JPH09246632A - Gas laser resonator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas laser oscillator which provides a high-power and high-optical quality laser with a small beam spread angle and is capable of being easily Q-switched. SOLUTION: This oscillator is divided into an optical resonator and optical amplifier 4; the resonator is disposed across a gas passage to flow a laser medium and outputs a high-optical quality laser having a comparatively low power, the amplifier 4 has total reflection mirrors 41-44 opposed across the passage 1 to form an amplifier 4 in the space passing this passage 1, a beam expander 3 expands the beam of an output laser light 21 received from the resonator and transmits it to the amplifier 4 which amplifies the beam to radiate a high-power beam.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas laser oscillator, and more particularly to a structure of a laser resonator and an amplifier that efficiently oscillates a large-capacity gas laser with good light quality.

[0002]

2. Description of the Related Art A laser device requires a laser medium for amplifying light by stimulated emission and an optical resonator for returning the light to satisfy the resonance condition of the laser. The optical resonator is composed of a reflector that reflects light. The optical resonator is formed in the middle with a laser medium sandwiched therebetween, and is designed to collect the light energy emitted when the laser medium falls to the ground state and extract it as laser light.

In a high-power laser oscillator, mirrors having large apertures are used facing each other in order to obtain energy from a larger amount of medium, and the energy trapped in the resonator is also large. Therefore, the laser beam diameter is large, and if a stable resonator is applied to, for example, an iodine laser, it has a high-order Gaussian mode of about 20 to 30, so that the laser light emitted from the laser device has a high divergence and a high quality. It becomes a bad beam. Further, the high energy in the resonator causes thermal distortion of the mirror holder, which tends to make the optical axis unstable.

In order to lower the Gaussian mode, even if an aperture having a small diameter hole is inserted into the resonator,
The beam diameter becomes thin and a large output cannot be obtained, which is not realistic. Further, the heat generated in the resonator is also large, which causes the resonator reflector to be distorted due to heating, thereby deteriorating the quality of light. Moreover, when a Q-switch element such as an electro-optic crystal or a mechanical chopper is inserted into the waveguide to output a pulsed laser beam, the energy in the waveguide is large, so the durability of the inserted switch element is high. And energy loss becomes a problem.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a laser resonator which outputs a large capacity laser with good light quality. Another object is to provide a laser resonator that is a high-power laser and can be easily Q-switched.

[0006]

In order to solve the above-mentioned problems, a gas laser resonator according to the present invention has a flow path through which a laser medium that amplifies light is circulated, and a resonator reflecting mirror including the flow path. An optical resonator that forms a laser medium, a beam expander that expands the luminous flux of the output laser light of the optical resonator, and a total reflection mirror that are arranged to face each other with the flow path sandwiched in the space that passes through the flow path. An amplifier for forming a laser medium, amplifying the light expanded by the beam expander with the laser medium, and emitting the amplified light.

It is preferable that the optical resonator is provided with an aperture holder and the aperture is arranged by the holder so that the center of the hole is aligned with the central axis of the resonator mirror. Further, it is preferable that the aperture holder has a structure in which the aperture can be attached / detached and has a structure capable of forced cooling. Further, an optical switching element may be provided in the optical resonator.

The gas laser resonator may be one in which the laser medium is iodine and an iodine laser is generated. Further, in the case of the iodine laser resonator, it is preferable that the total reflection mirror is covered with the total reflection film for iodine laser and the reflection film for helium / neon laser. It is preferable that the gas laser resonator of the present invention further includes a visible light laser device that can be used for alignment, and irradiates the visible light laser from the back of the resonance reflecting mirror facing the output reflecting mirror of the optical resonator. The visible light laser device is preferably a helium / neon laser device.

In the gas laser resonator of the present invention, instead of the mechanism of generating a large output at once in the optical resonator, the resonator portion and the amplifying portion are separated so that the both share the same laser medium, and the beam extract between them is performed. It has a structure that connects with a panda.
Therefore, when the laser medium is introduced into the flow path, the light emitted by the laser medium is confined in the resonator in the resonator and amplified. A part of the light is extracted as seed light, widened by a beam expander, and projected on the amplification unit. The amplification unit guides the widened seed light into the laser medium, the seed light is supplied with energy from the laser medium while being transmitted through the laser medium, is amplified, and is emitted from the window as high-power laser light.

