JPH047111B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a waveguide type gas laser device.

[Technical background and problems of the invention]

Waveguide gas laser devices are small, high-output laser devices that have been rapidly developed in recent years, and are particularly expected to be applied as CO ₂ (carbon dioxide) lasers.

Application fields of CO ₂ lasers include communication using atmospheric propagation, measurement, and radar. Applications in these fields often require broadband CW (continuous wave) operation or rapidly repeating pulse operation. However, with a normal CO ₂ laser, the amplification band is only about 50MHz due to the Doppler width. In order to make a CO ₂ laser broadband, it is possible to utilize the collision spread (approximately 5MHz/Torr) by increasing the gas pressure, but it is extremely difficult to obtain a high-pressure discharge with a normal CO ₂ laser. It is.

A waveguide gas laser device has been proposed as a solution to these problems.

Waveguide-type gas laser devices have a small discharge tube diameter of about 1 mm, making it possible to perform high-pressure continuous discharge, and recently CO ₂ lasers with a high bandwidth of about 1 GHz have been obtained. Furthermore, this waveguide type gas laser device has a smaller tube diameter, so it can obtain higher gain than the normal type, and is expected to be used as a small-sized, high-output laser device.

The basic laser excitation method used in most conventional waveguide gas lasers is to generate a DC discharge along the length of the device between a pair of electrodes located near the ends of the laser waveguide. It is going by.

In such devices, a relatively large DC excitation voltage of approximately 10 kV and the necessary voltage source for this purpose are required.
An electric circuit is required to generate the above voltage.

Also, the various effects that occur in the cathode fall region in the aforementioned longitudinal electrical discharges give rise to several problems.

Firstly, cathode sputtering damages the cathode and shortens the life of the device, and secondly, the high electric field in the cathode drop region dissociates the laser gas.

Additionally, the relatively high cathode drop voltage consumes a significant portion of the input power, reducing operating efficiency. Hardware such as a high-voltage power supply, current regulator, and stabilizing resistor is also required because the sustaining voltage is high and the impedance of the discharge tube is negative.

On the other hand, in conventional pulsed lateral discharge excitation, the excitation pulse period must be short enough to prevent arcing, and it also has the disadvantage of requiring a large and expensive pulse generation network. It was hot.

To overcome these difficulties, a lateral excitation waveguide type gas laser device has already been devised in which a voltage is applied in a direction perpendicular to the direction of laser oscillation to cause discharge.

In this case, the distance between the cathode and the anode is sufficiently short, so that high voltage as in the longitudinal discharge described above is not required.

On the other hand, as for the discharge format, in addition to the conventional DC discharge and pulse discharge, RF (radio frequency) discharge excitation type has also been devised.

This method generally uses a frequency of about 30 MHz to 3 GHz, and since cations with low mobility are mostly moved by the electric field, the above-mentioned sputtering does not occur. Further, since no positive space charge is generated, there is no power consumption due to cathode drop, and highly efficient laser discharge can be obtained.

By the way, generally the laser output is approximately proportional to the length of the laser medium.

Therefore, in order to further increase the output without increasing the overall length of the laser device,
A refraction type method is being considered in which multiple waveguides are folded back with a reflecting mirror and connected in series.

As one such method, a Z-shaped discharge as shown in FIG. 1 has already been considered.

That is, an output mirror 1, a total reflection mirror 2, and a folding mirror 3 are arranged so that the optical path is refracted in a Z shape, and a waveguide 4 is provided in the reflected optical path portion formed by these mirrors. When excitation light is applied to the wave path 4, this light is reflected between each mirror and resonates, the laser is excited, and finally the laser beam 5 is transmitted to the outside through the output mirror 1 formed by a half mirror.
The system is such that it is output.

However, this method has poor space utilization and therefore poor cooling efficiency, so it cannot take advantage of the advantages of waveguide lasers, such as small size and high efficiency.

Furthermore, it is difficult to adjust the reflection direction of the folding mirror 3.

[Purpose of the invention]

The present invention was made in view of the above circumstances, and
The object of the present invention is to provide a gas laser device of the RF discharge lateral excitation waveguide type, which has a small and robust structure, has a high output, is highly stable, and is not difficult to adjust.

