JP2942033B2 - Discharge pump laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge excitation pulse laser device, and more particularly to a preionization timing thereof.

[0002]

2. Description of the Related Art In order to excite a laser efficiently by discharge, it is essential to generate a uniform main discharge. For this reason, pre-ionization for generating electrons serving as seeds of the discharge in the discharge field is usually performed before the occurrence of the main discharge. FIG. 8 is an excitation circuit configuration diagram of a conventional discharge excitation pulse laser device cited, for example, from a literature ("Development of Excimer Laser and Its Application Techniques / Examples", edited by Shuntaro Watanabe, Applied Technology Publishing, p. 17). Generally, the circuit shown in FIG. 1 is called a capacitance transfer type circuit. In the figure, 1 is a first main electrode, and 2 is a second main electrode. Reference numeral 3 denotes a power supply terminal provided for supplying a high voltage to the excitation circuit, 4 denotes a storage capacitor, and 5 denotes a peaking capacitor. Reference numeral 6 denotes a switch, 7 denotes a charging coil, and 8 denotes a preliminary ionization pin pair including a pair of upper and lower pins provided on both sides of the first and second main electrodes 1 and 2.

Next, the operation of the excitation circuit will be described. First, a high voltage is applied to the power supply terminal 1 and the charging coil 7
To charge the storage capacitor 4. When the switch 6 is turned on, a voltage equal to the charging voltage of the storage capacitor 4 is applied between the charging inductance 7 and the preliminary ionization pin pair 8. Since the charging voltage of the storage capacitor 4 is sufficiently higher than the discharge breakdown voltage between the pre-ionization pins, an arc discharge occurs between the pre-ionization pin pairs 8. The gas in the main discharge space is photo-ionized by the ultraviolet light generated from this arc discharge, and seed electrons are uniformly supplied into the space (preliminary ionization). In addition, conduction between the preliminary ionization pin pairs 8 is started by the start of the arc discharge, and a closed circuit including the storage capacitor 4, the peaking capacitor 5, and the switch 6 is formed. Since the inductance of this closed circuit is set very small compared to the inductance of the charging coil 7,
The electric charge stored in the storage capacitor 4 mainly moves to the peaking capacitor 5, and the charging voltage of the peaking capacitor 5 increases rapidly. The charging voltage of the peaking capacitor 5 is equal to the voltage applied between the first main electrode 1 and the second main electrode 2, and when this voltage reaches the breakdown voltage between the main electrodes 1 and 2, Main discharge starts between the main electrodes 1 and 2 based on the seed electrons. At the start of the main discharge, the electric charge stored in the peaking capacitor 5 rapidly flows into the discharge field, and the laser gas between the main electrodes is excited.

The conventional example shown in FIG. 8 is a so-called automatic preionization system in which a preionization unit is incorporated in a part of the excitation circuit, and the preionization and the main discharge are constant in conjunction with the operation of the excitation circuit. that has become a mechanism which is carried out at the timing. The automatic preionization method is widely used because the circuit configuration is simple and the like, and is particularly common in laser devices aimed at industrial applications.

FIG. 9 shows, for example, a document (K. MIDORIK).
AWA et al, "X-RayPreioniza
Tion of Rare-GAS-Halide L
asers ”, IEEE J. Quantum Ele
ctoron. QE-20, NO. 3, P198, 19
FIG. 84 is an excitation circuit configuration diagram of the conventional discharge excitation pulse laser device shown in 84). In the figure, the same reference numerals as those in FIG.
It is the same part or a corresponding part. In the conventional example shown in FIG. 8, preliminary ionization is performed using ultraviolet light generated from arc discharge. In this conventional example, preliminary ionization of the discharge space is performed using X-rays. In the figure, reference numeral 9 denotes a pulse shaping line that is configured to match the impedance with the main discharge in order to store energy to be input to the discharge field and efficiently input the stored energy to the main discharge field. Reference numeral 10 denotes a pulse charger for charging the pulse shaping line 9, and reference numeral 11 denotes a rail gap that performs switching between the pulse shaping line 9 and the discharge unit. 12 is an X-ray generator, 13 is a Marx generator for applying a high voltage to the X-ray generator 12, 14 is a trigger generator for generating a signal serving as a reference for starting a circuit operation, and 15 is a delay circuit. This example is different from the automatic preionization method described above in that the timing of preionization and main discharge is set by the trigger generator 14 and the delay circuit 15.

