JPH05206552A - Gas laser device - Google Patents

Abstract

PURPOSE:To enable a gas laser device to output stable laser light pulses without increasing gas laser medium in speed when the laser device is enhanced in pulse repetition rate. CONSTITUTION:A gas laser device is equipped with a fan 4 which is located inside a discharge chamber 1 to enable laser gas medium to circulate through a discharge space between main electrodes composed of a cathode 2 and an anode 3 and pin electrodes 8 and 9 which are provided along the side of the main electrodes and between the discharge side of the fan 4 and the main electrodes 2 and 3 to previously pre-ionize the discharge space before the main discharge starts between the main electrodes 2 and 3. Letting the width of the discharge region be L1, the distance between the axial center of the pin electrodes and the boundary of the main discharge region be L2, the flow velocity of gas laser medium be V, and T the pulse repetition period of a main discharge be T, L1, L2, V, and T satisfy formulas, L2>L1 and (L2/T)>V>{(L1+ L2)/2T}.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas laser device having a structure in which a main discharge is generated after pre-ionizing a discharge space.

[0002]

_2. Description of the Related Art Generally, in a gas laser device of a lateral excitation type such as a CO ₂ laser or an excimer laser which is operated under a so-called high gas pressure, in order to stably ignite a main discharge for exciting a gas laser medium in a discharge space portion. In order to pre-ionize the discharge space portion by pre-discharging prior to the main discharge ignited between a pair of main electrodes composed of a cathode and an anode, a pre-ionizing means composed of pin electrodes is provided. .. That is, conventionally, as shown in FIG. 3, two electrodes are provided on both sides in the width direction of the main electrode composed of the cathode a and the anode b.
A plurality of sets of pin electrodes c that form a set are provided at predetermined intervals along the longitudinal direction of the main electrode, and ultraviolet rays generated by igniting a discharge between the tips of the pin electrodes c of each set are used. The discharge space S is preionized.

It has been confirmed by experiments that in the gas laser device having such a structure, the oscillation efficiency of the laser oscillation output decreases as the repetition frequency of the pulse discharge increases, and finally the laser oscillation stops. This tendency was likely to occur under the condition that the gas flow velocity was low with respect to repeated discharge. From the discharge light emission generated between the main electrodes a and b, when observing the place where the discharge occurs, when the laser oscillation efficiency is high, the main discharge is generated at the main electrode as shown by G in FIG. It occurs with a predetermined width dimension in the central portion in the width direction between the constituent cathode a and anode b.

However, if the number of pulse repetitions increases with respect to the flow velocity of the gas laser medium, discharge may occur in an arc shape also on the downstream side in the width direction between the cathode a and the anode b, as indicated by P in FIG. Was observed. The luminance of the arc-shaped discharge P is stronger than that of the main discharge G, and it is considered that the arc discharge is locally concentrated. It can be inferred that this arc discharge is generated by the gas laser medium that has undergone the main discharge G being accelerated by ionization by being irradiated with ultraviolet rays generated at the pin electrode c on the downstream side during the preionization in which the next pulse discharge occurs. When such arc discharge P occurs, laser oscillation is stopped or the laser output is significantly reduced.

By the way, in general, the flow of the gas laser medium sweeps the gas laser medium that has experienced the main discharge G from the discharge space S until the next main discharge G occurs once the main discharge G occurs. , To replace a new cooled gas laser medium. As the degree of replacement of the gas laser medium, the next main discharge G is based on the discharge width L ₁ of the main discharge G generated in the discharge space S.
The magnification is defined as the gas exchange rate (CR value) depending on how many times the width of the main discharge G the gas laser medium is flown into at the central portion in the width direction of the main electrodes a and b. It has been confirmed that the laser oscillation efficiency of the subsequent pulse is higher when the gas laser medium is made faster to increase the CR value and the gas laser medium that has undergone the main discharge is allowed to flow out to the place where the arc discharge P does not occur.

However, in order to increase the flow velocity of the gas laser medium, it is necessary to increase the capacity of the blower,
Along with that, the power consumption rapidly increases, which causes a significant increase in running cost. Further, high-speed air blowing may lead to an increase in the size of the air blower and an increase in noise.