Since the laser energy in the resonator is extremely small compared to the final output, it is easy to handle, and for example, a Fabry-Perot resonator can be manufactured with high precision.
Further, since the heat generation is small, the degree of deformation during use is small, and the influence on the dimension that affects the quality of light such as the curvature of the reflecting mirror surface is small. Therefore, the seed light output from the resonator has a small spread, a low Gaussian mode, and high light quality.

On the other hand, since the full width of the gas flow path in the amplifying section is used to reciprocate as much as necessary, the space in which the laser light contacts the laser medium can be increased, so that the laser light is resonated in the resonator section. The laser medium that has not been consumed in is effectively utilized and amplified, and then emitted from the laser device. Of course, the effect does not change when the amplifying section is placed upstream of the flow of the laser medium in the channel and the resonator section is placed downstream. In this way, the gas laser resonator of the present invention is
By providing a low-power resonator and an amplifier that amplifies it as a widened beam in the same channel, the laser medium inserted in the channel is effectively used to generate a high-power, high-power laser. can do.

A gas laser resonator having an aperture holder in the optical resonator resonates only the light near the optical axis passing through the hole by inserting the aperture in the optical resonator. Laser light having the following Gaussian mode can be generated. It is difficult to insert an aperture into the conventional high-power laser resonator because it receives strong energy and is damaged.

Further, if the aperture holder can be attached and detached, the aperture having the optimum hole diameter can be selected and replaced even if the conditions change, which is convenient in design or operation. In addition, if the structure can be forcibly cooled, the light energy that is projected to the periphery of the aperture hole and converted into heat can be quickly removed, so that damage to the device can be avoided and the life can be maintained. For cooling, various methods such as a method of forming a circulation path in an aperture holder to pass cooling water, electronic cooling using the Peltier effect, and heat removal by a heat pipe can be used.

The mirror and aperture in the optical resonator section determine the Gaussian mode of the laser light. However, since the resonator section has low energy, there is little deformation of the resonator reflecting mirror, and the optimum aperture is selected to select the optical axis. Since it can be inserted inside, the light quality is high and stable despite the high final laser output. Further, since the energy standing in the optical resonator is relatively small, it is possible to insert an optical switch element in the resonator, which allows the laser light to be pulsed. An electro-optic crystal, an acousto-optic switch, or a mechanical chopper can be used as the optical switch.

If a visible light laser device that can be used for alignment is provided and the visible light laser is irradiated from the back of the resonance reflecting mirror facing the output reflecting mirror of the optical resonator, the output laser is visible. The optical path of the laser beam can be traced correctly even when it is not visible because it is not light, or when the wavelength range is an obstacle to human beings and the output is large and it damages the eyes and thus should not be viewed directly. , Alignment becomes easier.

The conventional high-power iodine laser is one in which a single laser resonator generates a high-power laser beam, or a laser beam from a low-power oscillator is amplified by a multistage amplifier. Since the laser beam diameter is large, in the case of a stable resonator, the Gaussian mode has a high order of 20 to 30 and the light quality is low, and the latter has a problem that the device is complicated and expensive, whereas the Gaussian mode has a problem. Since low-order and high-power output can be obtained efficiently, these problems can be solved.

