JPS61129601A - Laser optical member - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical member for a laser. More particularly, it relates to optical elements (such as windows, for example) that are exposed to a large photon flux in the cooling gas region of a gas slave and undergo photoreduction as a result.

[Prior art and problems]

In most gas ion lasers, there is a reduction in useful laser power output over the operating life of the laser. This power reduction is facilitated by losses in the optical elements of the laser tube, such as window(s).

For lasers operating with large gains (eg, lasers oscillating at visible light frequencies), undesirable losses from optical elements such as windows are often tolerated during the operational life of the Teague. However, even in such high gain lasers, it is desirable to eliminate or minimize losses. Eliminating or minimizing losses in the optical elements (windows) can extend the useful life of the tube and increase the efficiency and precision of tube operation during its life.

In the case of a laser that oscillates at a certain ultraviolet frequency.

The reduction in useful power, accelerated by losses in windows, for example, can be very significant.

Grass generated inside the gas ion laser tube! Maarks can produce large photon fluxes. The photon flux can initiate physical and chemical changes on the surface of the optical element exposed to it. In more detail.

These photon fluxes can result in photoreduction of the exposed surface of the optical element.

Examples of materials used for optical elements in such lasers include the following: However, it is not limited. That is, crystal S fol r S ′ + dissolved SiO3,
BeO, Y2O3, sapphire, diamond, B
@O, MgF', , ZnS.

Zn5e, BaF2, CaF, carmonoid diamond.

Yztrium aluminum garnet (YAG)
.

Yztrium Fist Lithium Fluoride (YT, F).

Others. These materials often undergo physical and chemical changes, especially photoreduction, on surfaces exposed to a photon flux. In the case of a window mounted at the end of the laser chip, this change occurs on the inner surface of the window. Other optical elements placed inside the tube itself are also subject to photoreduction.

It would be of great benefit in the art to provide laser optics that do not undergo photoreduction when exposed to large photon fluxes. In particular, this is a significant benefit in the case of lasers that emit ultraviolet radiation.

Such lasers produce ultraviolet radiation as part of or parasitic to the beam. An example of such a laser is the noble gas ion laser, Exai? -(exc
imer) laser, CO, laser, free electron laser,
Atomic metal vapor lasers, and others.

[Summary of the invention]

One object of the present invention is to provide a laser optical member that does not undergo photoreduction even when exposed to a large photon flux generated within the laser.

Another objective is to minimize photoreductive changes during laser operation on the inner surface of the window attached to the laser chip end.

Another objective is to minimize other physical or chemical changes induced on the surface of the laser optic by the photon flux.

Another objective is to minimize the photon flux induced light emission of optical elements attached to the cooling gas region of the gas ion laser.

Another objective is to substantially increase the useful life of the laser cheap by minimizing physical and chemical changes such as photoreduction on the optical confection caused by the photon flux.

Another object is to increase the radiation resistance of an optical element attached to a cooling gas region of a gas ion laser. The present invention provides an optical component for a laser of the type having a hot gas glazma region and a cooling gas region. be. A photon flux is produced during operation of the laser. An optical element is included having at least one surface exposed to and in communication with the photon flux. A coating means is deposited on the surface of the optical element that is exposed to the photon flux.

The coating means is formed of a material that minimizes photoreduction of the optical element induced by the photon flux.

In another feature of the invention, an optical element operatively associated with the laser passes the photon flux through the cooling gas region.

The optical member includes an optical element having at least one surface exposed to a photon flux. A coating is deposited on the exposed surface, the coating being selected from a stoichiometric standpoint such that it does not substantially change upon exposure to the generated photon flux.

In another feature of the invention, a window structure is attached to the end of a laser tube of a type that generates a large photon flux during operation. The photon flux can initiate physical and chemical changes on the surfaces it exposes. The window structure includes a window means made of a transparent optical member that is transparent to the laser light beam.

Furthermore, a radiation-resistant and optically transparent coating means is included on the inner surface of the window means which is exposed to the large photon flux. The coating means prevents or minimizes physical and chemical changes that occur on the surface during laser operation.