Next, the operation of the excitation circuit will be described. First, two reference signals are simultaneously generated from the trigger generator 14. Based on one signal, a high voltage is applied to the X-ray generator 12 via the Marx generator 13 to generate X-rays. The laser gas between the main electrodes 1 and 2 is pre-ionized by the X-rays. The other signal is sent to the delay circuit 15, and the pulse shaping line 9 is charged via the pulse charger 10 with a time delay corresponding to the setting of the delay circuit 15. The charging voltage of the pulse shaping circuit 9 is the rail gap 1
When the dielectric breakdown voltage between the rod electrodes within 1 is exceeded, a plurality of arc discharges are generated between the same electrodes, thereby performing switching. As the switching of the rail gap 11 starts, the voltage applied to the first main electrode 1 also increases rapidly. When the voltage applied to the first main electrode 1 exceeds the breakdown voltage between the main electrodes 1 and 2, the main discharge starts. At this time, the energy stored in the pulse shaping line 9 is supplied to the main discharge field, and the laser gas is excited.

FIG. 10 shows a reference (M. Steyer and
H. Vogas, "Parametric Stud
y of X-Ray PreionizedHigh
-Pressure Rare Gas Halid
e Lasers ", Appl. Phys. B42, P
155-160, 1987) is a graph showing the preionization timing dependency of the laser output. In this graph, the horizontal axis represents the preionization timing, and the vertical axis represents the laser output. The preionization timing is defined as the time from the start time of the X-ray pulse used for preionization to the peak of the laser pulse. It can be seen that the output greatly depends on the preionization timing, and there is an optimum value for the preionization timing. FIG. 11 shows the measured values of the pre-ionization timing with respect to the charging voltage of the May capacitor in the excitation circuit, and FIG. 12 plots the results with respect to the krypton concentration in the laser gas composition. From the figure, it can be seen that the optimum value of the preionization timing also changes depending on the gas composition of the laser gas and the operating conditions of the laser such as the method of applying a voltage between the main electrodes 1 and 2.

In the automatic preionization system shown in FIG. 8, the timing of preionization is automatically determined by circuit constants such as inductance determined by the capacity and structure of the capacitor. As described above, the optimal preionization timing changes depending on the operating conditions.However, in this method, changing the preionization timing involves changing the circuit constant of the excitation circuit. It was difficult to maintain the timing of the preionization at the optimal position. On the other hand, in the conventional example shown in FIG. 9, the circuit for performing the main discharge and the circuit for performing the preionization are independent from each other, and the timing of the main discharge and the preionization is set using the delay circuit 15. Preliminary ionization timing as set forth in the application is not set, and the dependence of laser output on preliminary ionization timing is measured in advance under each laser operating condition, and the delay time is set so that the preionization timing at which the highest output is obtained is obtained. It is usual to set and use.

In view of the industrial application of the discharge excitation pulse laser, it is essential that continuous operation is possible. In the case of continuous operation, the operating condition of the laser changes over time due to deterioration of the laser gas and the like, and accordingly, the optimum value of the preionization timing also changes. On the other hand, conventionally, even when the timing of the preionization is fixed or the adjustment is performed, the reference is only the laser output. For this reason, when trying to adjust the timing of preliminary ionization to an optimal position at all times during continuous operation, the laser output has to be constantly monitored. However, in order to monitor the laser output, a part of the laser light has to be extracted using an optical element such as a beam splitter, which causes a reduction in efficiency. Further, not only optical elements but also special instruments such as a laser power meter are used, which requires not only complicated work but also a large amount of cost.

