JPS6328085A - Discharge excitation pulse laser - Google Patents

Abstract

PURPOSE:To avoid an arc discharge after a main discharge is finished by a method wherein a short-circuit switch is provided in parallel with a discharge excitation part and the switch is short-circuited immediately before the main discharge is transferred to the arc discharge. CONSTITUTION:If a high voltage switch 6 is excited by a trigger control circuit 11 at time P, electric energy transfer starts and the time T1 for the electric energy transfer is approximately 100 nsec. By the electric energy transfer, a glow discharge starts at time Q between main electrodes 1a and 1b and a laser beam is emitted during a glow discharge time T2. At time R before the transfer to an arc discharge time T3, a short-circuit switch 10 is short-circuited. A time for determining the time R is predetermined to be about 100 nsec + several tens of nanoseconds in accordance with T1 + T2. Therefore, the performance is not degraded. Moreover, as the main discharge is forcibly discontinued at the time R immediately before the transfer from the glow discharge time T2 to the arc discharge time T3, the arc discharge is not generated between the main electrodes la and lb.

Description

[Detailed Description of the Invention] [Industrial Field of Application] This invention relates to a discharge-excited pulsed laser device such as an excimer laser that requires short-time discharge excitation, and in particular to an improvement in the performance and longevity of the discharge excitation part. This invention relates to a discharge-excited pulsed laser device that achieves this.

[Prior Art] In general, various circuits called capacitance transfer circuits or LC inversion circuits are used in discharge-excited pulsed laser devices to apply short pulse voltages between main electrodes.

Figure 4 shows, for example, “Laser Research (August 1984, Part 1)”.
FIG. 2 is a circuit diagram showing a conventional discharge-excited pulsed laser device such as an excimer laser using a capacitance transfer circuit, which is described on page 426 of "Volume 2)". In the figure, (1) is a discharge excitation part, and a pair of main electrodes (1a) and (1b) facing each other are shown.
) and a laser gas interposed between these main electrodes (la) and (1b). (2) is the discharge excitation part (1
) is an excitation capacitor connected in parallel to the main electrodes (1a) and (1b) to apply a short pulse voltage between the main electrodes (1a) and (1b) to generate glow emission Ti (main discharge).

(3) is connected in series to the excitation capacitor (2), and the laser gas in the discharge excitation part (1) is
It is a pre-ionization gap that generates ultraviolet light UV to separate i1t. This pre-ionization gap (3) for generating ultraviolet rays UY can be replaced with another pre-ionization mechanism such as an X-ray generator, so that the laser gas is pre-ionized by X-rays or the like instead of ultraviolet UV. Good too.

(4) is a charging inductance connected in parallel to a series circuit consisting of an excitation capacitor (2) and a preliminary ffl separation gap (3), and (5) is a charging inductance (4).
A pulse charging capacitor (6) is connected in parallel with the pulse charging capacitor (5), and (6) is a high voltage switch consisting of a Zyratron etc. connected in series with the pulse charging capacitor (5).
4) to (6) constitute a pulse charging circuit for charging the excitation capacitor (2) in a pulse manner.

The conventional discharge excitation pulsed laser device is configured as described above, in which electrical energy previously stored in the pulse charging capacitor (5) is transferred to the excitation capacitor (2) by activation of the high voltage switch (6). A main discharge is generated in the discharge excitation section (1).

First, a high voltage switch (
6) is activated and closed, the pulse charging capacitor (
The electrical energy stored in 5) is transferred to the high voltage switch (6
) to a parallel circuit consisting of a charging inductance (4), an excitation capacitor (2) and a preionization gap (3). And charging inductance (4)
, excitation capacitor (2) and preionization gap (3)
) according to the time constant of the pulse charging capacitor (5)
The electrical energy within is transferred to the excitation capacitor (2) via the preionization gap (3).

At this time, since the pre-ionization gaps (3) are connected by arc discharge, ultraviolet rays Uv are generated between the pre-ionization gaps (3). This ultraviolet ray 11/ is applied to the main electrode (
The laser gas between la) and (lb) is irradiated, and the main electrode (
Spatially uniform seed electrons are generated between 1a) and (1b).

From the pulse charging capacitor (5) to the excitation capacitor (
With the transfer of electrical energy to 2), the excitation capacitor (
2) increases the voltage between both terminals of the main electrodes (1a) and (1).
b) When the discharge starting voltage is reached between the main electrode (la),
(lb) Glow emission M (one emission and one emission occurs).

At this time, since uniform seed electrons are generated in the laser gas between the main electrodes (1a) and (1b), glow discharge is uniformly generated.