The invention is applicable to optical elements attached to the cooling gas region of a laser that generates ultraviolet radiation during operation. Exemplary lasers include rare gas ion lasers, excimer lasers, CO, lasers, free electron lasers, atomic vapor lasers, and others. The present invention provides a bulk coating on the surface of an optical element that is exposed to a large photon flux;
It thereby results in a laser with long lifetime, high economy and good efficiency. The coating is selected to specifically minimize photoreduction effects caused by photon flux exposure.

The invention is not limited to windows, but includes intracavity lenses,
It also includes other laser optics such as mirrors, birefringent plates, polarizing elements, etc.

Coatings serve many useful functions. First, photoreduction of the surface exposed to the photon flux is minimized. Next, the radiation hardness of the optical element is increased. Furthermore, 1M
, minimizing optical degradation that can result from optical radiation absorption or in-phase wavefront distortion of the optical surface.

In certain embodiments of the invention, the optical element is a window.

More specifically, it is a Brewster angle window. The window.

It is part of a laser that oscillates in the ultraviolet frequency range and produces relatively low gain. In this particular example, the window material is crystalline 5t02 and the coating is At,03
and other oxides. Further, in this embodiment, the coating is a thin layer approximately 100 Angstroms thick.

The aforementioned optical components and coating methods are further objects of the invention.

Other objects of the invention are apparent from the following description and drawings. The examples described below are merely illustrative and do not limit the invention. Many modifications and improvements may be made without departing from the true scope of the invention.

[Description of preferred embodiment]

In FIG. 1, the entire laser chip is designated by reference numeral 10.
Indicated by

The laser tube 10 shown in FIG. 1 has 7! / Laser tube for a ion laser, only one end of which is shown.

Laser tube 10 basically consists of two parts. namely, a cooling gas section 12 and a hot gas glazma section 14. The types of lasers utilized with the present invention are those that generate ultraviolet radiation either as part of the laser beam itself or as parasitic radiation.

The hot gas is found within the plasma site 14 where the laser action as a result of population inversion produces a laser beam of a selected wavelength. This high temperature gas.

It is not found within the cooling gas section 12.

Although an ion laser is shown in FIG.
It should be understood that other lasers producing strong photon fluxes are also applicable. The invention is applicable to the following types of lasers: Noble gas ion; excited? (!X
eimeF): COf: Free electron; Atomic metal vapor; Others. Furthermore, the present invention.

The chain 7'IO, which can also be used with lasers having various geometries such as ring lasers and folded lasers, includes two cylindrical members 16 and a cathode assembly 18. The high temperature glazma is connected to the cathode assemblies 18 and 7.
The interior of the cylindrical member 16 (remains) between the nodes (not shown).

In the illustrated construction, the attachment of end flanges 20.22 for attaching the tube end assembly (cooling gas section 12) to the cylindrical member 16 provides an arrangement.

The 7-run 22 includes one or more connector assemblies 24, 26 for connecting vacuum pumps, filler units, and other auxiliary equipment.

As shown in FIG. 1, an optical element in the form of a window 28 is attached to the end of the cooling gas section 12 of the tube io. 1st
Although windows are shown in the drawings, the present invention includes an intracavity lens,
Miller, Grieflint
t) 7′ rate, polarizing plate.

It is possible to implement with other optical elements such as other polarizers and the like. It should be noted that the optical elements of the present invention are not limited and are merely listed.

In the particular embodiment of FIG. 1, window 28! Attach to one star angle. However, the present invention is not limited to mounting windows or other optical elements at Brewster's angle. It is also possible to mount the window at other angles as well as other optical elements.

Laser tube 10 has another electrode, an anode (not shown), at the end of the tube. ! Lasma arcs can produce large photon fluxes during laser operation. These large photon fluxes.

It can be helpful to reduce the useful power output of the laser tube. The reason is that there are losses in optical elements such as, but not limited to, single or multiple windows in the tube. A large photon flux accumulates depending on photon energy, photon flux density and exposure time. From the standpoint of antecedent factors as well as specific applications, approximately 10
'. The range of ~1020 photons/second is considered large.

A laser beam generated by the laser tube 10.

It is designated by reference numeral 30 in FIG.

In one embodiment, window 28 is attached to tube 10 in a lath frit manner. This method is.

