JPS6190486A - Short pulse laser device of discharge excitation type - Google Patents

Abstract

PURPOSE:To enable the increase in stability and reliability and the lead-out of large-diameter laser beams by a method wherein the cathode is a conductor having a plurality of apertures, and the cathode and a dielectric are arranged in adhesion, thus generating creeping discharge over the dielectric surface. CONSTITUTION:The cathode 24 is a conductor having a plurality of apertures 25, and the cathode 24 and the dielectric 12 are arranged in adhesion. An auxiliary electrode 14 is arranged so as to be present on the back of the cathode 24 and opposed to the cathode 24 via dielectric 12. Therefore, the throw-in power of reserve discharge and the thickness of a reserve discharge space can be treated as independent factors, and reserve discharge of high throw-in power density over said electric surface is enabled; thereby, uniform glow discharge can be obtained over large widths of the main discharge. As a result, it is possible to increase in diameter of the laser beam and in output, and the electrode structure is simplified. Besides, the heat dissipation of said cathode is facilitated, and this device becomes durable to laser oscillation of high-speed repetition.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention is directed to discharge-excited short-pulse lasers among two-gas lasers, and particularly relates to the seven-pole structure.

[Conventional technology]

In order to obtain laser oscillation 1, it is necessary to perform a spatially uniform discharge in the laser medium.

However, when using short pulse lasers such as excimer lasers and TKACO lasers, the operating pressure of which is a surface pressure of several atmospheres, the discharge tends to converge and become a t-arc.

In order to prevent this, it is customary to perform preliminary ionization to uniformly disperse electron seeds in the main discharge region in advance of the main discharge.

Hereinafter, the conventional technology will be explained based on FIGS. 7 to 10 factors.

7th factor 1 For example (Sato et al., Electronics August issue, 5a1p (19ss)) ty shown in 1.
It is a sectional view showing v pre-ionization type excimer laser vPr1t, in which (1) is a high voltage power supply, (2) is a capacitor, (31rsi [resistance 141H coil/'16
(6a), (6'b) are pre-ionization pins, (7I gap).

(8) is a cathode, (9) is an anode, (101a main radiation R region,
It is a Btuage switch.

FIG.
mbre at &t,, Engineering EKE Journal
of QuantumE180trOniC#: vo
l Ql-9+ NO, 4, 4597 (1973).

M.Blancharcl It at,, Jour
nal Of Applied, Ph7-aica:
vol 45. No, 3.131)F (19)4
)) is a cross-sectional view showing the TKACON laser device shown in FIG.

However, I! in Figure 8! l! The J route system is the same as that shown in FIG. 7, so it is somewhat different from these literature examples. In the figure, α21 is a dielectric, f13 is a capacitor, Q41σ is an auxiliary electrode, O is a mesh cathode, and uG is a pre-discharge area.

FIG. 9 shows a modification of FIG. 8, for example (Y,
Pan at az,, The Review o
f Scientific Instruments:
vox, 43. No, 4.662p (19'72
) of the TEAOO* laser device shown in )! FIG. 3 is a cross-sectional view showing the pole structure. In the figure, a is a Pyrex glass tube, C181 conductor layer, DI is a pre-discharge space, () is a power supply made of iron, a plastic support is raised, and (2) is an insulator.

FIG. 10 is a modification of the field in FIG. 8, and each number f indicates the same part as in factors 2 and 9 of FIG.

Next, the operations of these conventional examples will be explained.

In Fig. 7, the electric charge supplied from the voltage w1 source (ri) is first stored in the capacitor (2). Then, when the switch (1) becomes conductive, the electric charge is supplied from the jitter (2). Switch (II), then connect the anode (9) and pre-ionization pin (6b) via the ground line!D Pre-ionization bottle (6a), capacitor (6) l coil +41fc
The electric charge accumulated in the canonical jitter (2) is transferred to the canonical jitter (6) through the fi loop. During this transfer process, the pre-ionization pin (6a), (6b) Arc discharge 1! occurs across the minute gap I?+ provided at the threshold, and ultraviolet light is generated from this arc discharge. occurs (hereinafter referred to as ultraviolet light pre-ionization), and 1 in the main discharge area + lot.
0'-1a6 electrons/cm' or more are supplied spatially uniformly, suppressing the local growth of a streamer during the main discharge, and suppressing the arc discharge tube. Meanwhile, during this time, the load is still being transferred to the capacitor 161.