Due to this glow discharge, the discharge excitation part (1), the excitation capacitor (2) and the pre-ionization gap (3) constitute a main discharge circuit, and the electrical energy stored in the excitation capacitor (2) is transferred to the main electrode ( Excite the laser gas between 1a) and (tb). Therefore, a laser beam is emitted from the discharge excitation section (1), for example, in a direction perpendicular to the plane of the paper in FIG.

Generally, when the laser gas is under high pressure as in an excimer laser, it is difficult to maintain the glow discharge generated by uniform pre-ionization between the main electrodes (1a) and (lb) stably for a long time, so it is difficult to maintain the glow discharge. is number 10 to 10
It shifts to arc discharge in about 0 nanoseconds. However, since the time constant of the main discharge circuit is sufficiently small, the electrical energy stored in the excitation capacitor (2) is usually consumed before transition to arc discharge.

On the other hand, the pulse charging capacitor (5) stores enough electrical energy to charge the excitation capacitor (2), and due to the circuit configuration, it is difficult to input and consume all of this electrical energy during the main discharge. Very difficult. Therefore, the electrical energy that could not be transferred to the excitation capacitor (2) by the start of main discharge is transferred through a closed circuit consisting of the pulse charging capacitor (5), the high voltage switch (6), and the discharge excitation section (1). It is consumed as a current called aftercurrent.

However, since the time constant of this closed circuit is several times larger than the time constant of the main discharge circuit, the aftercurrent becomes an arc discharge that does not contribute to laser excitation at all, and the main electrode (la), (1
b) is likely to be consumed between.

[Problems to be Solved by the Invention] As described above, in the conventional discharge-excited pulsed laser device, the residual electric energy of the pulse charging capacitor (5) is applied to the discharge excitation part (1) after the main discharge is completed. To generate an arc discharge, the main electrodes (la) and (lb) are sputtered by sputtering the metal constituting the main electrodes (la) and (lb).
b) The surface of the discharge excitation section (1) is damaged, the laser gas is contaminated, and the laser gas is decomposed and deteriorated, causing
), which leads to deterioration of performance and reliability and limitation of service life.

This invention was made to solve the above-mentioned problems, and aims to provide a discharge-excited pulsed laser device with high performance and long life by preventing arc discharge between main electrodes.

[Means for Solving the Problems] The discharge-excited pulsed laser device according to the present invention includes a short-circuiting switch connected in parallel to the discharge excitation section, and a short-circuiting switch connected to the short-circuiting switch immediately before the main discharge transitions to arc radiation. A short-circuit activation means for short-circuiting is provided.

[Function] In the present invention, the short-circuit starting means short-circuits the short-circuit switch to flow the residual electrical energy in the charging/circuit to the short-circuit switch before the main discharge ends and transitions to arc discharge. No voltage is applied to the discharge excitation section after discharge ends.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. 1st
The figure is a circuit diagram showing one embodiment of the present invention, and (1) to
(6) is similar to the conventional device described above.

(lO) is a short-circuit switch connected in parallel to the discharge excitation section (1). (11) is a trigger control circuit that controls the activation timing of the high voltage switch (6) and the short circuit switch (10), from when the high voltage switch (6) is activated to when the short circuit switch (lO) is activated. A predetermined time period is set in advance.

A is the charging circuit current flowing from the pulse charging capacitor (5), B is the excitation capacitor current flowing from the excitation capacitor (2), C is the discharge excitation part current flowing between the main electrodes (la) and (lb), D is short circuit switch (10)
The waveform of each current A-D is shown in FIG. 2.

Next, the operation of the embodiment of the present invention shown in FIG. 1 will be described with reference to the waveform diagram in FIG. 2.

First, at timing P, the trigger control circuit (11)
When the high voltage switch (6) is activated, charging circuit current A flows from the pulse charging capacitor (5) to the excitation capacitor (2), and the transfer of electrical energy begins. The electric energy transfer time TI at this time is about 100 ns.

This electrical energy transfer causes the excitation capacitor (2) to
The voltage between both terminals increases, and at timing Q, glow discharge starts between the main electrodes (1a) and (1b). At this time, the excitation capacitor current B (11 energy) inputted from the excitation capacitor (2) becomes the discharge excitation part current C and flows between the main electrodes (la) and (1b). Therefore, during the glow discharge time T2, the laser gas is excited and emits laser light. The above operation is similar to that of the conventional device described above.

Next, at timing R before moving to arc discharge time T3, the trigger control circuit (11) switches the short circuit switch (10
) and short-circuit the short-circuit switch (10).

The predetermined time for determining this timing R is set to about 100 ns to about 10-odd ns from TI+72.

Therefore, during glow discharge time 2, the excitation capacitor (2
), sufficient electrical energy is input to the laser gas, so performance will not deteriorate. Further, since the main discharge is forcibly terminated at timing R immediately before the transition from the glow discharge time T2 to the arc discharge time T3, arc discharge does not occur between the main electrodes (1a) and (lb).

