JPS6364069B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention is directed to discharge-excited short pulse lasers among gas lasers, and particularly relates to an electrode cooling structure thereof.

[Conventional technology]

FIG. 3 is a sectional view showing a conventional discharge-excited high repetition short pulse laser device, taking an excimer laser, which is one type of short pulse laser, as an example. In the figure, 1 is a high voltage power supply, 2 is a capacitor, 3 is a high resistance, 4 is a switch, 5 is a capacitor, 6 is a coil, 7 is a capacitor, 8 is a hole electrode, 9 is an electrode, 10 is an auxiliary electrode, 11 12 is a heat exchanger; 13 is a fluid guide; 14 is a fan; 15 is a laser housing; 16 is an insulator; 17 is a main discharge space;
8 is a gas flow.

FIG. 4 also shows the main discharge space 1 of the apertured electrode 8.
7 shows the appearance in the direction facing 7. In the figure, 19 is an opening, and the other symbols are the same as in FIG. 3.

Next, the operation will be explained. First, let's talk about the circuit system. The charge supplied from the high voltage power supply 1 is
First, it is accumulated in capacitor 2. Next, when the switch 4 becomes conductive, the electric charge accumulated in the capacitor 2 is transferred to the capacitor 5 due to a current loop in which the current flows from the capacitor 2 to the switch 4, via the ground line, through the capacitor 5, through the coil 6, and back to the capacitor 2. will be migrated.
With this rapid charge transfer, the gap between the aperture electrode 8 and the electrode 9 (hereinafter referred to as the main discharge electrode gap) and the gap between the open hole electrode 8 and the auxiliary electrode 10 (hereinafter referred to as the auxiliary discharge electrode gap) ) voltage rises sharply. Since the starting voltage of the auxiliary discharge is lower than the starting voltage of the main discharge, an auxiliary discharge (creeping discharge) first occurs on the dielectric surface in the aperture 19 provided in the apertured electrode 8. A part of the electrons generated in the auxiliary discharge and electrons generated by photoionization by the ultraviolet light generated from the discharge become seeds for making the main discharge into a glow-like uniform discharge, and then in the main discharge space 17. A main discharge occurs in a pulsed manner to excite the laser medium, and as a result, laser light is extracted. The pulse width of the laser beam depends on the pulse width of the main discharge, and for example, in an excimer laser, which is one of short pulse lasers, it is several nanoseconds. switch 1
1, a thyratron is usually used, and the above-mentioned laser pulse oscillation is repeated at a repetition rate of several Hz to several KHz, usually several hundred Hz.

Next, we will discuss the fluid system. Generally, after a pulsed main discharge occurs, the main discharge space 17 is in a non-uniform state both thermally and in terms of charge distribution, and the next pulsed main discharge is likely to become an arc.
It is necessary to replace the laser gas in the main discharge space 17 before the next pulsed main discharge occurs. For this purpose, the fan 14, the fluid guide 13, and the heat exchanger 1 for preventing temperature rise due to laser gas discharge are used.
2 are disposed, and a high-speed gas flow 18 with a flow velocity of several tens of meters per second in the main discharge space is normally achieved.

In this conventional example, the open-hole electrode 8 and the dielectric 11 are cooled by turbulent heat transfer by the gas flow 18 and heat transfer by natural convection formed in the back space via the auxiliary electrode 10 on the back side. It is only done once. Moreover, the open-hole electrode 8 side becomes a heat input surface while the creeping auxiliary discharge and the main discharge occur.

When calculating the order of heat input using an excimer laser as an example, the laser pulse energy is 200 (m
j/pulse), average output at a repetition rate of 1KHz
Considering a 200W model, the laser oscillation efficiency is usually 1%, so the energy stored in the capacitor 2 is 20kW. If the ohmic loss in the circuit system is halved, 10kW will be injected into the gas. Even if only a few percent of this becomes a heating source for the open-hole electrode portion, it reaches the order of several hundred watts.

