JPS61116889A - Discharge excitation short pulse laser device - Google Patents

Abstract

PURPOSE:To stably operate a laser device even if an oscillating velocity is increased by forming a heat sink fin on the back surface of the second electrode and circulating laser gas in the device by a an when opposing the first main electrode and the second main electrode having a plurality of holes with a laser light axial direction as a longitudinal direction to operate the laser device. CONSTITUTION:The first main electrode 9 mounted on a heat exchanger 12 and the second main electrode 8 having many holes are opposed in a laser housing 15, a laser gas flow 18 is circulated in the housing 15 to cool a laser device. In this structure, the electrode 8 is composed of nickel, an auxiliary electrode 10 interposed through a dielectric 11 of the back surface is formed of alumina, and a heat sink fin 20 is secured thereon. A fluid guide 13 which extends is provided in the housing 15 and at one end of the dielectric 11, and gas flow 18 agitated by a fan 14 is strongly blown to between the electrodes and the fin 20. Thus, the electrode 8 and the dielectric 11 are effectively cooled, and even if the repeating vibration velocity is accelerated, the operation can be stabilized.

Description

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

[Conventional technology]

FIG. 4 is a sectional view showing an excimer laser device as an example of a conventional discharge-excited short pulse laser device. In the figure, ill is a high voltage power supply, +21, +51, (
71 is a capacitor, (3) is a high resistance, (4) is a switch, (6) is a coil, and (9) is placed in the laser gas flow, with the laser optical axis direction (perpendicular to the plane of the paper) being the longitudinal direction. The first main electrode (8) is a second main electrode, that is, the aperture electrode, which is disposed opposite to the first main electrode (91) and has a plurality of apertures; 0 is the aperture electrode (8 ) is placed in close contact with the back surface of the dielectric, (lO) is placed in close contact with this dielectric αυ, and is an auxiliary electrode facing the aperture electrode (8), @ is the heat exchanger, - is a fluid guide, σ4 is a fan, (to) is a laser cylinder, 4 is an insulator, μη is a main discharge space, and (7) is an arrow indicating the direction of the laser gas flow.

Next, FIG. 5 is a plan view of the apertured electrode f81 viewed from the main discharge space, and in the figure, a9 indicates the aperture.

Next, the operation will be explained.

Let's talk about the circuit system without getting carried away. Charge supplied from the high voltage power supply ill is first stored in the capacitor (2).

Next, when the switch (4) becomes conductive, the capacitor (
2), the switch (4), the capacitor (6) via the ground line, and the capacitor (2) via the coil (6).
), the current loop returns to the capacitor (2
) is transferred to the capacitor (6). Along with this rapid charge transfer, the gap between the aperture electrode (8) and the first main electrode (91 (hereinafter referred to as the main discharge electrode gap), and the gap between the aperture electrode (8) and the auxiliary α The voltage between the auxiliary discharges (hereinafter referred to as the auxiliary discharge interval) rises sharply.

The starting voltage of the auxiliary discharge is lower than the starting voltage of the main discharge. Therefore, first, the dielectric surface ((auxiliary discharge (surface radiation)) is A part of the tL molecules generated in this auxiliary discharge and photoionization by ultraviolet light from this discharge field are generated.
The main discharge becomes a glow-like uniform discharge, and then the main discharge occurs in a pulsed manner in the main discharge space ση to excite the laser medium, and as a result, laser light is collected. . The pulse width of this laser beam is mainly 7i12
It depends on the pulse width of '4t, but for example, in an excimer laser, which is one of the short pulse lasers, it is several tens of n5ec. A thyratron is normally used as the switch 4, and the above-mentioned laser pulse oscillation is repeated at a repetition rate of several Hz to several kl (z, usually several hundred Hz).

Next, we will discuss the fluid system. Generally, after the main discharge occurs in a pulsed manner, the main discharge space Uη 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 ση before the pulsed main discharge occurs.

For this reason, a heat exchanger @ is installed to prevent the temperature from increasing due to the discharge of the 7-anq4, fluid guide □□□, and laser gas, and the flow velocity in the main discharge space is usually as high as several tens of meters per second. Gas flow is achieved.