[0007]

As described above, if the flow velocity of the gas laser medium is increased to prevent the occurrence of arc discharge between the main electrodes, the running cost may be increased due to a rapid increase in power consumption, This may lead to an increase in the size of the device and an increase in noise.

The present invention has been made in view of the above circumstances. An object of the present invention is to prevent the occurrence of arc discharge between main electrodes without increasing the flow velocity of the gas laser medium. To provide.

[0009]

In order to solve the above-mentioned problems, a first invention is to provide a discharge chamber in which a gas laser medium is enclosed, and a main discharge which is arranged so as to face each other in the discharge chamber. A main electrode consisting of a cathode and an anode for exciting the gas laser medium, a circulation means for circulating the gas laser medium through a discharge space between the cathode and the anode, a discharge side of the circulation means and the main electrode. And a pin electrode that is provided along the side of the main electrode and pre-ionizes the discharge space prior to the main discharge ignited by the main electrode, and the width dimension of the main discharge region is When L ₁ , the distance from the axis of the pin electrode to the boundary of the main discharge region is L ₂ , the flow velocity of the gas laser medium is V, and the pulse repetition period of the main discharge is T, set L ₂ > L ₁ . With _{(L 2 / T)> V} > {(L 1 +
L ₂ ) / 2T} is set.

A second aspect of the invention comprises a discharge chamber in which a gas laser medium is enclosed, and a cathode and an anode which are arranged facing each other in the discharge chamber and excite the gas laser medium by a main discharge generated therebetween. A main electrode, a circulation means for circulating the gas laser medium through a discharge space between the cathode and the anode, and a side portion of the main electrode provided between the discharge side of the circulation means and the main electrode. And a pin electrode for pre-ionizing the discharge space prior to the main discharge ignited by the main electrode, the width dimension of the main discharge region is L ₁ , and the main discharge is from the axial center of the pin electrode. When the distance to the boundary of the region is L ₂ , the flow velocity of the gas laser medium is V, and the pulse repetition period of the main discharge is T, L
₂ > L ₁ and the value (CR value) determined by {V · T / L ₁ } is set to 1 or more and 5 or less.

[0011]

According to the first and second aspects of the invention, when the number of repetitions of the pulse discharge is increased, the arc discharge is generated between the cathode and the anode without increasing the flow velocity of the gas laser medium more than necessary. It is possible to prevent the laser output from being lowered due to the occurrence of the noise or the main discharge becoming unstable.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS.
Will be described.

The gas laser device shown in FIG. 1 comprises a cylindrical discharge chamber 1 in which a gas laser medium is enclosed.
In the discharge chamber 1, a cathode 2 and an anode 3 forming a main electrode are spaced apart and opposed to each other, and the longitudinal direction is arranged along the axial direction of the discharge chamber 1. A blower 4 for circulating the gas laser medium in the discharge chamber 1 through the discharge space S between the cathode 2 and the anode 3 in the direction of the arrow in the figure, and heat exchange for cooling the gas laser medium circulated by the blower 4. A container 5 and a filter 6 for removing dust from the gas laser medium are arranged.

A base end portion is provided on one side of the cathode 2 between the discharge side of the blower 4 and the cathode 2 (this side is the upstream side where the gas laser medium flows into the discharge space S). A plurality of upper pin electrodes 8 connected to the first peaking capacitor 7 are vertically provided at predetermined intervals along the longitudinal direction of the cathode 2. A lower pin electrode 9 is disposed on one side of the anode 3 facing the upper pin electrode 8 and a tip of the lower pin electrode 9 is disposed at a tip of the upper pin electrode 8 via a discharge gap.

The first peaking capacitor 7 is electrically connected to the cathode 2, and the lower pin electrode 9 is electrically connected to the anode 3. Further, the cathode 2
A second peaking capacitor 11 is connected between the anode 3 and the anode 3.

The cathode 2 is connected to the negative side of a DC high voltage power source 12, and the anode 3 is a thyratron switch 13.
It is connected to the positive side of the DC high-voltage power supply 12 via. A main capacitor 14 is connected between the negative side and the positive side of the DC high-voltage power supply 12.