Further, when an attempt is made to perform alignment using a helium / neon laser, the conventional mirror has a smaller mirror reflectance for an iodine laser (wavelength: 1.315 μm) than a helium / neon laser (wavelength: 633 nm). Therefore, if it is reflected many times in the optical path, there is a problem that it is attenuated on the way and becomes invisible. Therefore, each total reflection mirror is provided with a coating that reflects well at the wavelength of 633 nm of a helium-neon laser to facilitate optical axis alignment. In the case of an iodine laser resonator, it is necessary to cover each total reflection mirror with a total reflection film for iodine laser so as not to absorb a ray of 1.315 μm, but further cover with a reflection film for helium / neon laser. Thus, the optical axis can be adjusted by reflecting the light of the wavelength of 633 nm by using an inexpensive and simple helium-neon laser device.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION A gas laser resonator according to the present invention will be described in detail below with reference to the drawings. FIG. 1 is a conceptual diagram illustrating one embodiment of a gas laser resonator of the present invention.
The present embodiment is intended for a laser resonator in an iodine laser device. In the figure, 1 is a cavity through which excited iodine atoms serving as a laser medium flow. The flow 1a of excited iodine atoms flows from top to bottom in the figure. The excited iodine atom emits light having a wavelength of 1.315 μm when it is stimulated by laser light and returns to the ground state.

The optical resonator 2 is a Fabry-Perot type resonator comprising a resonator reflecting mirror 22 and an output side resonator reflecting mirror 24. The reflecting mirror 24 on the output side is a plane mirror coated so as to transmit a part of the incident iodine laser light, and the resonator reflecting mirror 22 facing it is surface-coated so as to reflect 100% of the iodine laser light. It is a concave mirror. The two reflecting mirrors face each other across the gas flow path 1 and form a seed light output in-resonator laser beam 2a. The light emitted from the excited iodine atom is confined in the resonator and amplified while reciprocating in the flow 1a of the excited iodine atom, and a part thereof is emitted from the output reflecting mirror 24 as the laser light 2b.

Since the laser output 2b is relatively small, for example, about 100 W and the beam diameter is small, the structure of the resonator portion including the reflecting mirror is easy to manufacture and can be manufactured at low cost. Further, since the energy trapped in the resonator is small, the heat generated inside is small and the deformation due to the heat is small. Therefore, the laser light has a low-order Gaussian mode close to a single mode with a small spread, and the light quality is good.

Reference numeral 3 is a beam expander comprising a convex mirror 32 and a concave mirror 34. The laser output 2b emitted from the optical resonator 2 is first projected on the convex mirror 32 and expanded to become a parallel beam 4a having a diameter of about 20 mm at the concave mirror 34.

Reference numeral 4 is an amplifier. The amplification unit 4 is composed of total reflection mirrors 41, 42, 43, 44, ... The total reflection mirror is a plane mirror provided with a coating that totally reflects the iodine laser. The respective pairs of total reflection mirrors are arranged in parallel with each other with the gas flow path 1 interposed therebetween, and the laser beam that has entered is formed by reciprocating between the total reflection mirrors while slightly shifting the optical path. The parallel beam 4a incident from the beam expander 3 crosses the gas flow path 1 every time it travels between the reflecting mirrors, and the gas flow path 1
Energy is supplied from the excited iodine atom 1a flowing inside to be amplified.

Since the diameter of the laser beam in the amplification section 4 is large and the laser beam crosses the flow 1a of excited iodine atoms many times, the contact area between the laser beam and the excited iodine atoms is large and the amplification factor is also high. 20 kW in this embodiment
The laser beam 4b of a certain degree is emitted. Amplifier 4
Since the amplification in (1) does not deteriorate the light quality of the laser beam so much, the emitted laser light 4b becomes a high-quality laser light in which the high quality of the output laser 4a in the optical resonator 2 is maintained.

Reference numeral 5 is a window for taking out the laser light while keeping the gas laser resonator secret. After that, the laser light is focused, injected into an optical fiber having a core diameter of 0.3 mm, and conveyed to a use position.

In the above embodiment, the Fabry of the optical resonator 2
In the Perot type resonator, a concave mirror that totally reflects is arranged as the resonator reflecting mirror 22, and a plane mirror that partially transmits is arranged as the reflecting mirror 24 on the output side. However, both of them are plane mirrors, concave mirrors, It may be configured by only one type of convex mirror, or one may be configured by a convex mirror and the other by a concave mirror. Further, the method for extracting the laser output from the optical resonator 2 is not the so-called coupling mirror method as described above, but a coupling hole method or a resonator in which a small hole is provided in the center of the output reflecting mirror to extract the laser output. Various methods such as a method of providing a semitransparent reflecting mirror and taking it out can be applied.