[Summary of the invention]

That is, in order to achieve the above object, the present invention provides electrode plates that are spaced apart from each other on at least one pair of opposing side wall surfaces of a block-shaped electrode base that has a cooling means, and that the electrode plates and the side wall surfaces are Dielectric plates facing each other are provided at appropriate intervals between them to form a plurality of waveguides that are open at both ends surrounded by the side wall surface of the electrode base, the electrode plate, and the dielectric plate. In this case, a reflecting mirror is provided with one of the reflecting optical axes aligned with the axis of the waveguide, and a reflecting mirror is provided, and the optical axis of the other reflecting optical axis of the reflecting mirror is aligned with the reflecting mirror of the waveguide to be connected. Each waveguide is connected in series, and a total reflection mirror is provided at one end of the waveguides connected in series, and a semi-transmission mirror is provided at the other end. The configuration is such that the paired mirrors are held on the same holder so that the position of each reflecting mirror is difficult to shift, and by cooling with a cooling means, it is less susceptible to the effects of heat generation due to discharge. Aiming for high output and high stability.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in Figures 2 to 8.
This will be explained with reference to the figures.

FIG. 2 shows the arrangement structure of mirrors constituting a laser resonator in one embodiment of the present invention, and is an exploded perspective view illustrating a folding method that is the central concept of the present invention.

In this device, each mirror is arranged in such a manner that the optical paths L ₁ , L ₂ , L ₃ , and L ₄ in the waveguide, which are arranged parallel to each other at the position of each ridge line on the longitudinal side of the virtual rectangular parallelepiped, are coupled in series. It is provided at both ends of each of the ridge lines so as to

That is, in the figure, 21 is an output mirror such as a half mirror, which reflects part of the light and allows part of the light to pass through. 22 is a total reflection mirror, and these output mirror 21 and total reflection mirror 22 are arranged at both ends of the entire optical path formed by the connected waveguides. 23a, 23b, and 23c are folding mirrors that refract the optical path. Of these, 23a connects the optical paths _L1 and _L2 , and 23b connects the optical paths _L2 and _L3. , 23c are provided to connect the optical paths _L3 and _L4 . These folding mirrors 23a, 23b, and 23c are a pair of reflecting mirrors that are fixed to an integrated holding base so as to form exactly right angles to each other, and the positions of the reflecting mirrors are set as the optical axis positions of the two optical paths to be connected. be.

With this configuration, when excitation light is applied to the optical path within the waveguide, the light is reflected by each mirror and passes through the output mirror 21 and the total reflection mirror 2.
2, and the output is emitted from the mirror 21 to the outside as a laser beam LB.

In addition, with this configuration, the optical path follows each ridgeline position of the rectangular parallelepiped, so if the overall size is the same, the optical path can be longer than the Z-shaped optical path shown in Figure 1. The utilization rate of the space occupied for the formation is also increased.

FIG. 3 shows the configuration of the waveguide body in this device. In the figure, reference numeral 31 denotes an electrode base made of a metal block such as aluminum, and this electrode base 31 is provided with a cooling water passage hole 31a that extends in the longitudinal direction and communicates with the outside.
32a, 32b, 32c, 32d are electrode bases 3
The electrode plates 32a to 32d are arranged parallel to each other with a predetermined gap on the outer surface of the electrode plate 1 in the longitudinal direction.
is formed of a metal plate made of the same material as the electrode base 31. Two electrode plates are disposed on opposite sides of the electrode base 31, spaced apart from each other, and block-shaped dielectric plates 33a, 33b, 33c, 33 made of ceramic or the like are disposed between the electrode base 31 and the electrode base 31.
The four rectangular spaces formed by sandwiching the electrode base 31, the electrode plates 32a to 32d, and the dielectric plates 33a to 33f are waveguides 34a, 34b, 34.
c, 34d are formed. In this case, this waveguide 3
The waveguides 4a to 34d have a cross section of about 1 square millimeter, and the waveguides 34a to 34d are filled with a gas such as _CO2 , argon, neon, etc. as a laser medium. Further, the inner walls of the waveguides 34a to 34d are sufficiently polished, and may be coated with a thin film such as a dielectric material in order to increase the laser gain in some cases.

Note that each electrode plate 32a to 32d has a
An electrode connector 35 is provided for applying an RF field.

In such a configuration, the RF electric field for exciting discharge is generated between the electrode base 31 and the electrode plates 32a to 3.
2d. As a result, RF discharge occurs within the four waveguides 34a to 34d, and the light generated at that time is reflected by each of the mirrors 21 to 23d provided at the ends of the waveguides, resonates within the waveguides, and generates a laser beam. is excited and output. The waveguide main body constituent members are heated by the heat generated by the discharge, and thermal expansion causes misalignment between the optical axes of the mirrors 21 to 23d and the central axes of the waveguides 34a to 34d, or changes in the resonator length. This causes fluctuations in laser output.