The drive source 4a of the blower 4 is a speed controller 1
It is connected via 5 to a clock pulse generator 16. When a clock pulse is generated by the clock pulse generator 16, an inverter frequency for driving the blower 4 is determined according to the frequency, and the blower 4 is driven.
Are driven to rotate at a predetermined speed. That is, the flow velocity of the gas laser medium is controlled. The thyratron switch 13 is an element drive circuit 17
And a clock pulse generator 16 via a switch 18. When the switch 18 is closed, the thyratron switch 13 is closed by the element drive circuit 17 at a frequency according to the clock pulse from the clock pulse generator 16.

When the thyratron switch 13 is closed, the electric charge stored in the main capacitor 14 becomes the first,
The process moves to the second peaking capacitors 7 and 11. First
Since the electric charges transferred to the peaking capacitor 7 pass through the gap between the upper pin electrode 8 and the lower pin electrode 9, the arc discharge is ignited in this gap to generate ultraviolet rays. When the discharge space S is pre-ionized by the ultraviolet rays, the main discharge G is ignited between the cathode 2 and the anode 3, and the main discharge G excites the gas laser medium to generate laser light.

In the gas laser device having the above structure, the width dimension of the main discharge region ignited between the cathode 2 and the anode 3 is L.
_{1. When} the distance from the axial center of the pin electrodes 8 and 9 to the boundary of the main discharge region is L ₂ , it is set to (L ₂ > L ₁ ). When the flow velocity of the gas laser medium is V and the pulse repetition period of the main discharge is T, the flow velocity V of the gas laser medium is (L ₂ / T)>V> {(L ₁ + L ₂ ) / 2T} (1 ) The flow velocity V and the period T are set by the clock pulse generator 16 so as to be in the range of the following equation.

Under these conditions, the gas laser medium that has undergone preliminary discharge between the pair of pin electrodes 8 and 9 is
When the next subsequent pulse is generated, it does not reach the discharge width L ₁ of the discharge space portion 8 located at the distance L ₂ from the pin electrodes 8 and 9.
Moreover, the gas laser medium that has experienced the main discharge G in the discharge space S has flowed to the downstream side of the main discharge region. Therefore, because of these things, the cathode 2 and the anode 3 are
Between and, the main discharge is ignited in a stable state.

When the number of pulse repetitions changes,
Accordingly, if the velocity range of the gas laser medium is changed based on the above equation (1), the subsequent pulse is generated before the gas laser medium that has undergone the preliminary discharge flows into the main discharge region of the discharge space S, so that the preliminary discharge is performed. The main discharge does not become unstable due to the gas laser medium that has experienced.

By providing the above-mentioned pin electrodes 8 and 9 only on the upstream side, the gas laser medium which has experienced the main discharge and has flowed on the downstream side has the upstream pin electrode 8 at the time of preionization prior to the next subsequent pulse. , 9 is not irradiated with ultraviolet rays generated by the spark discharge in the vicinity of the main discharge G.
Moreover, since there is no pin electrode on the downstream side, it is not irradiated with ultraviolet rays. Therefore, the arc-shaped arc discharge P is generated by irradiating the gas laser medium, which has undergone the main discharge as in the conventional case, with ultraviolet rays between the cathode 2 and the anode 3 on the downstream side of the discharge space S.
Is prevented from occurring.

Further, since the pin electrodes 8 and 9 are provided only on the upstream side of the discharge space S and not on the downstream side,
Unlike the conventional case, the gas laser medium that has undergone the main discharge at the time of preionization does not flow between the pin electrodes on the downstream side to lower the dielectric breakdown voltage and reduce the generation amount of ultraviolet rays.
That is, according to the present invention, the fresh gas laser medium is always circulated sufficiently between the pin electrodes 8 and 9 on the upstream side and the fresh gas laser medium circulates, so that the dielectric breakdown voltage can be maintained high and the ultraviolet rays can be sufficiently emitted to the high repetition region. Can be generated. As a result, the main discharge and eventually the laser oscillation can be stabilized.

For example, if L ₁ is 10 mm, L ₂ is 35 mm, and the period T is 0.2 ms (5 kHz), then from the above equation (1),
_{(L 2 /T)=35/0.2 = 157 m /} s, (L 1 + L 2) /
Since 2T = 10 + 35/2 × 0.2 = 112.5 m / s, if the velocity of the gas laser medium is set in the range of 50 to 157 m / s, the main discharge can be stably ignited. In other words, even if the repetition rate of laser oscillation is increased to 5 kHz, the CR value is 2.25.
~ 3.5. When L ₂ = 2L ₁ , CR value is 1.5-
2 and the speed of a given gas laser medium is 75-100 m /
s, and the speed of the gas laser medium does not have to be so high.