The beam expander 3 uses a combination of a convex mirror and a concave mirror, but it goes without saying that a method using an optical lens or the like may be used. Further, only two pairs of total reflection mirrors of the amplifying section 4 are drawn for convenience of drawing representation, but there is no change in technical idea even if there are any pairs. It should be noted that the total reflection mirrors are depicted as being independent for each pair, but if they are each composed of a single plane reflection mirror with the gas flow path 1 in between, the number of parts is small and the parallelism can be adjusted easily. There is an effect. 1 illustrates the case where the resonance reflecting mirrors 22 and 24, the total reflecting mirrors 41, 42, ... Are arranged outside the gas flow path 1, but all or a part of them are arranged in the gas flow. It may be stored in the road 1.

FIG. 2 is a conceptual diagram of a resonator portion showing a case where an aperture and a pulse generating element are inserted inside the optical resonator 2 of the present invention. In the following, in the drawings, constituent elements having the same functions as those in the above figures are designated by the same reference numerals to simplify the description. Resonator reflector 2 of optical resonator 2
The aperture device 6 and the pulse generating element 7 are arranged outside the flow 1a of excited iodine atoms in the intracavity laser beam 2a formed between the laser reflector 2 and the resonator reflector 24 on the output side. In the conventional high-power laser resonator, it was difficult to insert an element into the resonator portion, but in the laser resonator of the present invention, the amplifier portion is separated, so the resonator portion is small, the load is small, and the energy trapped is small. Since a small amount of heat is generated, it becomes possible to dispose an aperture device, a pulse generating element, etc. in the optical resonator. Therefore, various measures for improving the light quality of laser light have become possible.

An aperture plate 62 having a small hole 63 can be attached to the aperture holder body 61 of the aperture device 6. Strictly adjust so that the center of the small hole 63 is on the central axis of the resonator 2. Since the spatial spread of the laser light becomes larger as the mode becomes higher, the small holes 6
The Gaussian mode of the laser light can be set to a low order by selecting the diameter of 3 so as to give a diffraction loss sufficient to suppress oscillation with respect to the higher order modes of the laser light standing in the resonator 2. it can. Since the optimum value of the hole diameter of the aperture plate 62 changes depending on the conditions, the aperture plate 62 has a structure such that it can be easily attached and detached by, for example, screwing in order to have flexibility in design.

The aperture device 6 absorbs the energy of light cut by the aperture and its temperature rises, causing thermal distortion in the entire device to destabilize the optical axis, and promotes reaction with iodine in the atmosphere. Corrosion of the aperture plate 62 may be accelerated. Therefore, the aperture device 6
It is preferable to circulate cooling water inside to remove heat.

FIG. 3 is an enlarged cross-sectional view showing a state in which the aperture device 6 is cut along the plane perpendicular to the optical axis of the resonator 2 at the cooling water supply pipe, and FIG. 4 is I in FIG.
It is sectional drawing when it cut | disconnects by a V-IV surface. A through hole 64 is provided on the central axis of the aperture holder body 61, and an aperture plate 62 having a hole 63 having an appropriate diameter is concentrically fixed thereto. Around the through hole 64, a hole 65 through which cooling water flows is provided. A supply pipe 66 and a discharge pipe 67 communicate with this hole 65, and the cooling water supplied from the supply pipe 66 flows around the through hole 64 and is discharged from the discharge pipe 67 to flow into the aperture device. Dissipate the heat. The cooling of the aperture device 6 is not limited to cooling water, and various methods such as an electronic cooling method and a method of carrying heat to an external low temperature heat source by a heat pipe to cool it can be used.

Further, an optical switch element 7 can be provided in the optical resonator 2. As the optical switch, a conventionally known electro-optical crystal, acousto-optical switch, mechanical chopper, or the like can be used to pulse-oscillate the laser light.

