JP2989296B2 - Microwave discharge excitation method for laser gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for exciting a laser gas by microwave discharge applied to a laser oscillator in a microwave region.

[0002]

2. Description of the Related Art A conventional laser device will be described with reference to FIGS.

A discharge tube 1 is inserted into a cylindrical cavity resonator 4 connected from a microwave oscillator 2 via a waveguide 3.
A total reflection mirror 5 and an output mirror 6 are provided at both ends. The microwave output from the microwave oscillator 2 propagates through the waveguide 3, is transmitted to the cylindrical cavity resonator 4, and the laser gas in the discharge tube 1 is discharge-excited by the electric field of the microwave. As a result, stimulated emission light from the laser gas medium is obtained, amplified by reciprocal reflection between the total reflection mirror 5 and the output mirror 6 constituting the optical resonator, and the laser light 7 transmitted through the output mirror 6 is extracted.

[0004]

SUMMARY OF THE INVENTION Discharge excitation of laser gas by microwave is described in Handy and Brandelik, J. Appl.
Phys., 49, 3753-3756 (1978). Is already known. However, when using a cavity filled with microwaves, it is possible to discharge-excit the laser medium, but as a standing wave of microwaves that can be formed in a normal cavity, TM is used.
As the microwave (Electromagnetic field) or the TE mode (Transverse Electric Mode) is mixed in a large number, the electromagnetic field of the microwave acting on the discharge becomes complicated and various waves, and the microwave electric field intensity is reduced. It is not constant in the pipe axis direction. Therefore,
Since the laser gas medium in the entire discharge tube cannot be excited by discharge, and the electric field of the discharge is concentrated in a local space in the discharge tube,
When the temperature of the generated discharge plasma rises, it is difficult to establish a population inversion of the energy level contributing to laser oscillation, so that there are disadvantages such as low laser output and oscillation efficiency.

When a cylindrical cavity resonator is used, the discharge tube 1
When the axial direction is the same as the direction of the electric field of the microwave, the electromagnetic field mode of the microwave is the TM mode, but various modes are generated depending on the inner diameter dimensions of the microwave oscillator 2 and the cylindrical cavity resonator 4. . FIG. 5 shows one example. As inferred from this electric field vector, in this device:
The distribution of the discharge indicates a mode of non-uniform discharge due to the higher-order mode of the microwave. For this reason, there is a disadvantage that the entire space inside the discharge tube cannot be used for discharge excitation of the laser gas medium.

In the microwave electromagnetic field mode, the electric field distribution in the axial direction of the discharge tube becomes uniform by adjusting the inner diameter of the cylindrical cavity resonator to the cutoff wavelength in the TM mode.
A method of forming a M _{01 0} mode, but the occurrence of the insertion and discharge plasma discharge tube for the case of discharge excitation laser gas, since the dielectric constant varies the resonance frequency of the TM ₀₁₀ mode is microwave oscillator Since the oscillation frequency deviates from the oscillation frequency, a uniform discharge cannot be obtained only by adjusting the inner diameter of the cylindrical cavity resonator to the cutoff wavelength of the TM mode.

Further, since the conventional laser oscillation device is configured as described above, in order to obtain a high output laser beam, it is necessary to use a long discharge tube because the volume of the laser gas must be increased. That is, it is necessary to increase the length of the cylindrical cavity resonator. In this case, TM ₀₁₀
Although the resonance frequency of the mode does not change, the longer the length of the cylindrical cavity resonator, the more the electromagnetic field mode of a short-wavelength microwave can coexist inside. That is, since the resonance frequency of the higher-order mode approaches that of the _TM010 mode, the electric field distribution becomes non-uniform in the axial direction, and the generated discharge has a disadvantage.

Further, when the laser is oscillated in a state where the discharge is non-uniform in the axial direction of the discharge tube, the temperature becomes higher than the plasma obtained by the discharge excitation of the DC discharge in the same discharge region, and the laser output and the oscillation efficiency are lower. There was a disadvantage of becoming.

[0009]

The present invention employs the following means to solve the above-mentioned problems.

That is, as a microwave excitation method for a laser gas, (1) a microwave oscillator, a cylindrical cavity resonator for introducing microwaves output from the microwave oscillator, and a microwave resonator provided in the cavity resonator In a laser oscillator having a discharge tube that generates a discharge by an electric field and an optical resonator having a total reflection mirror and an output mirror,
Only the resonance frequency of the TM ₀₁₀ mode of the electromagnetic field that generates a uniform discharge in the axial direction in the cavity resonator is made to match the frequency of the microwave oscillator, and the entire laser gas in the discharge tube is caused by a single resonance mode. It is a method of discharging
The dielectric constant of the discharge tube is ε and the volume of the discharge tube is V, Δf
From / f ₀ = 3.74 × 10 ⁻⁴ εV, the microwave electromagnetic field
Of the frequency change of _TM010 mode of
Using the deviation Δf of the resonance frequency with respect to the vibration frequency f ₀ ,
The inner diameter D of the cavity resonator is defined as D = √ (5.274 × 10
²⁰ ) / (f ₀ (1 + Δf / f ₀ )) .

[0011]

( 2 ) In the cylindrical cavity resonator according to claim 1, the length of the cavity is set to a predetermined value, and the length of the cavity is set to a value other than the _TM010 mode of the microwave field. A microwave discharge excitation method for a laser gas, wherein a resonance frequency is separated from an oscillation frequency of a microwave oscillator by at least a half width of an oscillation spectrum.

