JPH05102578A - Discharge excited pulse laser device - Google Patents

Abstract

PURPOSE:To set up the criterion representing the optical auxiliary ionization timing substituting for laser output for making the highly efficient oscillation step feasible by a method wherein the auxiliary ionization timing is set up within the range wherein the auxiliary ionization timing point is contained in the duration of the auxiliary ionization step. CONSTITUTION:The title discharge excited pulse laser device adopts the corona auxiliary ionization system for auxiliary ionizing a laser gas by the ultraviolet rays emitted from corona discharge. The auxiliary ionization step can be assumed to be performed while a current is running in the auxiliary ionizing part so that the pulse width of a current wave form may represent the duration of the auxiliary ionization. At this time, T1 represents the auxiliary ionization timing when the terminal point of a pulse current is equalized to T0 while T2 represents the auxiliary ionization timing when the starting point is equalized to T0. At this time, the auxiliary timing minimizing the discharge starting voltage (c) is contained in the duration of the auxiliary ionization. Through these procedures, the optimum auxiliary timing can easily be set up simply by measuring the discharge starting voltage (c).

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art In order to efficiently excite a laser by discharge, it is essential to generate a uniform main discharge. For this reason, pre-ionization is usually performed in advance in the discharge field before the main discharge is generated to generate electrons that are the seeds of the discharge. FIG. 8 is a pump circuit configuration diagram of a conventional discharge pump pulse laser device, which is cited from, for example, a document ("Development of excimer laser and its applied technology / example", directed by Shuntaro Watanabe, Applied Technology Publishing, p17). Generally, the circuit shown in the figure is called a capacitance transfer type circuit. In the figure, 1 is a first main electrode and 2 is a second main electrode. 3 is a power supply terminal provided for supplying a high voltage to the excitation circuit, 4 is a storage capacitor, and 5 is a peaking capacitor. Reference numeral 6 is a switch, 7 is a charging coil, and 8 is a preionization pin pair composed of 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 this excitation circuit will be described. First, a high voltage is applied to the power supply terminal 1, and the charging coil 7
Through which the storage capacitor 4 is charged. 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 preionization pin pair 8. Since the charging voltage of the storage capacitor 4 is sufficiently higher than the discharge breakdown voltage between the preionization pins, arc discharge occurs between the preionization pin pair 8. Ultraviolet light generated from this arc discharge photoionizes the gas in the main discharge space and uniformly supplies seed electrons into the space (pre-ionization). When the arc discharge starts, the preionization pin pair 8 is electrically connected to form a closed circuit including the storage capacitor 4, the peaking capacitor 5, and the switch 6. Since the inductance of this closed circuit is set to be much smaller than the inductance of the charging coil 7,
The charges stored in the storage capacitor 4 mainly move to the peaking capacitor 5, and the charging voltage of the peaking capacitor 5 rapidly increases. 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 dielectric breakdown voltage between the main electrodes 1 and 2, Main discharge starts between the main electrodes 1 and 2 based on the seed electrons. With the start of the main discharge, the charges accumulated in the peaking capacitor 5 steeply flow into the discharge field, and the laser gas between the main electrodes is excited.

The conventional example shown in FIG. 8 is called an automatic preionization system in which a preionization unit is incorporated in a part of an excitation circuit, and the preionization and main discharge are constant in conjunction with the operation of the excitation circuit. It is a mechanism that is performed at the timing. This method is usually called an automatic preionization method. The automatic preionization method is widely used because of its simple circuit configuration, and it is the most popular method especially for laser devices for industrial application.

FIG. 9 shows, for example, a document (K. MIDIREK).
AWA et al, "X-Ray Preioniza
region of Rare-GAS-Halide L
asers ", IEEE J. Quantum Ele
ctoron. QE-20, NO. 3, P198, 19
FIG. 84 is a pump circuit configuration diagram of the conventional discharge pump pulse laser device shown in FIG. In the figure, the same reference numerals as those in FIG.
The same part or a corresponding part. In the conventional example shown in FIG. 8, the pre-ionization is performed by using the ultraviolet light generated from the arc discharge, but in the conventional example, the pre-ionization of the discharge space is performed by using the X-ray. In the figure, reference numeral 9 is a pulse shaping line that is designed to have impedance matching with the main discharge in order to store the energy to be input into the discharge field and to efficiently input the stored energy into the main discharge field. Reference numeral 10 is a pulse charger for charging the pulse shaping line 9, and 11 is a rail gap for switching between the pulse shaping line 9 and the discharging unit. Reference numeral 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 the circuit operation, and 15 is a delay circuit. Unlike the automatic preionization method described above, this example has a configuration in which the timings of preionization and main discharge are set by the trigger generator 14 and the delay circuit 15.