At time T3 after the short-circuit switch (10) is short-circuited, all of the charging circuit current A (residual electrical energy) is consumed as short-circuit switch current via the short-circuit switch.

When repeating the next main discharge, the discharged pulse charging capacitor (5) is charged again. The interval between repeated main discharges is about a few milliseconds, so during that time the short-circuit switch (
10) recovers and becomes open again.

In the above embodiment, the trigger control circuit (11) was provided as a short-circuit starting means, but as shown in Fig. 3, the short-circuit switch (lO) is a laser trigger spark gap, The emitted laser light (I2) may be guided through an optical delay path (not shown) of a predetermined length and used to activate the shorting switch (10). In the figure, (13) connects the laser beam (12) to the short-circuit switch (1
This is a condensing lens that focuses light on 0).

In this case, the optical delay path is composed of, for example, an optical fiber, and the laser beam (I2) is irradiated onto the shorting switch (10) several tens of nanoseconds after the start of laser beam emission, that is, the timing Q of the main discharge opening. The length is set as follows. Therefore, at timing R shown in FIG. 2, the main electrode (1a), (
lb) can be shorted.

Alternatively, a photodetector (not shown) may receive the laser light emitted from the discharge excitation unit (1) and convert it into an electrical signal, and the short-circuit switch (10) may be activated by this electrical signal.

In this case, the photodetector is equipped with a built-in delay circuit for outputting an electrical signal after a predetermined time (several ion seconds) has elapsed after receiving the laser beam, or the photodetector is equipped with a predetermined length of optical It may be configured to receive laser light via a specific delay path.

[Effects of the Invention] As described above, according to the present invention, a short-circuit switch is provided in parallel with the discharge excitation section, and by short-circuiting this short-circuit switch immediately before the main discharge transitions to arc discharge, the main discharge is terminated. Since subsequent arc discharge is prevented from occurring, deterioration of the main electrode and the laser gas is prevented, and a discharge-excited pulsed laser device with high performance and long life can be obtained.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing one embodiment of this invention, Fig. 2 is a waveform diagram showing each current in Fig. 1, Fig. 3 is a circuit diagram showing another embodiment of this invention, Fig. 4 1 is a circuit diagram showing a conventional discharge-excited pulsed laser device. (+)...Discharge excitation part (La), (lb)...
・Main electrode (2)...Excitation capacitor (3)...Pre-ionization gap (pre-ionization mechanism) (5)
...Pulse charging capacitor (6) in the discharge circuit...
- High voltage switch for starting the discharge circuit (10)...Switch for short circuit (11)...Trigger control circuit (short circuit starting means) (12)
) ... Laser light P ... Timing when the charging circuit starts Q ... Timing when main discharge starts R ... Timing when the short circuit switch starts shows. Hanging 1 drawing 2 drawings

Claims (6)

[Claims] (1) A discharge excitation section consisting of a pair of opposing main electrodes and a laser gas interposed between these main electrodes, an excitation capacitor connected in parallel to this discharge excitation section, and a pulsed excitation capacitor A discharge-excited pulsed laser device that includes a pulse charging circuit for charging and a pre-ionization mechanism for pre-ionizing the laser gas, and that generates laser light by main discharge between the main electrodes, connected in parallel to the discharge excitation section. A discharge-excited pulsed laser device comprising: a short-circuiting switch; and short-circuit starting means for short-circuiting the short-circuiting switch immediately before the main discharge transitions to arc discharge. (2) The short-circuit activation means includes a trigger control circuit that controls the activation timing of the pulse charging circuit and the short-circuit switch, and the short-circuit switch is short-circuited after a certain period of time after the pulse charging circuit is activated. A discharge-excited pulsed laser device according to claim 1, characterized in that: (3) The short-circuit starting means is composed of an optical delay path having a predetermined optical path length for guiding the laser light emitted from the discharge excitation part, and the short-circuit switch is configured to conduct The discharge-excited pulsed laser device according to claim 1, wherein the discharge-excited pulsed laser device is activated. (4) The short-circuit activation means consists of a photodetector that detects the laser light emitted from the discharge excitation part, and the short-circuit switch is
2. The discharge-excited pulsed laser device according to claim 1, wherein the discharge-excited pulsed laser device is activated by an electric signal output from the photodetector. (5) The discharge-excited pulsed laser device according to claim 4, wherein the photodetector outputs an electric signal after a certain period of time after detecting the laser beam. (6) The discharge-excited pulsed laser device according to claim 4, wherein the photodetector detects laser light passing through an optical delay path having a predetermined optical path length.