[0013]

According to the above means, only the _TM010 mode suitable for laser oscillation is formed in the cavity resonator, the laser gas medium in the discharge tube is uniformly discharged and excited, and the laser output and oscillation efficiency are improved.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS.

The parts described in the conventional example are assigned the same reference numerals and their explanation is omitted, and the parts related to the present invention will be mainly described.

In FIG. 1, the resonance frequency f of the electromagnetic field mode formed in the cylindrical cavity resonator 4 and the inner diameter D of the cavity resonator are shown.
And the relationship with the length L are given in FIG.
The resonance frequency is made to match the frequency of the microwave oscillator 2 so that only the ₀₁₀ mode is formed. Then, only the _TM010 mode having a uniform electric field in the axial direction is formed as shown in FIG. 2, so that the gas in the discharge tube 1 is uniformly excited and discharged. Therefore, efficient laser oscillation can be obtained.

In a cavity resonator 4 having a discharge tube 1, TM ₀₁₀
In order to form only the mode, the inner diameter D is determined as follows.

That is, the deviation Δf of the resonance frequency caused by the insertion of the discharge tube (volume V) which is a dielectric into the cavity resonator and the deviation of the internal dielectric constant ε due to the generation of discharge plasma.
Is obtained from the following equation (1), and its inner diameter D is obtained from the equation (2).

Δf / f ₀ = 3.74 × 10 ⁻⁴ εV (1) D = √ ( 5.274 × 10 ²⁰ ) / (f ₀ (1 + Δf / f ₀₎ TM)) ... (2) in this embodiment of the above equation in order to form a TM ₀₁₀ mode 2.450MHz tailored to the oscillation frequency of the microwave oscillator 2 (half-value width 20 MHz), and D = 8.6 cm, close L = 20 cm so that the resonance frequency of the ₀₁₁ mode is 2,570 MHz (half-width 20 MHz) and the frequency of the oscillator is sufficiently separated. In this case, the laser output and the oscillation efficiency are D = 9. The results are shown in Table 1 together with the case of 4 cm (uncorrected).

[0020]

[Table 1]

Table 1 shows that the electric field is uniform and the oscillation efficiency is improved. On the other hand, when the inner diameter of the cylindrical cavity resonator 4 is set from the cutoff frequency of the TM mode of the microwave in the cylindrical waveguide (D = 9.4 cm), the discharge tube into the cylindrical cavity resonator and The deviation of the resonance frequency caused by the change of the dielectric constant due to the insertion of the discharge plasma, etc., causes the microwave frequency and the resonance frequency of the _TM010 mode to be inconsistent, and the electromagnetic field mode having a resonance frequency close to the microwave frequency This induces a discharge of the laser gas in the discharge tube. In this case, since the electromagnetic field is a higher-order mode for TM or TE, the distribution of discharge becomes uneven, the entire laser gas is not excited by discharge, and the laser output and oscillation efficiency are low.

Further, when only the inner diameter of the cylindrical cavity resonator is set from the above equation and the length of the cylinder is L = 50 cm, TM
Close to the resonance frequency of the ₀₁₀ mode becomes mixed discharge of the discharge or TM ₀₁₀ mode by the electromagnetic field mode,
In each case, the laser gas in the discharge tube becomes non-uniform discharge, and as shown in Table 1, the laser output and the oscillation efficiency decrease.

[0023]

As described above, according to the present invention, in a laser device having a discharge tube, a uniform discharge of the laser gas can be generated in the axial direction of the discharge tube. Discharge excitation of the laser gas in the discharge tube installed in the vessel can be effectively performed.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is an operation explanatory view of the embodiment.

FIG. 3 is an operation explanatory view of the embodiment.

FIG. 4 is a configuration diagram of a conventional example.

FIG. 5 is an operation explanatory view of the conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Discharge tube 2 Microwave oscillator 3 Waveguide 4 Cylindrical cavity resonator 5 Total reflection mirror 6 Output mirror 7 Laser light 8 Electric field vector

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01S 3/097

Claims (2)

(57) [Claims] 1. A microwave oscillator, a cylindrical cavity resonator for introducing microwaves output from the microwave oscillator, a discharge tube provided in the cavity resonator and generating a discharge by an electric field, In a laser oscillator comprising an optical resonator having a total reflection mirror and an output mirror, a T of an electromagnetic field for generating a uniform discharge in an axial direction in the cavity resonator.
A method in which only the resonance frequency of the _M010 mode is matched with the frequency of the microwave oscillator, and the entire laser gas in the discharge tube is discharged by a single resonance mode.
Δf / f _{0 where} ε is the dielectric constant of the electric tube and V is the volume of the discharge tube.
= 3.74 × 10 ⁻⁴ εV, TM of microwave electromagnetic field
Estimate the frequency change of ₀₁₀ mode,
Using the deviation Δf of the resonance frequency with respect to the number f ₀ ,
The inner diameter D of the body resonator is calculated as follows: D = √ (5.274 × 10 ²⁰ ) /
(F ₀ (1 + Δf / f ₀ )) A microwave discharge excitation method for a laser gas. 2. The cylindrical cavity according to claim 1, wherein the length of the cavity is set to a predetermined value, and resonance in a microwave electromagnetic mode other than the _TM010 mode of the microwave electromagnetic field is performed. A microwave discharge excitation method for a laser gas, wherein the frequency is separated from the oscillation frequency of a microwave oscillator by at least a half width of an oscillation spectrum.