A glass frit 29 is interposed between the chain 7'IO and the window 28. What are the actual installation steps?

It is a conventional frit procedure that seals at high temperatures of about 45Q°C to 550°C. Use of epoxy and cement.

Other attachment procedures such as optical contact, melting, use of deformable gaskets, etc. are also appropriate. However, standard frit procedures are preferred.

Window 28'fr: Any loss of transmitted beam 30 passing through.

resulting in a loss of useful power output of the laser.

At the optical element consisting of window 28, an optical drop (op
tical degradation) may result in lasing. Damage to the optical element may result in absorption of optical radiation or distortion of the phase front di
tortion).

Optical degradation to an optical element can occur as a result of physical or chemical changes on a surface of the optical element (eg, surface 32 of window 28). The reason is.

This is because this is the surface that is exposed to a large photon flux generated by the glazma arc during operation of the laser (0). photor
education). Throughout this specification.

Physically and chemically induced changes are simply described in terms of photoreductive changes.

The present invention minimizes photoreductive changes on exposed optical surfaces by increasing the optical surface's radiation resistance. This is achieved according to the invention by applying a radiation-resistant and optically transparent coating 34 to the optical element surfaces exposed to the photon flux, in particular the surfaces within the cooling gas section 12.

Throughout this specification, the term radiation resistive refers to the fact that the coating 34 does not undergo any physical or chemical changes when exposed to ultraviolet radiation generated during laser operation. Furthermore, the radiation resistance in that sense is two-intensity and time/
Controlled by 4 lameter. That is, the greater the intensity of the photon flux and the longer the exposure time of the photon flux, the greater the radiation resistance of the coating must be. In this regard, the term used in the present invention (radiation resistance) is:
The limitation is that the radiation resistance of coating 34 is limited under conditions during laser operation. Laser operation (
Under conditions of extreme strength and long durations not normally required, the coating 34 is not radiation resistant and may become damaged.

Coating 34 serves many useful functions.

It is a material that does not substantially change the optical properties of the optical element. For example, coating 34 is transparent to the wavelength of interest. The coating 34 is designed to minimize reflection losses when the coating is applied (e.g., when the window is mounted at Brewster's angle).
Select the reflection coefficient of

A coating 34 is deposited on optical element surfaces that are exposed to large photon fluxes to minimize possible photoreduction on those surfaces. Furthermore, the coating 34.

A stoichiometry that does not substantially change when exposed to a photon flux. It minimizes adhesive failure on exposed surfaces. Furthermore, coating 34 itself does not substantially absorb laser at the desired wavelength during or after exposure to ultraviolet radiation. Stoichiometry, as defined herein, is a concept that includes conservation of material and chemical activation energy.

Suitable optical element materials include: However, it is not limited to these. Namely.

Crystalline SiO2. St, dissolved Sin, sapphire, diamond, Bed, MgF2, ZnS
, Zn5e, BaF2. CaF3, BeO
, Y2O3, carmonoid diamond, yttrium,
These include aluminum garnet (YAG), yttrium lithium fluoride (YLF), and others.

A preferred material is crystalline SiO2. Suitable coating materials are those that substantially reduce photoreduction of the optical element surface. When deposited on the optical surface to be protected, these materials have low reflectivity, low optical absorption in the lasing region, and low scattering at the wavelengths in the lasing region. Illustrative (non-limiting) examples of coating materials include:

As below □ A403, BsO, Y, 0
3. MgO.

B2O3,5c203, LiF, NdF3
, ThF4, MgF', , Na5AtF'
6゜Others. The most preferred materials are At, O8 and BeO.

Coating 34 may be comprised of multiple layers, such as a single layer or multiple layers. Coating 34 includes a first coating of a first selected material.
layers, a second layer of a second selected material, and so on. When multiple layers are used, they are arranged to minimize reflection losses due to the combination of coated surface 32 and coating 34.

The materials for coating 34 and coated surface 32 are advantageously selected to reduce absorption of surface 32 by contaminants. Surface 32 would, but for coating 34, undergo light attenuation due to exposure to the photon flux.

The thickness of coating 34 can vary. Coating 34 can also be a thin film having a thickness of about 50 angstroms or more. Further, it is possible to apply the coating to an optical thickness of half a wavelength (absent layer), or it can be applied to an optical thickness of an integral multiple of a half wavelength.