The voltage between the cathode (81) and the anode (91) increases. Eventually, when this voltage reaches the breakdown voltage, a spatially uniform pulse discharge occurs in the main discharge region (1 (I) due to the effect of pre-ionization. can get.

Since the infant work shown in FIG. 8 is the same as that shown in FIG. 7 except for the preparation and departure, the operating mechanism of the preliminary g1 ionization will be explained here.

At I21 (pJ) when switch 1)1) is in a conductive state, there is almost no position difference between the MEC cathode ray pole and the auxiliary electrode αI, but when switch (1)1 is in a conductive state, 71! When the transfer of 1! load from capacitor (2) to capacitor (5) begins, mesh m i
A jealous electric field is generated between J51 and auxiliary electric field (141),
In the pre-discharge space cle, a discharge occurs via the dielectric (121) (hereinafter, this process is referred to as an air pre-discharge). It is weaker than that from electric discharge, and the effect of external photon ionization is also weaker.In this conventional example, some of the electrons generated in the preliminary discharge space OG are absorbed by the mesh cathode.
The main beam passing through is directly supplied near the *'* area +1 (mesh cathode 1 in 1 space) 61, and this is the main radiation i! ? 1 for the preliminary electric power that it becomes a Danga that causes it to wake up spatially uniformly.
A circular structure is being considered.

Figure 9 is a modification of the ga diagram, with the auxiliary g pole set as a conductor α,
This was placed in a VG adult Pyrex glass gar+ supported by a plastic support stand 0.

Each of the 4g1) and 1) is held at the same potential by collocating them with a copper power supply wire. Further, the cathode (8) has a structure in which a plurality of protrusions are provided so that an air preliminary discharge can easily occur in the preliminary discharge space 4. The operating mechanism is the 8th above.
It is similar to the one shown in the figure.

FIG. 10 shows the dielectric material a? The auxiliary electrode θ4 was passed through the glass tube for 0 seconds and 7+: Special #I (+71
The operating mechanism is the same as that shown in FIG. 8 above.

By the way, in the conventional examples shown in Figs.
The distance between 7+straddling dielectric 1) and 2' (referred to as the thickness of the pre-discharge space under a) affects the power input to the pre-discharge space (lα or Since the discharge space 05'1 determines the volume of 4, as a result, it is an essential factor for determining the number of electrons per unit area when considered in a plane parallel to the cathode.

In the example of FIG. 8, the anode (91) and mesh cathode c1
Normally, a pre-discharge space t161 is provided which has a thickness smaller than the distance from the pre-discharge space t161. The influence of the thickness of this pre-discharge space OfA was quantitatively observed, and although there are no reported examples, it is clear that there is a tendency as shown below. That is, the above pre-discharge 1) As the thickness of the air barrier OQ becomes thinner, the starting voltage of the air pre-discharge becomes smaller, and the input force into the above-mentioned space (+61) also becomes smaller.
Therefore, when trying to obtain a separation effect with sufficient reserve 1,
It is necessary to provide a certain amount of pre-discharge space (+1) with a thickness t-. However, the main 7f of power dissipated in preliminary discharge
1) From the point of view of laser power efficiency, it is preferable to keep the ratio of power to 1) as low as possible. It is more likely to keep it sufficiently short compared to the distance between the main discharge gap length and the main discharge gap length. Similarly, glass fi171 and IIJG [tll) or mesh $
The structure is such that a preliminary discharge space 4 is provided between the discharge chamber 4a and the discharge chamber 4a.

Next, the conventional pre-ionization mechanism shown in FIGS. 8 to 10 will be described in more detail.

These conventional examples differ from the 7th conventional example in that the main discharge?
1 electronic warehouse discharge machine (IoT
rather than supplying it evenly throughout the space.

Supplied only near the cathode. The effectiveness of this method is explained as follows. That is, for example (J, Eng, L
evatter et at,, Journal o
f AppliecL Phy-eics: vol.
51. No.l, 210F (1980)) to 4
As mentioned, the trap Vc that suppresses the arc emission '4
Po.