In this conventional example, cooling of the aperture' 4 poles (8) and the fat electrolyte circle is achieved in the back space through turbulent heat transfer by the gas flow (through) and the sleeve support electrode 4i [+u+] on the back surface. This is done only by heat transfer due to the natural convection that is formed. Moreover, the aperture electrode (81 side is a creeping auxiliary discharge and a
While there is electricity, the power becomes heat.

Is large input order as excimer laser interest rate? According to a trial calculation, the laser pulse energy is 200mJ/pulse,
(Considering a model with a v-return speed of 1 kHz and an average output of 200 W, the normal laser oscillation efficiency is 1 ton, so the energy that cannot be stored in the capacitor (2) is 20 kW tonal.11
If the Ohmink loss in the 111M system is halved, it is 1
OKW is put into the gas. Only a few of them are open holes.
l1tffi (Additional part 31, even if it becomes @ source, late g
reaches the order of w.

On the other hand, when we try to calculate the turbulent heat retardation rate, we find that, for example, if we use the analogy of Kurtz/, we can calculate the Kunsert number (
N, denoted as □'), Reynolds number (denoted as R, X).

Brantl attack (denoted as P) 1 local transmissivity < h (denoted as λHa).

From the gas flow upstream side of the aperture electrode (8), various changes in the distance (denoted as Using Maki (1” B
It can be written as (Re) (P r-1) ) [11.

The pressure of He was set to the operating pressure of a normal excimer laser at 3 atm, and the gas flow velocity was 20 m from the flow velocity of a normal excimer laser.
/sec, and the full width of the aperture electrode (8) shape is 0.06to.

The length in the laser optical axis direction is 0.6 m. 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'') is 1.6
' t θ, and since the heat conduction coefficient of gaseous Bruntl is about 0.7 and the heat conduction of helium is 0.13 kca, hloC, the local heat transfer coefficient &hx is 2.6 X 1o2kcaν2 hr'
It is calculated as c.

Now, assuming that the difference between the helium gas temperature and the quality of the perforated electrode (8) is 20°C, the heat dissipated will be about 200W, which is equivalent to or even less than the single-person power mentioned above. 1
I don't have enough M.

For example, at the above-mentioned hardness of 120°C,
If &+gl is made of nickel (which is considered to be a desirable material for excimer lasers), the linear expansion coefficient of 2 is 0.15 x 10-', so the opening pole (8) is 0.2
It will also extend by mm. Generally I-no! Since the structure is such that the pole of the first hole is densely blued to the tormented body u1), the hole electrode (8) does not slide smoothly on the dielectric body 111).
The above elongation often results in an open-hole electrode (810" warpage).

[The problem that the invention attempts to solve]

Conventional discharge-pumped short-pulse laser equipment is configured as shown above, so the average laser output is Improve ω
Therefore, the aperture electrode (81 and the dielectric material S υ are heated, and the fat center body cl) due to M stress is repeatedly applied.
of? The main wave 'I
There are problems such as the gap length between the poles becoming locally uneven and the main discharge easily becoming an arc.

This oscillation I; 1IVi was made to solve the above-mentioned problem, and W1 cools the apertured electrode 1 and the dielectric in a simple manner, thereby increasing the repetition rate/f of laser oscillation.
It is an object of the present invention to obtain a radiation-excited short pulse laser device 11 that operates stably even when the power is increased.

[Means for solving problems]

The discharge-excited short-pulse laser device according to the present invention includes a first main electrode that is disposed in a laser gas flow and whose longitudinal direction is in the laser optical axis direction, and a plurality of first main electrodes that are disposed opposite to the first main electrode. The second main electrode having an opening is disposed in close contact with the back surface of the second main electrode. An auxiliary electrode disposed in close contact with one body and facing the second main itt pole, the dielectric and the auxiliary 1! A constant heat dissipation fin provided on at least one side of the opening, a pulse circuit for applying a pulse voltage between the main poles, and a part forming part of the pulse circuit or independent of the pulse circuit. Is there a voltage between the auxiliary electrode and the second main electrode? It is equipped with a circuit for applying voltage.

[Effect]

The heat dissipation fins in this iJ4K efficiently cool the apertured electrodes and the dielectric fins, as will be explained in detail below.