Regardless of the flow velocity of the gas laser medium according to the above formula (1), the above main discharge width L ₁ is used as a reference and the above main discharge is ignited until the next main discharge is ignited. A value determined by how many times the width of the main discharge width L ₁ the gas laser medium is poured into, that is, {V · T / L ₁ }
The CR value, which is a value determined by, may be set as a reference. That is, when (L ₂ > L ₁ ), the pin electrodes 8 and 9 are provided only on the upstream side, and when L ₂ = 4L ₁ , the gas laser medium that has undergone preliminary ionization discharge in the pin electrodes 8 and 9 is in the main discharge region. In the case of the structure to reach, by setting the flow velocity V according to the cycle T so that the CR value becomes 4 to 2.5, it is possible to prevent the main discharge from becoming unstable due to the gas laser medium that has undergone preionization.

The value of {V · T / L ₁ } is not limited to 4, and may be set to 1 or more and 5 or less. In this case, the cycle T
The gas laser medium that has undergone preliminary ionization may not exist in the main discharge region when the main discharge is ignited between the cathode 2 and the anode 3 by setting L ₂ and V according to the above. C
When the R value is set in the range of 1 to 5, the flow velocity of the gas laser medium does not need to be so large as in the above-described embodiment.

[0027]

As described above, according to the present invention, the next pulse oscillation is generated before the gas laser medium that has undergone the preliminary discharge reaches the main discharge region of the discharge space, and the discharge space is preliminary prepared. A pin electrode for ionization is provided only on the upstream side in the flow direction of the gas laser medium so that the gas laser medium that has undergone the main discharge is not excited from the gas in the main discharge space by the ultraviolet rays for preionization.

Therefore, the gas laser medium that has undergone the preliminary discharge is not excited in the main discharge region and the main discharge is not unstable, and the gas laser medium that has undergone the main discharge is not exposed to ultraviolet rays for preionization on the downstream side. Since the laser beam is excited by the laser beam and the arc discharge does not occur, the laser oscillation can be stably performed even if the pulse repetition rate is increased without increasing the flow velocity of the gas laser medium.

[Brief description of drawings]

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

FIG. 2 is an enlarged view of a main electrode portion.

FIG. 3 is an explanatory diagram of a conventional discharge generation state between main electrodes.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Discharge chamber, 2 ... Cathode (main electrode), 3 ... Anode (main electrode), 4 ... Blower, 8 ... Upper pin electrode, 9 ... Lower pin electrode, 15 ... Speed control part, 16 ... Clock pulse generator, 17 ... Element drive circuit.

Claims (2)

[Claims] 1. A discharge chamber in which a gas laser medium is enclosed, and a main electrode composed of a cathode and an anode, which are arranged facing each other in the discharge chamber and excite the gas laser medium by a main discharge generated therebetween. Circulating means for circulating the gas laser medium through the discharge space between the cathode and the anode, and the main electrode provided between the discharge side of the circulating means and the main electrode along the side of the main electrode. A pin electrode for pre-ionizing the discharge space prior to the main discharge being fired at
_1, the distance L ₂ to the axial center boundary of the main discharge region of the pin electrodes, when the flow rate of the gas laser medium V, and the pulse repetition period of the main discharge is T, is set to L _2> L ₁ Together with (L ₂ /) T>V> {(L ₁ + L ₂ ).
/ 2T} is set. 2. A discharge chamber in which a gas laser medium is enclosed, and a main electrode composed of a cathode and an anode which are arranged facing each other in the discharge chamber and excite the gas laser medium by a main discharge generated therebetween. Circulating means for circulating the gas laser medium through the discharge space between the cathode and the anode, and the main electrode provided between the discharge side of the circulating means and the main electrode along the side of the main electrode. A pin electrode for pre-ionizing the discharge space prior to the main discharge being fired at
_1, the distance L ₂ to the axial center boundary of the main discharge region of the pin electrodes, when the flow rate of the gas laser medium V, and the pulse repetition period of the main discharge is T, is set to L _2> L ₁ together with the values determined by the _{{V · T / L 1}} (CR
Value) is set to 1 or more and 5 or less.