[0010]

The conventional discharge excitation pulse laser apparatus is constructed as described above. When an automatic preionization system as shown in FIG. It is impossible to change the timing sequentially. In a system having a preliminary ionization circuit independent of the excitation circuit as shown in FIG. 9, it is possible to adjust the timing of the preliminary ionization according to the operating conditions. Since there was no method other than measuring the laser output, it was necessary to constantly monitor the laser output during the laser operation in order to always maintain the optimal preionization timing with respect to the temporal change of the operating conditions. However, in order to monitor the laser output, a part of the laser light must be extracted, which causes a problem that the efficiency is reduced. In addition, in order to monitor the laser output, it is necessary to use an optical element such as a beam splitter for extracting a laser beam or a laser power meter, which requires not only complicated work but also high costs. There was a problem.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides a clear reference indicating the optimal preionization timing in place of the laser output. It is an object of the present invention to provide a discharge excitation pulse laser device which can be adjusted to a proper position and can obtain high efficiency oscillation.

[0012]

According to a first aspect of the present invention, there is provided a discharge excitation pulse laser apparatus which includes a pre-ionization timing point for minimizing an absolute value of a firing voltage between main electrodes in a duration of the pre-ionization. The preionization timing is set in the range.

Further, a pre-ionization timing point for minimizing a time required for main discharge to start between the first and second main electrodes after a voltage is applied between the main electrodes is defined as a duration of the pre-ionization. The preliminary ionization timing is set in a range that is included therein.

Further, an adjusting means for adjusting the preionization timing to an optimum value by monitoring a discharge starting voltage between the main electrodes is provided.

Further, adjusting means for adjusting the pre-ionization timing to an optimum value by monitoring the time from when a voltage is applied between the main electrodes to when the main discharge starts between the first and second main electrodes. Is provided.

[0016]

According to the discharge excitation pulse laser apparatus of the present invention, the preionization timing can be easily set to an optimum position by the above means without measuring the laser output unlike the prior art, and the laser oscillation with high efficiency can be achieved. Can be obtained.

Since the operation of the excitation circuit is determined by the circuit constants, the time required from the application of a voltage between the main electrodes to the start of the main discharge between the main electrodes is determined by the time between the start of the discharge between the main electrodes. The shorter the absolute value of the voltage, the shorter.
Therefore, after a voltage is applied between the main electrodes, the first and second
The pre-ionization timing point that minimizes the time required for the main discharge to start between the main electrodes is equal to the pre-ionization timing point that minimizes the absolute value of the firing voltage. The above effect can be obtained even if the pre-ionization timing is set in a range that includes the pre-ionization timing point that minimizes the time required until the start, within the duration of the pre-ionization.

[0018]

Embodiment 1 FIG. 1 shows a setting range of a preionization timing of a discharge excitation pulse laser device according to an embodiment of the present invention, and a relationship between the setting range and a firing voltage between main electrodes. is there. Note that the discharge excitation pulse laser device according to this embodiment is
A corona preionization method is used in which the laser gas is preionized by ultraviolet light generated from corona discharge. In the figure, the horizontal axis represents the preionization timing. Here, the preionization timing was defined as the time from the start of voltage application between the main electrodes to the peak of the pulse current flowing through the preionization part.
In this embodiment, setting the preionization timing within the range of T ₁ shown in the figure T _2. In the figure, 16 is a curve showing the dependence of the discharge start voltage between the main electrodes on the pre-ionization timing, and 17 is a pulse current waveform flowing through the pre-ionization part at the pre-ionization timing T _{0 at} which the discharge start voltage between the main electrodes is minimized. , 18 the pulse waveform of the current flowing through the pre-ionization unit in preionization timing T _1, 19 is a pulse waveform of the current flowing through the pre-ionization unit in preionization timing T _2. It is safe to assume that the preionization is being performed while the current is flowing through the preionization part, and the pulse width of the current waveform indicated by τ in the figure is the duration of the preionization.
T ₁ is the pre-ionized timing the end point of the pulse current is equal to T _0, T ₂ is the pre-ionized timing the start point of the pulse current is equal to T _0. When the range of the preionization timing is set as shown in the present embodiment, the preionization timing for minimizing the firing voltage between the main electrodes during the duration of the preionization is included.