[JJ! , example]

Hereinafter, an example of this invention will be explained based on the drawings. 1st
FIG. 1A is a blood diagram showing an embodiment of the present invention, and FIG. 1A is a sectional view fc of the main part of FIG. In the figure, CA is a heat dissipation fin, which in this example is provided on the auxiliary electrode (101).

Next, we will explain the operation in detail (open hole electrode (8)).

The dielectric material Qυ and the auxiliary electrode (lO) form a three-layer laminate thermally. For example, the material of the aperture electrode (8) and the auxiliary electrode (lO) is nickel, and the material of the dielectric αD? For alumina, the overall heat transfer coefficient value is 10
It is on the order of 'kcaA%'+n2hr'C, which is two fingers higher than the heat transfer coefficient from the aforementioned opening to the pole (81 to helium gas).

Next, the rate-determining step in cold BJ is the process of heat transfer to the gas (for example, in the excimer laser, more than 90 cm is helium, as mentioned above), and if this process is sped up, it will become more efficient. Good cooling is possible.

Moreover, in order to realize this f″L in a commercially easy way,
It is desirable to use all the laser gas, which is circulated at high speed and divided by fIA in the heat exchanger (14), as a refrigerant to remove evil spirits. First, if the gas flow rate is increased by n times, Reynolds
double, and as a result, the heat transfer coefficient also becomes about n, but on the other hand, the main 7i! ! The pressure center in the electric space Oη is (
This is a problem because it is proportional to the square of the flow velocity), which is n2 times greater.

Therefore, we consider cooling the auxiliary electrode f101k. As mentioned earlier, since the heat level between the hole 4 hole (81), the dielectric material αυ, and the auxiliary electrode (1o) laminate is a big issue, by cooling the auxiliary electrode (101), the side hole' Effective cooling of 4 poles (81 manufactured dielectric material 0υ) (can be used for 1000 minutes).

For this purpose, a heat radiation fin (A) is provided on the auxiliary vehicle (it+o+), and this heat radiation fin 4 is coated with laser gas gold.

Subsidy 1 now! The area of the pole (10) is A, and the area of the fin 121J of this A is the fin temperature; η is attached;
When the heat transfer coefficient of the kJ stack Af+ fin surface is set to ho, the thermal coupling coefficient is given by the following equation.

Here, η is called the fin efficiency and is determined by the heat transfer coefficient of the fin surface, the thermal conductivity of the fin material, the thickness of the fin, and the height of the fin (A).

As is clear from equation (3), by selecting the fin shape so as to increase ηAf, h'l can be made larger by Ic. - Examples are shown below.

Cross-sectional loss of the auxiliary 11 pole (10) Same as the above-mentioned open-hole electrode (8), the width is 0.06 m, and the length in the direction of the laser likely axis force is 0.6 m.
In addition to this, a discharge fin t, a't-2, with a height of 0.02 m and a thickness of 5 mm, a't-2, and the laser optical axis and 1 α
Assuming that 200 sheets are installed in the intersecting direction, A is 0.03
n12. Af&40.48m''.1.If the fin material is nickel and the gas flow rate passing through the fin (E) β part is 20m/s・ec (Yoshibu Kato, Introduction to Yonnetsu, Yokendo edition, 2 )p (1982)), the fin efficiency η is 0.86.The heat transfer coefficient hO on the surface of the fin (A) is 2.6 3.2 X lo'kca
t/rn2hr'(:, which is one order of magnitude larger than the conventional example.

Next, the operation will be explained. The operation of the circuit system will be explained in FIG. 4 and will be omitted at 2 in FIG. 1 for convenience.

First, the laser gas is circulated by the filter 704. The gas leaving the main discharge space opening is cooled to a predetermined temperature by heat exchanger 4 and returned to the main discharge space q7), but a portion of it is auxiliary il! The heat is sent to the heat dissipation fin (4) provided on the back surface of the pole (10) and cools the dielectric (b) and the apertured electrode (8) via the auxiliary electrode (10). Main release 1! space μ
The gases passing through η and the heat dissipating fins are mixed again and guided to the heat exchanger @.