Next, the operation of this excitation circuit will be described. First, the trigger generator 14 simultaneously generates two reference signals. A high voltage is applied to the X-ray generator 12 via the Marx generator 13 based on one signal, and X-rays are generated. The X-ray pre-ionizes the laser gas between the main electrodes 1 and 2. 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 charge voltage of the pulse shaping circuit 9 is the rail gap 1
When the breakdown voltage between the rod electrodes in 1 is exceeded, a plurality of arc discharges occur between the electrodes, which causes switching. When the switching of the rail gap 11 is started, the voltage applied to the first main electrode 1 also rapidly increases. When the applied voltage to the first main electrode 1 exceeds the breakdown voltage between the main electrodes 1 and 2, main discharge starts. At this time, the energy stored in the pulse shaping line 9 is input to the main discharge field to excite the laser gas.

FIG. 10 shows a document (M. Steyer and
H. Vogas, "Parametric Study
y of X-Ray Preionized High
-Pressure Rare Gas Halide
e Lasers ", Appl. Phys. B42, P.
155-160, 1987) is a graph showing the preionization timing dependence of the laser output shown in FIG. 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 largely depends on the preionization timing, and there is an optimum value for the preionization timing. FIG. 11 is a graph in which the optimum values of the preionization timings are measured and plotted with respect to the charging voltage of the May capacitor in the excitation circuit and FIG. 12 with respect to the krypton concentration in the laser gas composition. From the figure, it is understood that the optimum value of the preionization timing varies depending on the gas composition of the laser gas, the operating condition of the laser such as the method of applying the 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 the circuit constant such as the inductance determined by the capacitance and structure of the capacitor. As described above, the optimum 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, so it is always irrespective of the laser operating conditions. It was difficult to maintain the timing of preionization at the optimum position. On the other hand, in the conventional example shown in FIG. 9, the main discharge circuit and the preliminary ionization circuit are independent of each other, and the delay circuit 15 is used to set the main discharge timing and the preliminary ionization timing. The preionization timing is not set as in the application, and the preionization timing dependency of the laser output is measured beforehand under each laser operating condition, and the delay time is set so that the highest output is obtained. Is usually set and used.

Considering the industrial application of the discharge excitation pulsed laser, it is essential that continuous operation is possible. When performing continuous operation, the operating conditions of the laser change with time due to reasons such as deterioration of the laser gas, and the optimum value of the preionization timing also changes accordingly. On the other hand, conventionally, the timing of preionization is fixed, or even if adjustment is performed, only the laser output is the reference. Therefore, in order to adjust the timing of preionization to the optimum position at all times during continuous operation, it was necessary to constantly monitor the laser output. However, in order to monitor the laser output, a part of the laser light must be taken out by using an optical element such as a beam splitter, which causes a decrease in efficiency. Further, not only an optical element but also a special instrument such as a laser output meter is used, so that not only complicated labor is required, but also much cost is required.

[0010]

The conventional discharge-pumped pulse laser device is constructed as described above, and when the automatic preionization system as shown in FIG. 8 is adopted, the preionization is performed according to the operating conditions of the laser. It is impossible to change the timing sequentially. Further, in the method having the preionization circuit independent of the excitation circuit as shown in FIG. 9, it is possible to adjust the preionization timing according to the operating conditions, but in order to determine the optimum preionization timing. Since there was no other method than measuring the laser output, it was necessary to constantly monitor the laser output during laser operation in order to always maintain the optimum preionization timing with respect to changes over time in operating conditions. However, in order to monitor the laser output, it is necessary to take out a part of the laser beam, which causes a problem of efficiency reduction. Further, in order to monitor the laser output, it is necessary to use an optical element such as a beam splitter for extracting the laser light and a laser output meter, which not only requires complicated labor but also costs a lot. There was a problem.

