JP2752517B2 - Laser discharge tube - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a laser discharge tube used for a laser oscillator, particularly to a laser discharge tube for preventing dielectric breakdown of an electrode provided on an outer periphery of a tube wall.

BACKGROUND ART In a discharge tube of a laser oscillator, a high voltage is applied to generate a discharge, and the discharge excites a laser gas to output a laser beam to the outside. By the way, the high voltage is applied to an electrode provided by being adhered to the outer periphery of the tube wall of the discharge tube,
Discharge is performed between electrodes facing each other across the discharge tube. Therefore, the normal discharge is performed in a region determined by the width of the electrode.

However, very high frequency voltages (eg, 40
(00 volts), a dielectric breakdown may occur between the electrodes other than between the electrodes, and corona discharge may occur. This corona discharge is likely to occur in a portion where the discharge tube temperature becomes high, for example, on the downstream side of the laser gas flowing in the discharge tube. In addition, the deterioration of the electrode material is rapidly accelerated.

Incidentally, silver having good conductivity is generally used for the electrode material. The electrode is formed by mounting the silver on the outer wall of the discharge tube by metallizing or the like. When a high voltage is applied to this electrode, a strong electric field distribution occurs at the edge of the electrode, and corona discharge occurs. In addition, the corona discharge is lifted due to thermal distortion or the like of the electrode, and also occurs in the air gap when an air gap is formed. The corona discharge runs along the outer wall surface of the discharge tube once, and enters the discharge tube at a position several millimeters away from the electrode. At that time, silver elutes in opposition to the water component, and the eluted silver grows from the electrode along the outer wall of the discharge tube in a dendritic manner, and the discharge tube wall around the electrode extends several centimeters. It will cover with width. When such a phenomenon that silver of the electrode material moves (migration) occurs, the withstand voltage further decreases, corona discharge is more likely to occur, and outflow of the electrode material, deterioration of the electrode, and the like become more remarkable. . Further, since the periphery of the electrode is covered with the melted silver, the width of the electrode is widened and the electrical characteristics are changed, so that the life of the discharge tube is shortened. The appearance of the discharge tube also becomes poor.

In order to prevent the above-described corona discharge, the voltage applied to the electrode may be reduced. However, if this is done, the injection power decreases, and it becomes impossible to cope with laser processing requiring power. In addition, since corona discharge is more likely to occur as the temperature increases, there is a method of lowering the electrode temperature by attaching a heat-releasing plate to the electrode.However, downstream of the laser gas where the discharge tube temperature increases, the corona discharge also occurs. The occurrence cannot be prevented. Further, the temperature can be lowered by lowering the applied voltage, but also in this case, as described above, the injection power is reduced, and it is impossible to cope with laser processing requiring power.

DISCLOSURE OF THE INVENTION The present invention has been made in view of such a point,
An object of the present invention is to provide a laser discharge tube capable of preventing outflow and separation of an electrode material due to corona discharge, deterioration of an electrode, and the like.

Another object of the present invention is to provide a laser discharge tube capable of improving the heat radiation characteristics and insulation resistance of the electrode and increasing the injection power.

In the present invention, in order to solve the above-mentioned problems, in a laser discharge tube that generates a discharge by an applied high-frequency voltage and excites a laser gas, an electrode mounted on the outer periphery of a tube wall and a low melting point mounted on the electrode are provided. A laser discharge tube, comprising: a dielectric layer formed of a ceramic material having a low thermal expansion coefficient or a negative thermal expansion coefficient using glass as a binder.

A dielectric is coated or mounted on the electrode mounted on the outer periphery of the tube wall so as to cover the electrode to form a dielectric layer. With this dielectric layer, it is possible to prevent the occurrence of corona discharge that has been conventionally induced at the electrode end.

In addition, by using a ceramic material having a low thermal expansion coefficient or a negative thermal expansion coefficient with a low melting point glass as a binder for the dielectric layer, peeling, deterioration of the electrode, and the like can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a configuration of a laser discharge tube of the present invention, and FIG. 2 is a diagram schematically showing a configuration of a laser oscillator using the laser discharge tube of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 2 is a diagram schematically showing a configuration of a laser oscillator using the laser discharge tube of the present invention. The laser discharge tube 1 is made of a dielectric material (for example, quartz glass), and is a pipe having a circular cross section. On the outer peripheral surface of the laser discharge tube 1, two electrode portions 2, 3 are spirally provided at the same pitch. The electrode section 2 is composed of an electrode 21 and a dielectric layer 22, and the electrode section 3 is composed of an electrode 31 and a dielectric layer 32 in the same manner. The details will be described later. A laser gas 10 flows through the laser discharge tube 1 in the tube axis direction indicated by an arrow, and a high-frequency power supply (not shown)
When a high-frequency voltage is applied between the electrodes 21 and 31, a discharge occurs between the electrodes facing each other across the discharge tube 1 in the laser discharge tube 1, and the laser gas 10 is excited. A total reflection mirror 4 and an output coupling mirror 5 are provided at both ends of the laser discharge tube 1 to constitute a Fabry-Perot resonator, which oscillates light emitted from the excited laser gas molecules and partially outputs the light. The laser light 11 is output from the coupling mirror 5. The laser beam 11 is applied to the work to perform laser processing. The laser discharge tube 1 can be made of not only quartz glass but also other dielectric materials (for example, alumina and aluminum titanate) which are resistant to dielectric breakdown. Also,
Although a spiral electrode is provided in the laser discharge tube 1, a plate-shaped electrode may be provided.