In order to reduce this fluctuation, in this device, a cooling water passage hole 31a is provided in the electrode base 31, and cooling water (another coolant may be used) is passed through the hole for cooling. Therefore, heat due to discharge is efficiently removed, so thermal expansion is suppressed, and thereby the laser output fluctuation is suppressed.
Highly stable laser output can be obtained.

FIG. 5 shows a cross-sectional view of the waveguide body having the structure shown in FIG. 3 fixed to the gas-filling outer casing 41.

A laser gas of about 100 Torr is sealed inside the outer casing 41. Particularly in the case of sealed-off type gas laser equipment, the lifespan is affected by gas deterioration and clean-up. Furthermore, if the volume of the gas-filled container is small, the internal temperature will rise due to heat generation due to discharge, and the gas density distribution inside the laser tube will change, resulting in a decrease in output.

In order to reduce such effects, the gas-filling outer casing 41 has a large buffer space as shown in FIG.

The overall structure of the present device is such that mirror mounts 42 and 43 for refracting the optical path are attached to both ends of a laser waveguide main body as shown in FIG. 3 fixed to the outer casing 41, as shown in FIG.

The output mirror 21, the total reflection mirror 22, and the folding mirrors 23a, 23b, and 23c described in FIG. 2 are mounted in the mirror mounts 42 and 43 so as to reflect and resonate on the optical path as shown in FIG. , the light is allowed to repeatedly pass through the optical paths within the waveguides 34a to 34d. Further, the mirror mounts 42 and 43 are provided with water passage holes 44a, 44b, 45a, and 45b at appropriate locations, respectively, and are connected to the cooling water passage hole 31a provided in the electrode base 31 of the waveguide body. Cooling water can be passed from the outside to the electrode base 31 through these water passage holes 44a, 44b, 45a, and 45c.

Note that 46 in the mirror mount 42 is an output hole for the laser beam LB, and is formed so that its central axis coincides with the optical axis of the output mirror 21.

With this configuration, the present device can have an optical path with high space utilization efficiency, and can also have a long optical path length to obtain high-output laser light.

That is, as mentioned above, in this device, the main optical path is formed along the four longitudinal ridge lines of the virtual rectangular parallelepiped, and each optical path is connected by a mirror.
The optical path length can be increased, and the utilization rate of the occupied space can also be increased.

In addition, in this device, a folding mirror that connects the intermediate optical path is fixed to the opposing surface of the holding table using a pair of reflecting mirrors, with the opposing surfaces opening at 90 degrees, and this is fixed to the mirror mounts 42 and 43. Since it is fixedly installed, once the optical axes of each mirror and waveguide are aligned and installed, there is no need to worry about optical axis misalignment due to vibration during transportation, and there is no need to adjust the optical axis later. In addition, the waveguide body has a hole through which the refrigerant passes, and this is used for cooling, which suppresses the heat generated by discharge, etc., and prevents the structure from expanding due to the heat generated during operation. The optical axis shift caused by these factors is also suppressed.

In addition, since the waveguide body is small compared to the possible optical path length, even if the outer casing 41 for gas filling that surrounds the waveguide body is relatively large compared to the waveguide body, the device will become too large. Since no interference occurs, the internal space can be enlarged, and the density distribution of the laser gas is less likely to change, so the laser output is stable.The RF system has a robust structure and can provide stable high-output laser light. A discharge lateral excitation guide type gas laser device is obtained.

It should be noted that the present invention is not limited to the embodiments described above and shown in the drawings, but can be implemented with appropriate modifications within the scope of the gist thereof. It may also be configured as shown in FIGS. 6 to 8.

That is, in FIG. 6, the electrode plates 32a and 32d, which were separated in FIG.
A, 34b and 34c, 34d are covered to simplify the structure. Also,
FIG. 7 shows a pair of electrode bases 71, 7 with an L-shaped cross section.
2, the electrode bases 71 and 72 are assembled to form a rectangular cylinder, and this rectangular cylinder is used as an electrode base main body 73.
Waveguides 34a and 34d are formed inside. Electrode plates 32a, 32b, 32c, and 32d are arranged on the inner facing surface of the electrode base body 73, respectively, with appropriate distances as in the case of FIG. Close the gap with the wall from both sides,
Dielectric plates 33a to 33f are provided to form the waveguides 34a to 34d and to electrically insulate the electrode plates 32a to 32d and the electrode base body 73.

The electrode base main body 73 having such a structure can also function as an outer casing of the waveguide main body, making the structure even simpler.

Note that the joint parts 74 and 75 of the electrode bases 71 and 72
It is necessary to have a sealed structure, and good results can be obtained by using electron beam welding or laser welding for this purpose, but in addition to these welding methods, it is recommended to use a joining method that does not leave thermal strain inside the material. You can also do it. In addition, 71a, 71b, 72a, 72
b is a hole through which the refrigerant passes.