On the other hand, if you try to calculate the turbulent heat transfer coefficient, for example (Yoshiro Koto, Introduction to Heat Transfer, Yokendo Edition, 116p (1982))
From, using Kalman's analogy formula, we can obtain the Nutsselt number (denoted as N _U ^x ), the Reynolds number (denoted as R _e ^x ), the Brunttle number (denoted as P _r ), and the local heat transfer coefficient h ^x
), the thermal conductivity of the fluid (denoted as λ He), the thermal conductivity of the fluid (denoted as λ _He ), and the gas flow upstream side of the open-hole electrode. Using various _variables such as ^the distance ₍ ^{denoted as .8} _e・Pr/{1 +B(R ^x-0.1 _e )(P _r −1)} (1) B=0.86(1+l _o [(1+5P _r )/6]/(P _r −1))(
2) can be written as

The pressure of He is the operating pressure of a normal excimer laser 3
The atmospheric pressure was set to 20 m/sec, and the gas flow velocity was changed from the flow velocity of a normal excimer laser to 20 m/sec, and the aperture electrode shape was changed to a width
0.06m, and the length in the laser optical axis direction is 0.6m. now,
If we set 0.03 m as the point of distance x, that is, the center of the electrode width, the Reynolds number (R _e ^x ) is 1.6
×10 ⁴ , and the Prandtl number of the gas is approximately 0.7, and the thermal conductivity of helium is 0.13 Kcal/ _mhr °C, so the local heat transfer coefficient h ^x is calculated as 2.6 × 10 ² kcal/ ^m2 h _r °C. Ru.

Now, the difference between the helium temperature and the open-hole electrode temperature is 20℃.
Then, the amount of heat removed will be approximately 200W,
It only meets or is less than the heat input mentioned above. On the other hand, at the above set temperature difference of 20°C, if the aperture electrode is made of nickel (which is considered to be a desirable material for excimer lasers), the aperture electrode will be 0.2 from its linear expansion coefficient of 0.15×10 ^-4 .
It will also increase in mm. Generally, the aperture electrode has a structure in which it is brought into close contact with the dielectric material, so that the aperture electrode does not slide smoothly on the dielectric material, and the above-mentioned elongation often appears as "warpage" of the aperture electrode.

[Problem that the invention seeks to solve]

Conventional devices are configured as described above, so when the repetition speed is increased to improve the average laser output, the aperture electrode and dielectric are heated, causing damage to the dielectric and warping of the aperture electrode due to thermal stress. This caused problems such as the gap length between the main discharge poles becoming locally uneven, and the main discharge easily becoming an arc.

This invention was made to solve the above-mentioned problems, and it cools the open-hole electrode and dielectric material in an efficient manner, thereby achieving stable operation even when the repetition rate of laser oscillation is increased. The purpose of this invention is to obtain a discharge-excited short pulse laser device.

[Means for solving problems]

The discharge-excited short-pulse laser device according to the present invention has a dielectric having a tube structure, and a cooling medium is sealed inside the tube or is caused to flow through the hole electrode.
It is designed to perform cold equalization of the dielectric and auxiliary electrodes extremely efficiently.

[Effect]

The open-hole electrode, dielectric, and auxiliary electrode can be thermally regarded as a three-layer laminate. For example, if the open-hole electrode and the auxiliary electrode are made of nickel, and the dielectric is made of alumina, the overall The value of the heat transfer coefficient is on the order of 10 ⁴ Kcal/m ² h _r °C, which is two orders of magnitude larger than the aforementioned heat input.

Therefore, if the dielectric material is made into a tube structure and the auxiliary electrode or dielectric material is directly cooled by sealing or flowing a cooling medium inside the tube, it is possible to cool the auxiliary electrode or the dielectric material very quickly and efficiently, including the open-hole electrode. It becomes possible to do this.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. In Fig. 1, 8 is an aperture electrode, 9 is an electrode, 1
1 is a dielectric, 17 is a main discharge space, and 20 is deionized water.