FIG. 1 shows the configuration of the laser discharge tube of the present invention, and is a cross-sectional view taken along line XX of FIG. Outer surface 1A of tube wall of laser discharge tube 1
Are provided with the electrode portions 2 and 3 as described above. The electrodes 21 and 31 of the electrode portions 2 and 3 are formed by mounting silver as a dielectric on the outer peripheral surface 1A of the tube wall by metallizing. A dielectric layer 22 is formed so as to cover the electrodes 21 and 31.
And 32 are formed. The dielectric layers 22 and 32 are attached to the electrodes 21 and 31 on the outer peripheral surface 1A of the tube wall by spraying, coating, baking or the like of a dielectric material such as a ceramic material, glass, resin, or by bonding a separately molded dielectric material by bonding. The thickness is formed to be about 0.1 mm to 5 mm.

Here, a case will be described in which the dielectric layers 22 and 32 are made of a ceramic material having a body thermal expansion coefficient or a negative thermal expansion coefficient using low-melting glass as a binder. Typical lead oxide (PbO.B ₂ O ₃ ) is used as low melting glass, and aluminum titanate (Al ₂ TiO ₅ ), boron nitride (BN) and silicon nitride (Si ₃ N ₄ ) are used as ceramic materials. use.

Lead oxide (PbO.B ₂ O ₃ ) has a melting point of about 400 ° C. to 450 ° C. and has a lower melting point than silver forming the electrodes 21 and 31. Are suitable.
In addition, this lead oxide is used in the initial stage in which the electrodes 21 and 31 are lifted by thermal strain and air gap discharge occurs, and
It also has the function of melting itself and causing self-renewal by flowing into the air gap before the melt-down occurs. The mixing ratio of lead oxide to the whole is 50 to 90% by weight.

Aluminum titanate and boron nitride have a negative coefficient of thermal expansion, and play a role in reducing the overall coefficient of thermal expansion when mixed with lead oxide. The mixing ratio to the whole is adjusted so that the coefficient of thermal expansion is substantially equal to the coefficient of thermal expansion of the laser discharge tube 1. For example, aluminum titanate is 18 wt% and boron nitride is 5 wt%. Also, since aluminum titanate and boron nitride have a higher thermal conductivity than low-melting glass, the overall thermal conductivity also increases. In particular, since the thermal conductivity of boron nitride is large, the heat dissipation is greatly improved by the mixing of boron nitride. In addition, a small amount of silicon nitride (for example, 2w
t%) by adding ceramic material to the discharge tube 1 for laser.
This improves the ease of application when applied to the surface. In order to obtain the same effect, silicon carbide can be used instead of silicon nitride. The above-mentioned lead oxide, aluminum titanate, boron nitride and silicon nitride are mixed together with a solvent, applied as a ceramic paint to the electrodes 21 and 31 of the laser discharge tube 1, and further fired in a thermostatic layer. The firing conditions are, for example, 450 ° C. × 30 min.

The electrodes 21 and 31 are completely covered by the ceramic mounting layers (dielectric layers) 22 and 32 thus manufactured. For this reason, silver does not come into contact with water and react and melt. Conventionally, the electrodes 21 and 31 and the tube wall outer peripheral surface 1A
The air gap portion interposed between the air gap portion and the air gap portion disappears, and there is no room for the corona discharge induced in the air gap portion to occur. Further, a discharge tube 1 for laser and an electrode
Since the floating air gap due to the thermal strain between 21 and 31 is also self-regenerated, there is no room for corona discharge to occur at this point. Therefore, the dissolution and peeling of silver forming the electrodes 21 and 31 and the deterioration of the electrodes 21 and 31 can be prevented, and the life of the laser discharge tube 1 has been improved by 10 times or more. In addition, the characteristics are not deteriorated (changed) by covering the periphery of the electrode with the dissolved silver. The appearance of the discharge tube does not deteriorate.

Further, since the ceramic mounting layers 22 and 32 are adjusted so that their thermal expansion coefficients are substantially equal to those of the laser discharge tube 1, the ceramic mounting layers 22 and 32 and the laser discharge tube 1 are adjusted.
And the thermal strain generated between the ceramic mounting layers 22 and 32 does not peel off due to the thermal strain. Therefore, also in this respect, the life of the laser discharge tube 1 is greatly improved.