Coating 34 can be applied to the optical element by nine different means. In one embodiment, the coating is applied to the desired surface(s) by physical vapor deposition using a variety of application means, such as an electron beam gun, spray gun, or the like. The above application means are not limited.

In other embodiments, the coating is applied by chemical deposition or stoichiometric dipping (if covering the entire optical element).

If you refer to Figure 3, Laser Chase! Optical element 28 is shown positioned within 10 . More specifically, optical element 28 is located within cooling gas region 12 . Reference numerals used herein refer to similar or identical elements in the figures. As shown in FIG. 3, both sides 38 of an optical element 28, such as a polarizing plate, birefringent plate, intracavity lens, etc., are coated with a coating 34. Optical element 28 may or may not be mounted at Brewster's angle. Two surfaces of the optical element are coated when each surface is in communication with a large photon flux and minimizing photoreduction on each surface is desired.

In other embodiments, only one side of optical element 28 is coated. Furthermore, when two sides are coated, each surface with the same material or with a different material.

Alternatively, they can be coated in any manner, such as with different thicknesses or with multiple layers on one or both.

Referring to FIG. 3, at one end of the chain 10 is a laser output mirror 36. Mirror 36 is attached to tube 10 by a variety of conventional means, including frit sealing. It is not limited to these means. The internally exposed surface 38 of the tube 10 is coated with a coating 34. It should be understood that optical elements such as mirror 36 may be comprised of multiple layers.

The present invention can be applied with lasers that emit ultraviolet light, visible light, infrared light, and others.

In one embodiment of the invention, a window is installed at the end of the cooling gas region of a laser chip that oscillates in the ultraviolet frequency range. In this example, the window is made of crystalline Si
Made of O2, the coating material is applied by physical vapor deposition to approximately 10%
Farts coated to a physical thickness of 0 angstroms, O5
It is.

Ultraviolet frequency lasers operate at low gain and suffer losses in optical elements such as windows.

This can result in a reduction in the useful power of the laser over short time intervals.

For example, a large photon flux can result in photoreduction of the surface of crystalline SiO2. This is the reduction of SiO2 to atomic Si and other reducing substances. If atomic Si is present on the surface, it exhibits optical losses such as absorption, scattering, etc. in the excavation wave length. Even a small atomic layer of atomic Si can absorb significant amounts of laser beam light.

A403, Boo et al. coatings coated with thin films or half-wavelength optical thicknesses (or multiples thereof).

It is effective in minimizing photoreduction of SiO2.

The coating material used is also a radiation-hard material in the sense that it does not easily dissociate and does not change stoichiometry under conditions of exposure to large photon fluxes.

Although specific embodiments of the invention have been described, many modifications and variations are possible.

It is to be understood that these variations are within the scope of the invention as claimed.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway side view of a laser tube of the type to which the present invention can be applied. 2 is an enlarged longitudinal sectional view of the window structure used in the laser tube of FIG. 1. FIG. FIG. 3 is an enlarged longitudinal sectional view showing a cooling gas portion of an ion laser to which the present invention can be applied. [Explanation of main symbols] 10...Laser tube 12...Cooling gas section 14...High temperature gas glamor section 16...Cylindrical member 18...Cathode assembly 20.22...End Franz 24.26 ...Connector assembly 28...Window 29...Glass 7 lit 30...Transmitted beam 32...Surface 34...-Coating 36...Laser output mirror 38...Surface Patent Applicant Nichtler Inox Incorporated

Claims (1)