FIG. 2 shows the results of a measurement of the laser output of the discharge excitation pulse laser device equivalent to this embodiment, the correlation between the discharge starting voltage between the main electrodes, and the preionization timing. In the figure, the horizontal axis represents the preionization timing, and the vertical axis represents the laser output and the discharge starting voltage. The preionization timing at which the maximum output is obtained almost coincides with the preionization timing at which the discharge starting voltage becomes minimum. FIG. 3 shows a waveform of a pulse current flowing to the preliminary ionization unit at the time of measuring the correlation. The peak value of the current is about 400
A, about 40 ns from the rise to the peak of the current, about 50 ns from the peak to the stop, the pulse width of the current,
That is, the duration of the preionization is about 90 ns. According to the setting range of the pre-ionization timing shown in FIG. 1, the pre-ionization timing may be set within a range from 50 ns before to 40 ns behind with reference to the pre-ionization timing that minimizes the discharge starting voltage between the main electrodes. It is clear from FIG. 2 that within the setting range of the preliminary ionization timing, an output of about 80% or more as compared with the maximum value is obtained, and the laser can be oscillated efficiently.

Embodiment 2 FIG. 4 shows the discharge starting voltage between the main electrodes and the time between the start of the application of the voltage between the main electrodes and the time between the main electrodes of the corona pre-ionization type discharge excitation pulse laser device as in the above embodiment. FIG. 9 shows a result of an actual measurement of a correlation between a time required until discharge starts and a preionization timing. In this embodiment, the preionization timing is defined in the same manner as in the previous embodiment. As described above, the operation of the excitation circuit is determined by the circuit constant. Therefore, the time required from the application of the voltage between the main electrodes to the start of the main discharge becomes shorter as the absolute value of the discharge start voltage becomes smaller. FIG. 4 shows the time required from the start of voltage application between the main electrodes as a reference point to the start of discharge between the main electrodes from this reference point with respect to the preionization timing. The pre-ionization timing for minimizing the discharge start voltage and the pre-ionization timing for minimizing the time required until the start of discharge coincide with each other. The same effect as in the above embodiment can be obtained by using the time required for the discharge between the main electrodes to start as the reference indicating the optimal pre-ionization timing, similarly to the discharge starting voltage in the above embodiment.

Embodiment 3 In the above embodiment, the starting point of the time before the start of the main discharge was the time when the application of the voltage between the main electrodes was started. The same effect as in the above embodiment can be obtained even when the operation of another excitation circuit is started.

Further, in the above embodiment, the corona preionization system has been described, but the same applies to other preionization systems such as a UV spark preionization system utilizing arc discharge.

Further, in the above embodiment, the preliminary ionization timing point for minimizing the absolute value of the discharge starting voltage between the main electrodes is
The pre-ionization timing was set in a range that included the duration of the pre-ionization, but if the pre-ionization timing was set closer to the pre-ionization timing point that minimizes the absolute value of the firing voltage, It is clear that more efficient laser oscillation can be obtained.

Embodiment 4 FIG. 5 is a circuit diagram showing an embodiment of the present invention. In the drawing, those having the same reference numerals as those in FIG. 8 or FIG. 9 are the same or corresponding parts. In the figure, reference numeral 20 denotes a main discharge circuit for applying a high voltage between the main electrodes 1 and 2 to form a main discharge. Reference numeral 21 denotes a preliminary ionization source, and reference numeral 22 denotes a preliminary ionization source driving circuit for driving the preliminary ionization source 21. 23 is a voltage measuring device for monitoring the discharge starting voltage between the main electrodes 1 and 2; 24 is a device for judging the timing of preliminary ionization for the next circuit operation from the measured value of the discharge starting voltage, and instructing the delay circuit 15 to change the delay time. Time discriminator that sends a signal for the delay time.

Next, the operation of this embodiment will be described.
As in the conventional example shown in FIG. 9, first, the trigger generator 14 simultaneously generates two reference signals. Voltage application between the main electrodes 1 and 2 via the main discharge circuit 20 starts based on one signal. The other signal is sent to the delay circuit 15, and the laser gas between the main electrodes 1 and 2 is preliminarily ionized by the preionization source 21 via the preionization source driving circuit 22 with a time delay corresponding to the setting of the delay circuit 15. Is done. When the voltage applied by the main electrode circuit 20 exceeds the breakdown voltage between the main electrodes 1 and 2, the main discharge starts. The discharge start voltage is always measured by the voltage measuring device 23, and the delay time discriminator determines the delay time for the next circuit operation by comparing the two immediately preceding discharge start voltage measurement values. Is sent to the delay circuit 15.