The present invention has been made in order to solve the above problems, and provides a clear reference for the optimum preionization timing that changes to the laser output, and the preionization timing can be easily optimized by this reference. It is an object of the present invention to provide a discharge-pumped pulse laser device that can be adjusted to various positions and can obtain high-efficiency oscillation.

[0012]

The discharge excitation pulse laser device according to the present invention includes a preionization timing point that minimizes the absolute value of the discharge start voltage between the main electrodes during the duration of the preionization. Pre-ionization timing is set in the range.

Further, the preionization timing point that minimizes the time required to start the main discharge between the first and second main electrodes after the voltage is applied between the main electrodes is defined as the duration of the preionization. The preliminary ionization timing is set within the range included in the inside.

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

Furthermore, by adjusting the time until the main discharge starts between the first and second main electrodes after the voltage is applied between the main electrodes, the adjusting means for adjusting the preionization timing to the optimum value. Is provided.

[0016]

The discharge excitation pulse laser device according to the present invention can easily set the preionization timing to the optimum position by the above means without measuring the laser output as in the conventional case, and highly efficient laser oscillation is possible. Can be obtained.

Further, since the operation of the excitation circuit is determined by the circuit constant, the time required from the application of the voltage between the main electrodes to the start of the main discharge between the main electrodes is the start of the discharge between the main electrodes. It becomes shorter as the absolute value of the voltage becomes smaller.
Therefore, after the voltage is applied between the main electrodes, the first and second electrodes
The preionization timing point that minimizes the time required for the main discharge to start between the main electrodes of is equal to the preionization timing point that minimizes the absolute value of the discharge start voltage. Even if the preionization timing is set in a range such that the preionization timing point that minimizes the time required for the start is included in the duration of the preionization, the above effect can be obtained.

[0018]

EXAMPLE 1 FIG. 1 shows a setting range of a preionization timing of a discharge excitation pulse laser device according to an example of the present invention and a relationship between the setting range and a discharge starting voltage between main electrodes. is there. The discharge excitation pulsed laser device according to this embodiment is
The corona pre-ionization method is used to pre-ionize the laser gas with the ultraviolet light generated from the corona discharge. In the figure, the horizontal axis represents the preionization timing. Here, the preionization timing is 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, the preionization timing is set within the range of T ₁ to T ₂ shown in the figure. In the figure, 16 is a curve showing the dependence of the discharge start voltage between the main electrodes on the preionization timing, and 17 is the pulse current waveform flowing through the preionization part at the preionization timing T ₀ that minimizes the discharge start voltage between the main electrodes. , 18 is a pulse current waveform flowing through the preliminary ionization portion at the preliminary ionization timing T ₁ , and 19 is a pulse current waveform flowing through the preliminary ionization portion at the preliminary ionization timing T ₂ . It can be considered that pre-ionization is performed while the current is flowing through the pre-ionization unit. In the figure, the pulse width of the current waveform indicated by τ is the duration of pre-ionization.
T ₁ is the preionization timing at which the end point of the pulse current is equal to T ₀ , and T ₂ is the preionization timing at which the start point of the pulse current is equal to T ₀ . If the range of the preionization timing is set as shown in this embodiment, the preionization timing that minimizes the discharge start voltage between the main electrodes during the duration of the preionization is included.

FIG. 2 shows the result of actual measurement of the laser output of a discharge excitation pulse laser device equivalent to that of this embodiment, the correlation between the discharge start voltage between the main electrodes and the preionization timing. In this figure, the horizontal axis represents the preionization timing, the vertical axis represents the laser output, and the discharge start voltage. The preliminary ionization timing at which the maximum output is obtained and the preliminary ionization timing at which the discharge start voltage is minimized are almost the same. FIG. 3 is a waveform of the pulse current flowing to the preionization part at the time of measuring the correlation. Peak 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 preionization is about 90 ns. According to the setting range of the preionization timing shown in FIG. 1, the preionization timing that minimizes the discharge start voltage between the main electrodes may be set within the range from the front 50 ns to the rear 40 ns. It is clear from FIG. 2 that an output of about 80% or more is obtained within the set range of the above-mentioned preionization timing, and the laser can be efficiently oscillated.

