[go: up one dir, main page]
More Web Proxy on the site http://driver.im/

CA1177704A - Optical coatings for high temperature applications - Google Patents

Optical coatings for high temperature applications

Info

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
Application number
CA000407537A
Other languages
French (fr)
Inventor
James D. Rancourt
Robert L. Martin, Jr.
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Optical Coating Laboratory Inc
Original Assignee
Optical Coating Laboratory Inc
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Optical Coating Laboratory Inc filed Critical Optical Coating Laboratory Inc
Application granted granted Critical
Publication of CA1177704A publication Critical patent/CA1177704A/en
Expired legal-status Critical Current

Links

Classifications

    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01KELECTRIC INCANDESCENT LAMPS
    • H01K1/00Details
    • H01K1/28Envelopes; Vessels
    • H01K1/32Envelopes; Vessels provided with coatings on the walls; Vessels or coatings thereon characterised by the material thereof
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00Optical elements other than lenses
    • G02B5/20Filters
    • G02B5/28Interference filters
    • G02B5/281Interference filters designed for the infrared light
    • G02B5/282Interference 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.

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
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.

Claims (13)

WHAT IS CLAIMED IS:
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.
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.
CA000407537A 1981-07-20 1982-07-19 Optical coatings for high temperature applications Expired CA1177704A (en)

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
CA1177704A true CA1177704A (en) 1984-11-13

Family

ID=23090633

Family Applications (1)

Application Number Title Priority Date Filing Date
CA000407537A Expired CA1177704A (en) 1981-07-20 1982-07-19 Optical coatings for high temperature applications

Country Status (5)

Country Link
JP (1) JPS5865403A (en)
CA (1) CA1177704A (en)
DE (1) DE3227096A1 (en)
FR (1) FR2509874B1 (en)
GB (1) GB2103830B (en)

Families Citing this family (23)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
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
NL8500368A (en) * 1985-02-11 1986-09-01 Philips Nv YELLOW HALOGEN CAR LAMP.
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)

* Cited by examiner, † Cited by third party
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

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

Similar Documents

Publication Publication Date Title
US4663557A (en) Optical coatings for high temperature applications
CA1177704A (en) Optical coatings for high temperature applications
US5723937A (en) Light-scattering coating, its preparation and use
US5627426A (en) Lamp with IR reflecting film and light-scattering coating
US4160929A (en) Incandescent light source with transparent heat mirror
US4366407A (en) Incandescent lamp with selective color filter
JPH0612663B2 (en) Incandescent light bulb
US4645290A (en) Selective color filter
US20060007677A1 (en) Optimal silicon dioxide protection layer thickness for silver lamp reflector
US5550423A (en) Optical coating and lamp employing same
EP0617300B1 (en) Lamp with IR reflecting film and light-scattering coating
US6049169A (en) Electric lamp having optical interference filter of alternating layers of SiO2 and Nb2 O5 --Ta2 O5
US8253309B2 (en) Incandescent lamp incorporating reflective filament supports and method for making it
US5705882A (en) Optical coating and lamp employing same
EP0197931A1 (en) Variable index film for transparent heat mirrors
US6471376B1 (en) Increased life reflector lamps
US5142197A (en) Light interference film and lamp
US6710520B1 (en) Stress relief mechanism for optical interference coatings
JP2687243B2 (en) Multilayer optical interference film
EP0588541A1 (en) Electric incandescent lamps
JP2971773B2 (en) Multilayer film
JP2928784B2 (en) Multilayer reflector
WO2008078241A1 (en) White light emitting electric lamp assembly
JP3054663B2 (en) Multilayer reflector
Aleksandrov et al. Multilayer film structures for light sources

Legal Events

Date Code Title Description
MKEC Expiry (correction)
MKEX Expiry