FIG. 6 is a flowchart showing the processing performed by the delay time discriminator 24. If the pre-ionization timing is adjusted according to this flowchart, the range of the delay time step set by the delay time discriminator 24 with respect to the pre-ionization timing that minimizes the discharge start voltage between the main electrodes, regardless of the laser operating conditions. Within this, the preionization timing can be maintained. Further, according to this embodiment, it is not necessary to take out and monitor a part of the laser output,
The pre-ionization timing can be maintained at the optimum value without lowering the efficiency. Also, the method itself is simple because only the voltage needs to be measured.

Embodiment 5 FIG. 7 is a circuit diagram showing a discharge excitation pulse laser apparatus according to an embodiment of the present invention. In the figure, reference numeral 25 denotes a current detector installed in a current introducing portion of the main electrode 1, reference numeral 26 denotes a first pulse generator for generating a pulse triggered by a signal from the voltage measuring device 23, and reference numeral 27 denotes a current detector 25. It is a second pulse generator that generates a pulse using a signal as a trigger. Reference numeral 28 denotes a time-to-peak converter for converting the interval between two pulses into a pulse height.

The time required before the start of discharge after the voltage is applied between the main electrodes is one of the criteria indicating the optimal pre-ionization timing similarly to the discharge start voltage, and the time required until the start of discharge is minimized. As described above, the preliminary ionization timing is the optimal preliminary ionization timing. In this embodiment, the start of voltage application between the main electrodes is sensed by the voltage measuring device 23, a pulse is generated by the first pulse generator 26 using this signal as a trigger, and the start of discharge is sensed by the current detector 25. Then, a pulse is generated by the second pulse generator 27 using this signal as a trigger. When a pulse generated from the first pulse generator 26 is used as a start signal and a pulse generated from the second pulse generator 27 is used as a stop signal and input to the time-to-peak converter 28, the time interval between the two pulses becomes Converted as wave height. This pulse height represents the time required from the time when the voltage is applied between the main electrodes to the start of the discharge, and the same effect can be obtained by treating the same as the measured value of the discharge start voltage in the previous embodiment.

Embodiment 6 The flow chart shown in FIG. 6 controls the preionization timing for each pulse. By comparing the average of the firing voltages with the appropriate number of pulses as one set, a comparison is made. Even if the preionization timing is adjusted, not only the same effect as in the fourth embodiment can be obtained, but also a variation in the discharge starting voltage due to each pulse is canceled out, so that a stable circuit operation can be obtained.

Embodiment 7 The method of controlling the timing of preliminary ionization by taking an average with an appropriate number of pulses as one set is also effective for a method based on the time until the start of discharge. Not even.

[0031]

As described above, according to the present invention, the pre-ionization timing of the discharge excitation pulse laser device is determined by the pre-ionization timing point at which the absolute value of the discharge starting voltage between the main electrodes becomes minimum, and the duration of the pre-ionization. Since the pre-ionization timing is set based on the criterion of the included range, the preionization timing can be set to an optimum value without lowering the efficiency, and there is an effect that highly efficient laser oscillation can be obtained. Further, according to the present invention, since the optimal preionization timing can be obtained only by measuring the discharge starting voltage, it is not necessary to use the laser power meter or the optical element used for the laser output measurement, and the preionization can be easily performed. Not only can the timing be set, but also the cost required for setting can be reduced.

Further, a pre-ionization timing point that minimizes the time required for the discharge to start between the main electrodes after a voltage is applied between the main electrodes is defined as a range included in the duration of the pre-ionization. The same effect as described above can be obtained by the reference of the ionization timing.

Further, by providing an adjusting means for adjusting the preionization timing to an optimum value by monitoring the discharge starting voltage, the preionization timing can be easily adjusted to the optimum value without lowering the efficiency even during continuous operation. Since it can be maintained, there is an effect that stable and highly efficient laser oscillation can always be obtained.

Further, an adjusting means for adjusting the pre-ionization timing to an optimum value by monitoring a time required until a discharge is started between the main electrodes after a voltage is applied between the main electrodes may be provided. The same effect as described above can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a setting range of preliminary ionization of a discharge excitation pulse laser device according to a first embodiment of the present invention, and a relationship between the setting range and a firing voltage between main electrodes.