FIG. 5 is a view showing a gas laser resonator in which the helium / neon laser device 8 is placed far behind the resonant reflecting mirror 22 of the optical resonator 2 to facilitate the alignment. A helium / neon laser device 8 for alignment is placed far behind the resonance reflecting mirror 22 of the optical resonator 2, and the helium / neon laser 8 is placed behind the resonance reflecting mirror 22.
Irradiate a 633 nm visible light laser of a. Resonance reflector 2
2 and 24 have a reflectance of nearly 100% with respect to the wavelength of the iodine laser, but are transparent to the helium-neon laser, the helium-neon laser 8a follows the optical path of the optical resonator 2 as it is and is a beam. The convex mirror 32, the concave mirror 34 of the expander 3, and the total reflection mirror 4 of the amplifier 4
1, 42, ... Passes along the locus of the central axis of the optical path of the iodine laser and is emitted from the window 5. Since this helium-neon laser is visible light, it is possible to perform alignment while observing it.

However, the reflecting mirrors are coated with a coating having a high reflectance with respect to the wavelength of the iodine laser, but since this coating is almost transparent to the helium-neon laser, the helium-neon laser 8a is entirely transparent. In some cases, the reflections 41, 42, ... Are attenuated and become invisible while being repeatedly reflected. Therefore, in the present embodiment, the total reflection mirror surface is provided with a coating that reflects both the iodine laser and the helium / neon laser.

[0034]

As described above, the gas laser resonator of the present invention has a system configuration in which the optical resonator section and the optical amplifier section are separated and the same laser medium is used. The quality of the laser light can be improved, and the amplification unit can perform amplification while maintaining the light quality. Even though it is a high-power laser generator, it is possible to obtain high-quality laser light with a small spread. . Further, since a large output laser is obtained by effectively utilizing the laser medium in a gas laser such as an iodine laser, it is possible to provide a more economical device.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing one embodiment of a gas laser resonator of the present invention.

FIG. 2 is a conceptual diagram showing an optical resonator portion in another embodiment of the present invention.

3 is a cross-sectional view showing an example of an aperture holder used in the optical resonator of FIG.

4 is a cross-sectional view taken along the line IV-IV in FIG.

FIG. 5 is a conceptual diagram showing still another embodiment of the present invention.

[Explanation of symbols]

 1 Gas Flow Path 1a Flow of Excited Iodine Atom 2 Optical Resonator 22, 24 Resonator Reflector 2a Intracavity Laser Beam 2b Laser Output Light 3 Beam Expander 32 Convex Mirror 34 Concave Mirror 4a Parallel Beam 4 Amplifier 41, 42, 43 , 44 ... Total reflection mirror 4b Laser beam 5 Window 6 Aperture device 61 Aperture holder body 62 Aperture plate 63 Small hole 64 Through hole 65 Cooling water flow hole 66 Supply pipe 67 Discharge pipe 7 Optical switch element 8 Helium neon laser Device 8a Helium-neon laser

Claims (6)

[Claims] 1. A laser medium for generating and amplifying light, an optical resonator including one partial transmission mirror and at least one total reflection mirror, and a beam diameter of a laser beam output from the optical resonator. A beam expander and a plurality of total reflection mirrors are arranged to face each other across the laser medium to form an amplification section that passes through the laser medium a plurality of times, and the light from the beam expander is transmitted by the amplification section. A gas laser resonator comprising: an amplifier configured to amplify and emit. 2. The gas laser resonator according to claim 1, further comprising an aperture holder for holding an aperture having a hole in the optical resonator. 3. The gas laser resonator according to claim 2, wherein the aperture holder can attach and detach the aperture,
A gas laser resonator having a structure capable of forced cooling. 4. The gas laser resonator according to any one of claims 1 to 3, wherein an optical switch element is provided in the optical resonator. 5. The gas laser resonator according to claim 1, wherein the total reflection mirror is covered with a laser total reflection film serving as a main body and an optical axis adjusting laser reflection film. Characteristic gas laser oscillator. 6. The gas laser resonator according to claim 1, further comprising a visible light laser device that can be used for optical axis adjustment, and an output reflecting mirror of the optical resonator. A gas laser resonator characterized by irradiating a visible light laser from the back of an opposing oscillator reflector.