Since it is sufficient to prevent the streamer from developing locally due to the effect of the space charge electric field, it is necessary to prevent the streamer from developing locally. As shown in Figure 6, as shown in Figure 6, an electron avalanche is attracted by the seed electron σ# pole (9) and collects in the form of an electron avalanche tAt-. By completely eliminating the local gradient of the electric field, it is possible to prevent the streamer from running out of control.

Therefore, what is the theory of seed electrons per unit plane considering parallel to the cathode? , the ionization effect will be greater if as much as possible is supplied.

[Problem that the invention seeks to solve]

The conventional discharge @starting short pulse laser device configured as above! , each had the following problems.

The nine devices shown in the g'y figure are the main electrodes +81 and +91.
Preparation by ultraviolet light from both sides of 'd1j! [? It is a structure in which ultraviolet light has a fi penetration depth of Ic@ field, and since the width of the live radiation magnetic field (1) cannot be increased, for example, in an excimer laser, it is 6 to 8 mm x 20 to 25 mm.
(!-) I was only able to extract a laser beam with a rectangular cross section.

The conventional example shown in FIG. As mentioned earlier, in this type of column, a1 usually has a dielectric material a
It is provided at a certain distance @rm from z (M, Blan
charcl at at, , , 70urna10
f Applied Physica: VOl,
45. NO, 3, 131) In the example of F (1974), a3mrn) has the following problems: (b) and (b).

P) Metsch cathode u51 and dielectric 1? Of the electrons generated in the space between the two, as many electrons as possible are passed through the mesh cathode 9B+ and supplied to the main discharge area.
It is clear that this method is advantageous in terms of the m effect.

So, 1m of backup electricity! The thickness of Kukan 061 is as brocade as possible.

In other words, if the volume of the pre-ionization space 061 is made smaller, the air pre-discharge input will increase and the mesh cathode 04
The number of electrons generated per unit plane increases when the hole is considered in a plane parallel to The rate at which RF4 is used for recombination is low, so it seems like a tube. However, as already explained in the conventional example Vc, as follows, the thickness of the air reserve'-separate space weight is made thinner, and the input power remains unchanged (if the number of units is increased). It is impossible to do so.

(b) When carrying the laser pulse oscillation and repeating Ifi, the ferrule is heated by the f collision of ions,
This heat grazing! [l# yell. mesh cathode ll6)
Since the space between the a% nitrogen and the dielectric 1) 21 is narrow and there is almost no convection, only heat flow occurs based on the temperature gradient. Therefore, the mesh cathode turtle 1 and the yeast body 12
Although it is advantageous to be as close to each other as possible, this comes at the expense of reducing the input power for the above-mentioned aerial preliminary discharge.

The conventional example shown in FIG. 10 also has similar problems.

In the example shown in FIG. 9, the shape is such that the single molecule generated by the aerial preliminary discharge is easily supplied, but the projections of the cathode 181 and the Pyrex glass It is best to keep the tube aη and tlE- parallel to each other, and to pass it directly through the center of the Pyrex glass tube mouth, where air preliminary discharge is likely to occur in the longitudinal direction of the Odan + JIIO. There are problems in that unevenness occurs in places that are difficult to occur, and that the #E electrode tank structure is complex and difficult to manufacture.

When this light was emitted, agJ could not be achieved due to the aerial breakdown of the rice booster when it was applied to a discharge-excited short-pulse laser bag m which uses a discharge through a dielectric as a preliminary discharge. The factor of the thickness of the pre-ionization space, the four forces of input of the pre-discharge, and the gold are assumed to be independent.

This was done based on the idea that the preliminary discharge Tlt is generated on the dielectric surface (in a thin space), and the A-body has a simple ionization structure, and the main discharge is generated on the dielectric surface. Generate a uniform pre-discharge with high deer density over the corresponding area.

As a result, the purpose is to obtain a laser beam fcit+ that is inexpensive, large-sized, and reliable, and has a large diameter.