Embodiment 2 FIG. 4 shows the discharge start voltage between the main electrodes of the corona preionization type discharge excitation pulse laser device as well as the above-mentioned embodiment and the time between the main electrodes from the time when the voltage is applied between the main electrodes. It shows the result of actual measurement of the correlation between the time required until the start of discharge and the preionization timing. Also in this embodiment, the preionization timing is defined as in the previous embodiment. As described above, the operation of the excitation circuit is determined by the circuit constant. Therefore, after the voltage is applied between the main electrodes, the time required to start the main discharge becomes shorter as the absolute value of the discharge start voltage becomes smaller. FIG. 4 shows the time required for starting the discharge between the main electrodes from the reference point at the time when the voltage application between the main electrodes is started as a reference point. Moreover, the preionization timing that minimizes the discharge start voltage and the preionization timing that minimizes the time required to start the discharge match. Even when the time required for the discharge to start between the main electrodes is used as a reference indicating the optimum preionization timing, as in the discharge start voltage of the above embodiment, the same effect as that of the above embodiment can be obtained.

Embodiment 3 In the above embodiment, the starting point of the time until the start of the main discharge is the time when the voltage application between the main electrodes is started, but the time when the applied voltage between the main electrodes reaches a certain value, etc. The same effect as that of the above-described embodiment can be obtained by using other excitation circuit operations as a starting point.

Further, in the above embodiment, the corona preionization method is shown, but the same applies to other preionization methods such as a UV spark preionization method using arc discharge.

In the above embodiment, the preionization timing point at which the absolute value of the discharge start voltage between the main electrodes is minimized,
Although the preionization timing was set to a range that included during the duration of preionization, if the preionization timing is set to a range closer to the preionization timing point that minimizes the absolute value of the discharge start voltage. It is clear that more efficient laser oscillation can be obtained.

Embodiment 4 FIG. 5 is a circuit configuration diagram showing an embodiment of the present invention. In the figure, the same symbols as those in FIG. 8 or FIG. 9 indicate the same or corresponding portions. In the figure, 20 is a main discharge circuit for applying a high voltage between the main electrodes 1 and 2 to form a main discharge. Reference numeral 21 is a preliminary ionization source, and 22 is a preliminary ionization source driving circuit for driving the preliminary ionization source 21. Reference numeral 23 is a voltage measuring device for monitoring the discharge start voltage between the main electrodes 1 and 2, 24 is the timing of preionization for the next circuit operation from the discharge start voltage measurement value, and the delay time is changed to the delay circuit 15. Is a delay time discriminator that sends a signal for

Next, the operation of this embodiment will be described.
Similar to 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 starts via the main discharge circuit 20 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 pre-ionized by the pre-ionization source 21 via the pre-ionization source driving circuit 22 with a time delay corresponding to the setting of the delay circuit 15. To be done. When the voltage applied by the main electrode circuit 20 exceeds the dielectric breakdown voltage between the main electrodes 1 and 2, main discharge starts. The discharge start voltage is constantly measured by the voltage measuring device 23, and the delay time discriminator compares the immediately preceding two discharge start voltage measured values to determine the delay time for the next circuit operation. Is sent to the delay circuit 15.

FIG. 6 is a flowchart showing the processing performed by the delay time discriminator 24. If the preliminary 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 preliminary ionization timing that minimizes the discharge start voltage between the main electrodes regardless of the laser operating conditions. The preionization timing can be maintained within. Further, according to this embodiment, it is not necessary to take out a part of the laser output and monitor it.
It is possible to maintain the preionization timing at the optimum value without reducing the efficiency. Moreover, the method itself is simple because it is only necessary to measure the voltage.

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

After the voltage is applied between the main electrodes, the time required until the start of discharge is one reference indicating the optimal preionization timing as with the discharge start voltage, and the time required before the start of discharge is minimized. As described above, the preionization timing becomes the optimum preionization timing. In the present embodiment, the voltage measuring device 23 senses the start of voltage application between the main electrodes, the signal is used as a trigger to generate a pulse in the first pulse generator 26, and the current detector 25 senses the start of discharge. Then, using this signal as a trigger, the second pulse generator 27 generates a pulse. When the pulse generated from the first pulse generator 26 is used as a start signal and the pulse generated from the second pulse generator 27 is used as a stop signal, and input to the time-to-wave height converter 28, the time interval between the two pulses is a pulse. Converted as wave height. This pulse wave height represents the time required from the start time of voltage application between the main electrodes to the start of discharge, and if treated in the same manner as the discharge start voltage measured value in the previous example, the same effect can be obtained.