Also, by using a material having high thermal conductivity and high insulation resistance for the ceramic mounting layers 22 and 32, the electrodes 21 and
The heat radiation characteristics and insulation resistance of the semiconductor device 31 can be improved, and the injection power (injection power), which has been suppressed conventionally, can be increased. In the improvement of the heat radiation characteristics, the laser oscillation output at the same injection power was, for example, 1570 W, but the discharge tube for laser of the present invention was able to increase by about 15% to 1770 W. The insulation resistance between the electrodes is increased by a factor of five. The ceramic mounting layers 22 and 32 can withstand injection powers up to 400 ° C. In addition, it was able to withstand the rapid cooling test at -200 ° C to 400 ° C. More ultimately, 15
Even when the temperature reached 00 ° C., the self-regeneration function could be maintained.

In the above description, aluminum titanate and boron nitride are used as ceramic materials having a negative coefficient of thermal expansion. However, other ceramic materials, for example, lead titanate can also be used. Further, although aluminum titanate and boron nitride are used as a mixture, only one of aluminum titanate and boron nitride may be used.

Further, the same effect can be obtained by using not only a ceramic material having a negative coefficient of thermal expansion but also a ceramic material having a low coefficient of thermal expansion.

Further, for example, a titanium composite oxide (TiO, Al ₂ TiO ₅ , M
A ceramic material mainly composed of gTiO ₃ or a composite ceramic material of the titanium composite oxide and alumina, magnesia, boron nitride, or the like may be used as the ceramic paint. In this case, as the binder, silicon or tyranopolymer (Si-C) can be used in addition to the lead oxide. When using a composite ceramic material of titanium composite oxide and alumina, magnesia, boron nitride, etc., by adjusting the blend of titanium composite oxide with alumina, magnesia, boron nitride, etc., a low coefficient of thermal expansion and high thermal conductivity can be obtained. It is possible to obtain a ceramic material having a high modulus.

Further, in the above description, silver is used for the electrode, but another conductive material (for example, gold) may be used.

As described above, in the present invention, since the dielectric is mounted on the electrode of the laser discharge tube, the electrode is completely covered by the dielectric layer. For this reason, the air gap portion conventionally interposed between the electrode and the outer peripheral surface of the tube wall is also eliminated, and there is no room for the corona discharge induced in the air gap portion in combination with the self-regeneration function. Therefore, the dissolution of the electrode material, the deterioration of the electrode, and the like can be prevented.

In addition, there is no deterioration (change) in characteristics due to the periphery of the electrode being covered with the dissolved silver, and the life can be extended.

Furthermore, by using a material having high thermal conductivity and high insulation resistance for the dielectric layer, it is possible to improve the heat radiation characteristics and insulation resistance of the electrodes, and to increase the injection power, which was conventionally suppressed. it can.

In particular, since the dielectric layer is made of a ceramic material having a low thermal expansion coefficient or a negative thermal expansion coefficient using a low-melting glass as a binder, the coefficient of thermal expansion is substantially equal to that of the laser discharge tube, and the dielectric layer is insulated from the laser discharge tube Thermal strain with the body layer is extremely small, and the dielectric layer does not peel off due to the thermal strain.

Continuation of the front page (56) References JP-A-2-23684 (JP, A) JP-A-63-24686 (JP, A) JP-A-64-66983 (JP, A) JP-A-63-95644 (JP) , A) JP-A-2-207578 (JP, A) JP-A-2-145486 (JP, A) Jikken Sho 54-36455 (JP, Y2)

Claims (9)

(57) [Claims] 1. A laser discharge tube for generating a discharge by an applied high-frequency voltage to excite a laser gas, comprising: an electrode mounted on an outer periphery of a tube wall; and a low thermal expansion mounted on the electrode and using low melting glass as a binder. And a dielectric layer made of a ceramic material having a coefficient or a negative coefficient of thermal expansion. 2. The laser discharge tube according to claim 1, wherein said ceramic material is a titanium composite oxide. 3. The titanium composite oxide is aluminum titanate or lead titanate.
The discharge tube for a laser according to the above. 4. The laser discharge tube according to claim 1, wherein said ceramic material is boron nitride. 5. The laser discharge tube according to claim 1, wherein said ceramic material is a titanium composite oxide and boron nitride. 6. A laser discharge tube according to claim 2, wherein said ceramic material is mixed with silicon nitride or silicon carbide. 7. The laser discharge tube according to claim 1, wherein the mixing ratio of the binder is 50 to 90% by weight. 8. The laser discharge tube according to claim 2, wherein said ceramic material is a composite ceramic material comprising a titanium composite oxide, alumina, magnesia, and boron nitride. 9. A laser discharge tube for generating a discharge by a high-frequency voltage applied to excite a laser gas, comprising: an electrode mounted on an outer periphery of a tube wall; and an electrode mounted on the electrode and having a temperature lower than a melting point of the electrode. And a dielectric layer made of a material having a melting point temperature higher than a required heat-resistant temperature of the laser discharge.