[Scope of Claims] 1. An optical component of a laser having a hot gas plasma region, a cooling gas region and an internally generated photon flux, consisting of the following means: exposed to and communicating with said photon flux; an optical element having at least one surface in relationship and operatively associated with the laser; and formed of a material that minimizes photoreduction of the optical element induced by the photon flux; Coating means on the surface of the optical element that is exposed to the photon flux. 2. The optical member according to claim 1, wherein the optical element is made of a substantially transparent optical material that transmits a laser light beam. 3. The optical member according to claim 1, wherein the optical element has one or more surfaces exposed to the photon flux. 4. Each surface of the optical element exposed to the photon flux,
The optical member according to claim 3, wherein the optical member is coated with the coating means. 5. The optical member according to claim 1, wherein the coating means is an optically thin film. 6. The optical member of claim 1, wherein said coating means has a physical thickness of about 50 angstroms or more. 7. The optical member of claim 1, wherein said coating means has a physical thickness of about 100 Angstroms. 8. The coating means is applied to each optical element exposed surface with an optical thickness of substantially half a wavelength or an integral multiple of a half wavelength; optical components. 9. Optical element according to claim 1, wherein said coating means is multilayered, each layer being made of a different material. 10. The optical element according to claim 1, wherein the optical element is a window at the end of the laser tube forming the cooling gas region. 11. The optical member according to claim 10, wherein the window is a frit sealed to the laser tube. 12. The optical member according to claim 10, wherein the window is a Brewster angle window. 13. The optical element is located inside the cooling zone and has two opposing surfaces; at least one of the surfaces is exposed to the photon flux; and a coating means is applied on the exposed surface. The optical member according to claim 1. 14. The optical member according to claim 1, wherein the optical element is an intracavity lens. 15. The optical member according to claim 1, wherein the optical element is a birefringent plate. 16. The optical member according to claim 1, wherein the optical element is an internal plate polarizer. 17. The optical member according to claim 1, wherein the optical element is a mirror. 18. The optical element of claim 1, wherein the optical element is made of a material that minimizes chemical bond breaking in the optical element induced by the photon flux. 19. The optical element is made of crystalline SiO_2, Si, dissolved S
iO_2, sapphire, diamond, BeO, MgF
_2, ZnS, ZnSe, BaF_2, CaF_2, carbon-like diamond, yttrium aluminum
Optical element according to claim 1, made of a material selected from the group consisting of garnet (YAG), yttrium lithium fluoride (YLF) and others. 20. The optical member according to claim 1, wherein the coating means is an oxide. 21. Optical element according to claim 1, wherein the coating means is made of a material having low reflectance, low optical absorption and low scattering in the operating spectrum of the laser. 22. The optical element of claim 1, wherein said coating means is adapted to minimize changes or alterations in optical in-phase wavefronts that occur after exposure to said photon flux. 23. The optical element of claim 1, wherein the optical element and coating means are selected to reduce the absorption of contaminants on the surface of the optical element coated with the coating means. 24, the coating means includes Al_2O_3, Be
O, Y_2O_3, MgO, B_2O_3, Sc_2O
_3, LiF, NdF_3, ThF_4, MgF_2 and Na_3AlF_6. Optical element according to claim 1. 25, the coating means is Al_2O_3 or B
The optical member according to claim 1, wherein the optical member is made of eO. 26. The optical member according to claim 1, wherein the coating means is made of Al_2O_3. 27. The optical element is a Brewster angle window attached to the end of the laser tube in the cooling gas region, the inner surface of which communicates with the cooling gas region; the coating means is a thin layer of Al_2O_3; The window is crystalline SiO
_2; and wherein the laser is a gas ion laser. 28. An optical element operatively associated with a laser for generating a photon flux in a cooling gas region, comprising the following means: having at least one surface exposed to said photon flux;
an optical element attached to said laser; and a coating made of a material having a stoichiometry that does not substantially change upon exposure to said photon flux and deposited on said exposed surface. 29. The optical member according to claim 28, wherein the optical element is made of a material that transmits a laser light beam. 30. The optical element of claim 28, wherein the laser is of a type that generates ultraviolet radiation during laser operation. 31. The optical member according to claim 28, wherein the laser is an ion laser. 32. The optical member of claim 28, wherein the coating has a physical thickness of about 50 Angstroms or more. 33. The optical member of claim 28, wherein the coating has a physical thickness of about 100 Angstroms. 34. The optical element of claim 28, wherein the coating consists of a plurality of different layers formed of different materials. 