FIG. 2 is a graph showing a laser output of a discharge excitation pulse laser device used in Example 1 of the present invention, and a measurement result of a correlation between a discharge starting voltage between main electrodes and a preionization timing.

FIG. 3 is a pulse current waveform flowing to a preliminary ionization part when measuring the correlation shown in FIG. 2;

FIG. 4 shows the correlation between the discharge starting voltage between the main electrodes and the time required from the start of voltage application to the main electrodes to the start of discharge in the discharge excitation pulse laser device according to the second embodiment of the present invention, and the preionization timing. 5 is a graph showing the results of actual measurements for.

FIG. 5 is a circuit configuration diagram of a discharge excitation pulse laser device according to Embodiment 3 of the present invention.

FIG. 6 is a flowchart illustrating a method of adjusting preionization timing according to a third embodiment of the present invention.

FIG. 7 is a circuit configuration diagram of a discharge excitation pulse laser device according to a fourth embodiment of the present invention.

FIG. 8 is a circuit configuration diagram of a conventional discharge excitation pulse laser device.

FIG. 9 is a circuit configuration diagram of a conventional discharge excitation pulse laser device.

FIG. 10 is a graph showing a correlation between preionization timing and laser output in a discharge excitation pulse laser device.

FIG. 11 is a graph showing a measurement result of a correlation between a main capacitor charging voltage in an excitation circuit and an optimal value of a preliminary ionization voltage in a discharge excitation pulse laser device.

FIG. 12 is a graph showing an actual measurement result of a correlation between a krypton concentration in a laser gas composition and an optimum value of a preliminary ionization voltage in a discharge excitation pulse laser device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 1st main electrode 2 2nd main electrode 8 Preionization pin pair 12 X-ray generator 13 Marx generator 14 Trigger generator 15 Delay circuit 16 Curve showing preionization timing dependency of discharge start voltage between main electrodes 17 A pulse current waveform flowing through the preliminary ionization section at the preliminary ionization timing T ₀ that minimizes the discharge start voltage between the main electrodes 18 A pulse current waveform flowing through the preliminary ionization section at the preliminary ionization timing T ₁ 19 A preliminary ionization section at the preliminary ionization timing T ₂ 20 Main discharge circuit 21 Pre-ionization source 22 Pre-ionization source drive circuit 23 Voltage measuring device 24 Delay time discriminator 25 Current detector 26 First pulse generator 27 Second pulse generator 28 Time-wave height converter

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01S 3/097-3/0977

Claims (4)

(57) [Claims] A first and a second main electrode provided to face each other to generate a main discharge in a laser gas; an excitation circuit connected to the first and the second main electrodes; 2
Bei In the discharge exciting pulse laser device, means for detecting a discharge start voltage between the main electrodes with a laser gas between the main electrodes and the preionization source for pre-ionization before the main discharge of the
In addition , the discharge excitation pulse laser device is characterized in that the pre-ionization timing is set within a range such that the pre-ionization timing point that minimizes the absolute value of the discharge start voltage is included in the duration of the pre-ionization. A first and a second main electrode provided to face each other to cause a main discharge in the laser gas; an excitation circuit connected to the first and the second main electrodes; 2
And a pre-ionization source for pre-ionizing the laser gas between the main electrodes of the discharge excitation pulse laser device, after a voltage is applied between the main electrodes, between the first and second main electrodes. A discharge excitation pulse laser device, wherein a pre-ionization timing is set within a range in which a pre-ionization timing point for minimizing a time required to start a main discharge is included in a duration of the pre-ionization. 3. The discharge excitation pulse laser device according to claim 1, further comprising adjusting means for adjusting a timing of the preionization to an optimum value by monitoring a discharge starting voltage between the main electrodes. Discharge pump laser device. 4. A discharge excitation pulsed laser apparatus of claim 2, wherein, after the voltage has been marked pressurized between the main electrodes, monitoring the time required for the main discharge starts between the first and second main electrodes A discharge excitation pulse laser device characterized in that an adjustment means for adjusting the timing of the preionization to an optimum value is provided.