Embodiment 6 In the flow chart shown in FIG. 6, the preionization timing is controlled for each pulse. By setting an appropriate number of pulses as one set and averaging the discharge start voltage, comparison is made. Even if the preionization timing is adjusted, not only the effect similar to that of the fourth embodiment is obtained, but also the variation of the discharge start voltage due to each pulse is canceled, so that the stable circuit operation is obtained.

Embodiment 7 It is said that the method of controlling the timing of preionization by averaging with an appropriate number of pulses as one set is also effective for the method based on the time until the start of discharge. There is no end.

[0031]

As described above, according to the present invention, the preionization timing of the discharge excitation pulsed laser device is set to the preionization timing point at which the absolute value of the discharge starting voltage between the main electrodes becomes the minimum. Since it is set according to the standard of the range included in the inside, it is possible to set the preionization timing to an optimum value without lowering the efficiency, and it is possible to obtain highly efficient laser oscillation. Further, according to the present invention, since the optimum preionization timing can be obtained only by measuring the discharge start voltage, it is not necessary to use the laser output meter or the optical element used for the laser output measurement, and the preionization can be easily performed. Not only the timing can be set, but also the cost required for the setting can be reduced.

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

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

Further, there may be provided an adjusting means for adjusting the preionization timing to the optimum value by monitoring the time required for the discharge to start between the main electrodes after the voltage is applied between the main electrodes. The same effect as described above can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a setting range of preionization of a discharge excitation pulsed laser device according to a first embodiment of the present invention and a relationship between the setting range and a discharge starting voltage between main electrodes.

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

FIG. 3 is a pulse current waveform flowing to the preionization unit when measuring the correlation shown in FIG.

FIG. 4 is a correlation between a discharge start voltage between main electrodes of a discharge excitation pulse laser device according to a second embodiment of the present invention, a time required from start of voltage application between main electrodes to start of discharge, and preionization timing. 3 is a graph showing the actual measurement results of the.

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

FIG. 6 is a flowchart showing a method for adjusting the preionization timing according to the 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 pulsed laser device.

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

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

FIG. 11 is a graph showing an actual measurement result regarding a correlation between a main capacitor charging voltage in an excitation circuit in a discharge excitation pulsed laser device and a preionization voltage optimum value.

FIG. 12 is a graph showing the actual measurement result of the correlation between the krypton concentration in the laser gas composition and the optimum value of the preionization voltage in the discharge excitation pulsed 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 the preionization timing dependence of the discharge start voltage between main electrodes 17 Pulse current waveform flowing through the preionization portion at the preionization timing T ₀ that minimizes the discharge start voltage between the main electrodes 18 Pulse current waveform flowing through the preionization portion at the preionization timing T ₁ 19 Preliminary ionization portion at the preionization timing T ₂ Current waveform 20 main discharge circuit 21 preionization source 22 preionization 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

Claims (4)

[Claims] 1. A first and a second main electrode, which are opposed to each other to cause a main discharge in a laser gas, and a first electrode.
A discharge excitation pulse laser device having an excitation circuit connected to the second main electrode and a preionization source for preionizing the laser gas between the first and second main electrodes prior to the main discharge. Discharge pre-ionization timing laser device is characterized in that the pre-ionization timing is set within a range that includes the pre-ionization timing point that minimizes the absolute value of the discharge start voltage of the above. 2. In the discharge excitation pulse laser device, a preionization timing that minimizes a time required for main discharge to start between the first and second main electrodes after a voltage is applied between the main electrodes. A discharge-excited pulsed laser device characterized in that the preionization timing is set within a range that includes points during the duration of preionization. 3. The discharge excitation pulse laser device according to claim 3, wherein the discharge start voltage between the main electrodes is monitored,
A discharge excitation pulsed laser device comprising an adjusting means for adjusting the timing of preionization to an optimum value. 4. In the discharge excitation pulse laser device, after the voltage is applied between the main electrodes, the time required for starting the main discharge between the first and second main electrodes is monitored, thereby providing a preliminary A discharge excitation pulsed laser device comprising an adjusting means for adjusting the ionization timing to an optimum value.