In this actual case, a hole electrode (81, thickness 0-5 mm) was used.
The thickness of the dielectric (6) is 2 mm + the thickness of the auxiliary electrode (lO) is 1 mm, and each i! Pole cross-sectional area, fin size,
The gas flow velocity is the same as the nine used in the trial calculation of the heat transfer coefficient described above. Excimer gas 3 atm (He:Xe:C2-0,15
:0.75:99.1) When oscillating the laser pulse energy room, T/pulse using k, if no heat dissipation fins are provided, the repetition rate is 300H2I7)
At this stage, the gap length between the main discharge electrodes becomes uneven due to warpage due to thermal expansion of the apertured electrode (8), which is mixed with the glow-like main discharge, resulting in a filament-like 7j! In this actual case, even if the speed was repeatedly increased to 400H2, no filamentary discharge occurred, proving the effectiveness of this cooling method. Needless to say, this difference will become even more significant when the repetition rate is further increased to the order of kHz.

FIG. 2 shows another actual case according to the present invention, in which the main discharge space αη and the heat radiation fin (4) section are arranged in series in the gas flow path.

Therefore, when both are arranged in parallel as shown in Fig. 1, the gas flow rate of the fan aΦ is controlled by the heat radiation fin (4).
In contrast, in this actual case, the gas flow rate can be left as is, but the discharge pressure of the fan (b) must be increased. Rather, which form it fits is determined by the fan α beauty performance.

FIG. 3 is a sectional view showing a heat dissipation fin portion according to still another example of the present invention, in which the auxiliary electrode (lO) is embedded inside the dielectric Uυ and has a linear structure. , the radiation fins 4 are provided on the dielectric material υ. The material of the radiation fins 4 in this case may be dielectric or metal.

In addition, in all the above actual cases, the case of excimer laser is mainly explained and the ratio is, but this invention is, for example, TEA 00w.
It can also be applied to other discharge-excited short-pulse lasers, such as lasers, and produces the same effects as in the actual case described above.

However, punching metal, mesh, or the like can be used as the aperture electrode (8), and the shape of the aperture 4 may be oval, polygon, or the like in addition to a circle.

〔Effect of the invention〕

As described above, according to the present invention, the first main electrode is disposed in the laser gas flow and has a longitudinal direction in the direction of the laser optical axis, the first main electrode is disposed opposite to the first main electrode, and the plurality of open A second main electrode having a hole is disposed in close contact with the back surface of the second main electrode, and a second main electrode is disposed in close contact with the dielectric.
forming a part of the pulse circuit; Since the circuit is independent of the pulse circuit and includes a circuit for applying a voltage between the auxiliary electrode and the second main electrode, the second main electrode and the dielectric can be easily connected to the second main electrode and the dielectric. can be efficiently cooled, and as a result, a discharge-excited short pulse laser device that operates stably even at all terms of the repetition rate of laser oscillation can be obtained.

[Brief explanation of drawings]

FIG. 1 (7) is a sectional view showing one embodiment of the present invention.
Figure A) is Figure 1 (main part of force viewed from direction A).
Figure 2 shows another embodiment of this invention.
,, fJ diagram, 3. hot water. . invention. 55. other. Fig. 4 is a cross-sectional view showing a conventional discharge-excited short pulse laser device, and Fig. 5 shows the second main electrode shown in Fig. 4 in the main discharge space. It is a fc plan view seen from the side. In the figure, (8j is the second main electrode, (91 is the first main electrode, (10) is the auxiliary electrode, αV is the dielectric, μs is the arrow indicating the laser gas flow, 4 is the opening, l, 4 is a heat dissipation fin. In each figure, the same reference numerals indicate the same '' or corresponding parts.

Claims (2)

[Claims] (1) A first main electrode disposed in the laser gas flow and having its longitudinal direction in the direction of the laser optical axis; a second main electrode disposed opposite to the first main electrode and having a plurality of openings; an electrode, a dielectric material disposed in close contact with the back surface of the second main electrode, an auxiliary electrode disposed in close contact with the dielectric material and facing the second main electrode, and at least the dielectric material and the auxiliary electrode. A radiation fin provided on one side, a pulse circuit that applies a pulse voltage between the main electrodes, and a part that forms part of the pulse circuit or is independent of the pulse circuit, and is connected to the auxiliary electrode. A discharge-excited short-pulse laser device including a circuit that applies a voltage between second main electrodes. (2) The discharge-excited short-pulse laser device according to claim 1, wherein the radiation fins are disposed in the laser gas flow.