FIG. 8 shows an example in which waveguides are formed at equal division angles, for example, in 60 increments on the circumference of a circle having an arbitrary radius within a certain size range.

That is, a circle is drawn from the central axis of the electrode base 81 on the four longitudinal sides of the rectangular block-shaped electrode base 81, and the circumference is divided into 60° increments, and the dielectric plate 82 is arranged so that waveguides are formed at the divided positions. and an electrode plate 83, and the basic structure is the same as that shown in FIG.

In the case of the configuration shown in FIG. 8, the number of waveguides is six, so folding multiplexing is further performed, and the length of the waveguide becomes longer. Note that 81a is a hole for coolant circulation.

Each of these methods makes it possible to further simplify the structure of the waveguide body or to extend the waveguide length.

Furthermore, in the above embodiments, the electrode base is cooled by circulating a coolant such as cooling water, but a cooling structure using a heat pipe, a semiconductor cooling element, etc. may also be used.

〔Effect of the invention〕

As described in detail above, the present invention provides a gas laser device in which electrode plates are separately disposed on at least one pair of opposing side wall surfaces of a block-shaped electrode base having a cooling means, and the electrode plates and the side wall surfaces are separated from each other. Dielectric plates facing each other are provided at appropriate intervals between them to form a plurality of waveguides that are open at both ends surrounded by the side wall surface of the electrode base, the electrode plate, and the dielectric plate. In this method, each waveguide is connected in series by installing a reflecting mirror with one of the reflecting optical axes aligned with the axis of the waveguide, and with the optical axis of the other reflecting mirror aligned with the reflecting mirror of the waveguide to be connected. Furthermore, at both ends of the series-connected waveguides, one is provided with a total reflection mirror, and the other is provided with a semi-transmission mirror, and the reflection mirrors are paired at the same end. The structure is such that the electrode base and the electrode plate are held by the same holding body, and a high frequency voltage is applied between the electrode base and the electrode plate to cause a discharge, thereby exciting light within the waveguide and generating laser light. Since the discharge distance is short and the frequency is high, high voltage is not required for discharge.In addition, multiple waveguides are provided on at least two opposing walls of the electrode base, and these are optically connected in series. Therefore, even if the device length is short, a long waveguide length can be obtained and high output can be obtained, and space utilization efficiency is also high.
Since the pair of reflecting mirrors are fixed to the same holder, they are resistant to mechanical vibrations and their optical axes will not shift, and since the electrode base is configured to be cooled, We have developed a waveguide-type gas laser device that has excellent features such as minimizing the effects of heat generation and suppressing misalignment between the optical axis and the center axis of the waveguide due to thermal expansion of the device to obtain highly stable laser light. can be provided.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the optical path configuration of the conventional method, Fig. 2 is a diagram for explaining the optical path configuration and the arrangement and structure of the mirrors of the device of the present invention, and Fig. 3 is the structure of the waveguide body in the device of the present invention. FIG. 4 is a perspective view showing the overall configuration of the present invention, FIG. 5 is a cross-sectional view of FIG. 4, and FIGS. 6 to 8 are other configuration examples of the waveguide body. FIG. 1, 21... Output mirror, 2, 22... Total reflection mirror, 3, 23a, 23b, 23c... Returning mirror, 31, 71, 72, 81... Electrode base, 31a, 71a, 71b, 72a, 72
b, 81a... hole, 32a, 32b, 32c, 3
2d, 61, 62, 83...electrode plate, 33a, ~
33f, 82...dielectric plate, 41...casing.

Claims (1)

[Claims] 1. In a gas laser device, electrode plates are arranged spaced apart from each other on at least one pair of opposing side wall surfaces of a block-shaped electrode base having a cooling means, and the electrode plates and the side wall surfaces are arranged facing each other at an appropriate interval. A dielectric plate is provided to form a plurality of waveguides with openings at both ends surrounded by the side wall surface of the electrode base, the electrode plate, and the dielectric plate, and one of the reflective optical axes is connected to the end of these waveguides. Each waveguide is connected in series by providing a reflecting mirror to match the axis of the waveguide, and by aligning the optical axis of the other reflecting mirror with the reflecting mirror of the waveguide to be connected. At both ends of the waveguides connected in series, a total reflection mirror that totally reflects the light is provided on one side, and a semi-transmission mirror is provided on the other side, and the reflecting mirrors are paired at the same end. The electrodes are arranged so as to be held by the same holding body, and a high frequency voltage is applied between the electrode base and the electrode plate to cause a discharge, thereby exciting the laser beam. Gas laser equipment.