35. The optical member of claim 28, wherein the coating has an optical thickness of a half wavelength or an integral multiple of a half wavelength. 36. The optical element of claim 28, wherein the optical element is a window attached to the end of the laser tube, the surface of the window being exposed to the photon flux within the cooling gas region. Element. 37. The optical member according to claim 36, wherein the window is a Brewster angle window. 38. The optical element of claim 28, wherein the optical element is located within the cooling gas region. 39. The optical member according to claim 28, wherein the optical element is a polarizing plate. 40. The optical member according to claim 28, wherein the optical element is an intracavity lens. 41. The optical member according to claim 28, wherein the optical element is a birefringent plate. 42. The optical member according to claim 28, wherein the optical element is a mirror. 43. The optical element of claim 28, wherein the optical element has one or more surfaces coated with the coating. 44. The optical element of claim 28, wherein the coating is deposited on the optical element by physical vapor deposition. 45. The optical element of claim 28, wherein the coating is deposited on the optical element by chemical vapor deposition. 46, The optical element is made of crystalline SiO_2, Si, dissolved S
iO_2, sapphire, diamond, BeO, MgF
_2, ZnS, ZnSe, BaF_2, CaF_2, carbon-like diamond, yttrium aluminum
29. An optical member according to claim 28, made of a material selected from the group consisting of garnet (YAG), yttrium lithium fluoride (YLF). 47. The optical member according to claim 28, wherein the coating is an oxide or a fluoride. 48, the coating means includes Al_2O_3, Be
O, Y_2O_3, MgO, B_2O_3, Sc_2O
29. Optical element according to claim 28, made of a material selected from the group consisting of: -3, LiF, NdF_3, ThF_4, MgF_2 and Na_3, AlF_6. 49, the coating means is Al_2O_3 or B
The optical member according to claim 28, wherein the optical member is made of eO. 50. The optical element of claim 28, wherein the optical element and coating means are selected to reduce the absorption of contaminants on the surface of the optical element coated with the coating means. 51. A window structure mounted at the end of a laser tube of a type that generates a large photon flux during operation that can initiate physical or chemical changes on the exposed window surface, comprising: a window means made of a transparent optical member for transmitting a passing laser light beam; and a window means on the inner surface of the window means exposed to a large photon flux and exposed during laser operation. A radiation-resistant and optically transparent coating means to minimize or prevent physical and chemical changes to the surface. 52. The window structure of claim 51, wherein said coating means is a very thin layer to minimize absorption and reflection losses between said coating means and said window means. . 53. The window structure of claim 51, wherein the window is a Brewster angle window. 54, wherein said coating means has a reflection coefficient selected to minimize reflection losses between said coating means and said window means;
Window structure described in section. 55. The window structure of claim 54, wherein the window is a Brewster angle window. 56. The window structure of claim 51, wherein said window means and said coating means are selected to reduce absorption of contaminants on said inner surface of said window. 57. The window structure of claim 56, wherein the window is a Brewster angle window. 58. The window structure according to claim 51, wherein the window means is crystalline SiO_2. 59. said coating means consist of a material which absorbs a large part of the photon flux causing physical and chemical changes on said window surface and which does not dissociate under the action of said photon flux; 52. A window structure according to claim 51, wherein a majority of the bundle is prevented from reaching the window surface. 60. A window structure according to claim 59, wherein the window means is crystalline SiO_2. 61. The window structure of claim 51, wherein said coating means comprises a material that resists optical degradation. 62. The window structure of claim 51, wherein the window means is crystalline SiO_2 and the coating means is Al_2O_3. 63. The window structure of claim 62, wherein the window is a Brewster angle window. 64. Deterioration of any window over a period of time causes a reduction in the laser output power and/or an undesired distortion of the in-phase wavefront; the window structure consists of a Brewster angle window; the window means is made of crystalline SiO_2 material; 52. The window structure of claim 51, wherein: and wherein said coating means is coated in a thin layer having a physical thickness in the range of about 100 angstroms. 65, on the inner surface of a window mounted at the end of a laser tube of such a type that during operation generates a large photon flux and which can initiate physical and chemical changes on the exposed window surface. , a method for minimizing or preventing physical or chemical changes, the method comprising the steps of: constructing a window of transparent optical material for transmitting a beam of laser light; and laser operation. for coating the inner surface of said window with a radiation-resistant and optically transparent coating made of a material effective to minimize or prevent physical or chemical alteration of said window surface within said window; step. 66. The method of claim 65, wherein the window is a Brewster angle window.