a multilayer in-terference filter formed thereon comprised of alternate layers consisting at least primarily of silicon dioxide and tantalum pentoxide and having high reflectance for all radiation emitted by said filament.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US28455381A | 1981-07-20 | 1981-07-20 | |
US284,553 | 1981-07-20 |
Publications (1)
Publication Number | Publication Date |
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CA1177704A true CA1177704A (en) | 1984-11-13 |
Family
ID=23090633
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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CA000407537A Expired CA1177704A (en) | 1981-07-20 | 1982-07-19 | Optical coatings for high temperature applications |
Country Status (5)
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JP (1) | JPS5865403A (en) |
CA (1) | CA1177704A (en) |
DE (1) | DE3227096A1 (en) |
FR (1) | FR2509874B1 (en) |
GB (1) | GB2103830B (en) |
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JPS5958753A (en) * | 1982-09-28 | 1984-04-04 | 株式会社東芝 | Incandescent bulb |
DD226742A3 (en) * | 1983-04-04 | 1985-08-28 | Zeiss Jena Veb Carl | INTERFERENCE FILTER WITH A THROUGH BAND |
US4588923A (en) * | 1983-04-29 | 1986-05-13 | General Electric Company | High efficiency tubular heat lamps |
US4535269A (en) * | 1983-08-01 | 1985-08-13 | General Electric Company | Incandescent lamp |
JPH0612663B2 (en) * | 1984-06-05 | 1994-02-16 | 東芝ライテック株式会社 | Incandescent light bulb |
JPS61101949A (en) * | 1984-10-24 | 1986-05-20 | 東芝ライテック株式会社 | Bulb |
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NL191813C (en) * | 1985-06-11 | 1996-08-02 | Philips Electronics Nv | Electric lamp equipped with an interference filter. |
US4689519A (en) * | 1985-10-23 | 1987-08-25 | U.S. Philips Corporation | Electric lamp having an outwardly extending protrusion |
DE3538996A1 (en) * | 1985-11-02 | 1987-05-14 | Philips Patentverwaltung | Interference filter |
HU198254B (en) * | 1987-03-11 | 1989-08-28 | Tungsram Reszvenytarsasag | Projector lamp |
DE3814539A1 (en) * | 1988-04-29 | 1989-11-09 | Heraeus Gmbh W C | LIGHTING ARRANGEMENT WITH HALOGEN BULB |
US4949005A (en) * | 1988-11-14 | 1990-08-14 | General Electric Company | Tantala-silica interference filters and lamps using same |
JP2626061B2 (en) * | 1989-06-17 | 1997-07-02 | 東芝ライテック株式会社 | Incandescent light bulb |
CA2017471C (en) * | 1989-07-19 | 2000-10-24 | Matthew Eric Krisl | Optical interference coatings and lamps using same |
JPH03233501A (en) * | 1990-02-09 | 1991-10-17 | Copal Co Ltd | Optical multilayered film filter element and production thereof |
US5179468A (en) * | 1991-11-05 | 1993-01-12 | Gte Products Corporation | Interleaving of similar thin-film stacks for producing optical interference coatings |
US5422534A (en) * | 1992-11-18 | 1995-06-06 | General Electric Company | Tantala-silica interference filters and lamps using same |
EP0657752A1 (en) * | 1993-12-08 | 1995-06-14 | Osram Sylvania Inc. | Optical coating and lamp employing same |
JP3261961B2 (en) * | 1995-12-20 | 2002-03-04 | ウシオ電機株式会社 | Discharge lamp |
AU2003270193A1 (en) | 2002-09-14 | 2004-04-08 | Schott Ag | Layer system comprising a titanium-aluminium-oxide layer |
JP4643202B2 (en) * | 2004-08-20 | 2011-03-02 | 日本電波工業株式会社 | Optical low-pass filter |
DE102004054872B4 (en) * | 2004-11-12 | 2009-12-03 | Auer Lighting Gmbh | reflector lamp |
Family Cites Families (12)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
BE792316A (en) * | 1971-12-07 | 1973-06-05 | Philips Nv | PROCESS FOR MAKING MIRRORS FOR COLD LIGHT |
US3848152A (en) * | 1972-06-06 | 1974-11-12 | Corning Glass Works | Electric lamp having a fused silica glass envelope |
CA1013804A (en) * | 1973-10-23 | 1977-07-12 | Gte Sylvania Incorporated | Incandescent lamp with infrared reflective coating |
NL7405071A (en) * | 1974-04-16 | 1975-10-20 | Philips Nv | LIGHT BULB WITH INFRARED FILTER. |
JPS551339Y2 (en) * | 1974-07-16 | 1980-01-16 | ||
US4006378A (en) * | 1975-10-01 | 1977-02-01 | General Electric Company | Optical coating with selectable transmittance characteristics and method of making the same |
DE2637616A1 (en) * | 1976-08-20 | 1978-02-23 | Siemens Ag | FILTER FOR PHOTODETECTORS |
DE2658623C2 (en) * | 1976-12-23 | 1982-07-29 | Dr. Johannes Heidenhain Gmbh, 8225 Traunreut | Recording media and process for its manufacture |
US4160929A (en) * | 1977-03-25 | 1979-07-10 | Duro-Test Corporation | Incandescent light source with transparent heat mirror |
DE2834161C2 (en) * | 1977-08-11 | 1985-01-17 | Optical Coating Laboratory Inc., Santa Rosa, Calif. | Silicon solar cell array |
US4229066A (en) * | 1978-09-20 | 1980-10-21 | Optical Coating Laboratory, Inc. | Visible transmitting and infrared reflecting filter |
FR2474701A1 (en) * | 1979-12-19 | 1981-07-31 | France Etat | INTERFERENTIAL OPTICAL FILTER FOR PROTECTION AGAINST INFRARED RADIATION AND APPLICATION |
-
1982
- 1982-07-19 CA CA000407537A patent/CA1177704A/en not_active Expired
- 1982-07-20 FR FR8212669A patent/FR2509874B1/en not_active Expired
- 1982-07-20 DE DE19823227096 patent/DE3227096A1/en not_active Withdrawn
- 1982-07-20 GB GB08220976A patent/GB2103830B/en not_active Expired
- 1982-07-20 JP JP57126607A patent/JPS5865403A/en active Pending
Also Published As
Publication number | Publication date |
---|---|
GB2103830A (en) | 1983-02-23 |
DE3227096A1 (en) | 1983-02-03 |
FR2509874B1 (en) | 1986-05-09 |
FR2509874A1 (en) | 1983-01-21 |
JPS5865403A (en) | 1983-04-19 |
GB2103830B (en) | 1985-04-17 |
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