The dielectric 11 has a tube structure. An auxiliary electrode 10 is installed inside the electrode, and deionized water 20 is flowed therein, and the deionized water 20 cools the auxiliary electrode 10 and the dielectric 11, and cools the aperture cathode 8 through them. It is done.

The heat transfer coefficient between deionized water and the auxiliary electrode 10 is
10 ³ Kcal/m ² h _r ℃ or more, and the auxiliary electrode 10,
The heat transfer coefficient of the three-layer laminated structure of the dielectric 11 and the apertured cathode is 10 ⁴ Kcal/m ² h _r ℃ as mentioned above, so if you compare the order of the heat input mentioned above, It is clear that it is possible to keep the temperature of the three-layer laminate almost equal to the temperature of the deionized water.

FIG. 2 shows another embodiment of the present invention, in which reference numeral 21 indicates a power supply line, and other symbols are the same as in FIG. 1. In this embodiment, the auxiliary electrode 10 is excluded,
The deionized water 20 itself has a role as an auxiliary electrode along with a cooling medium, and voltage is supplied through a power line provided in the deionized water, and the auxiliary electrode part has an extremely simple structure. be.

Furthermore, in addition to the deionized water 20, ammonia, fluorinated halogenated hydrocarbon type refrigerant, etc. may be used as the cooling medium.

Furthermore, the cooling operation may be performed by enclosing these cooling media in the dielectric 11 to form a heat pipe.

〔Effect of the invention〕

As described above, according to the present invention, the dielectric material has a tube structure, and the cooling medium is sealed or flowed inside the tube, so that the apertured electrode and the dielectric material can be efficiently cooled. As a result, a discharge-excited short pulse laser device has been realized which has a high repetition rate of laser oscillation, that is, a high average output, and which can operate stably even during high-speed repetition oscillation.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing a discharge-excited short pulse laser device according to one embodiment of the present invention, FIG. 2 is a cross-sectional view showing another embodiment of the present invention, and FIG. 3 is a conventional discharge-excited short pulse laser device. FIG. 4 is a cross-sectional view showing the laser device, and is a configuration diagram of the dielectric and the apertured electrode. In the figure, 8 is an open-hole electrode, 9 is an electrode, 10 is an auxiliary electrode, 11 is a dielectric, 20 is deionized water, 2
1 is a power supply line. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. A main discharge comprising a pair of electrodes whose longitudinal direction is the laser optical axis direction and which are arranged to face each other, and one of the electrodes has a plurality of openings. a pair of electrodes, a dielectric part on the back side of the aperture electrode and in direct contact with the aperture electrode, and an auxiliary electrode in direct contact with the dielectric part so as to narrow the dielectric part. a pulse circuit for applying a pulse voltage between the main discharge electrodes, and forming a part of the pulse circuit, or
and a circuit system that is independent of the pulse circuit and has a circuit for applying a voltage between the auxiliary electrode and the aperture electrode. The dielectric part has a tube structure, and an auxiliary electrode is brought into direct contact with the inside of the tube and on the back side of the surface of the tube that is in direct contact with the open-hole electrode, and a cooling medium is sealed inside the tube. 1. A discharge-excited short pulse laser device characterized in that the discharge-excited short-pulse laser device is configured to be able to circulate through the laser beams. 2. The discharge-excited short pulse laser device according to claim 1, wherein deionized water is used as the cooling medium. 3. The discharge excitation short pulse according to claim 1, characterized in that deionized water is used as the cooling medium, the auxiliary electrode is excluded, and the deionized water itself is used as the auxiliary electrode. laser equipment. 4. The discharge-excited short-pulse laser device according to claim 1, wherein ammonia or a fluorinated halogenated hydrocarbon-based coolant is used as the cooling medium. 5. Claims characterized in that ammonia or a fluorinated halogenated hydrocarbon-based refrigerant is used as a cooling medium, and these cooling mediums are sealed in a dielectric tube to constitute a heat pipe. 2. The discharge-excited short-pulse laser device according to item 1.