[Rounding method to solve problems]

The discharge-excited short-pulse laser device according to the present invention includes a cathode and an anode that are arranged opposite to each other, with the laser optical axis direction being the longitudinal direction. On the main electrode and the back of the above cathode! EE
L, an auxiliary receptacle facing the cathode via an attractant;
Pulse 1) 2 to apply pulse voltage between the above main tjdi
1) M and the above pulse l! l! A discharge-excited short-pulse laser device comprising a circuit that forms part of a circuit or is independent of the pulse TgI heat and applies a voltage between the auxiliary polarization and the cathode. , the cathode has 151 ridges of apertures, and the cathode and the upper &! The structure is such that electrons, which are the seeds of the main discharge generated between the main polarization regions, are distributed by arranging the current visiting body in close contact with the fatty acid body and generating a creeping discharge on the surface of the fatty acid body. .

[Effect]

In such a cathode structure, a pre-discharge σ dielectric (
Since it is contained in the direction along the surface of I21, the discharge sustaining voltage (voltage applied to the discharge field when discharging over a certain creepage distance) σ is determined by the creepage distance.

It does not depend on the thickness of the preliminary release part. therefore.

Increasing the above creepage distance and increasing the υ maintenance voltage will increase the input power, and if the thickness of the preliminary discharge section is made thinner, it will be possible to input a large amount of power into an extremely small volume. As the discharge power density increases, the number of electrons generated per unit area of the dielectric surface increases, and since the pre-discharge part is thin, it is also advantageous to supply the electrons to the main discharge 9. In addition, if the discharge power density f is significantly increased, the ultraviolet light emission band becomes stronger, and the effect of ultraviolet photon charging stripes is also significantly increased. will be given.

In addition to these effects, the cathode and II conductor are all Ir.
7 as shown in Figures 8 and 10.
? Compared to the conventional example, heat dissipation from the cathode is easier, and it can be used for rapid repeated pulsed laser oscillation.

Furthermore, compared to the conventional example shown in FIG. 9, the cathode structure is extremely simple, and the thickness of the pre-discharge space can be set accurately to achieve the effect of healing.

[Actual example]

Hereinafter, as a practical example of this invention, a case where the present invention is applied to an excimer laser will be explained based on FIG.

FIG. 1 (7) is a cross-sectional view and a plan view, respectively, showing a cathode part according to an embodiment of the present invention, which is the same as the conventional example shown in FIG. 8 except for the B pole part. In the figure, CA4
The conductor has a plurality of openings (2), that is, the cathode, and the cathode and the vI4 body are placed in close contact with each other. In addition, the back of the auxiliary electrode a 1 pole @ rfJf16
Vc exists and is arranged to face the cathode @ via the vj adult az, and in this example, the dielectric tl? embedded inside. However, the back side of the cathode (to) refers to the back side rfJ of the surface facing the anode. A play, in this example, sit 1
2' Alumina is used, and the cathode (to) is made of this alumina (
This is a conductive film formed by depositing nickel on No. 121 to a thickness of 5 cm. The opening is formed by etching.

The circuit system is shown in Figure 48 and uses the nine conventional examples and Tou's capacity transfer method. As explained in the conventional example, a capacitance transfer occurs between the two capacitors, and while the voltage between the main electrodes increases, rolling pressure occurs between the cathode @ and the auxiliary electrode 1) 4, Figure 4 ■, what's that?

As shown in the plan view and the th side view, the opening -1 of the cathode @ and the dielectric U? Creeping discharge occurs on the surface of the

Is this creeping discharge ω induced by 0? occurs along the surface,
The extension distance is determined by the voltage applied to the discharge gap (this was previously defined as the sustaining voltage, which is different from the instantaneous voltage applied between the cathode and the auxiliary !thc electrode). 7
Therefore, the sustaining voltage can be increased to 1) 9-plane surface discharge hole part @ all tang metsu.

It does not depend on the thickness of the cathode (which corresponds to the thickness of the creeping radiation i1). As a result, in this embodiment, the thickness of the cathode can be reduced to 20 μmK, and sufficient power can be input to the preliminary discharge (creeping discharge in this example). The table below summarizes an example of the sacrificial conditions at this time, and FIG. 5 shows a schematic fr sectional view of the discharge situation.

The peak current a of the preliminary discharge in this case was 1.2 A/c, and as is obvious, a clean glow-like discharge was obtained with no filament discharge mixed in at all.

In the reported example of the discharge-excited excimer laser by Nakamai,
In contrast to #C, where only the discharge where the width of the main discharge area is smaller than the main discharge gap length is superior, the real Net ff'l
The main discharge gap length (Y6) in the buffer
The effectiveness of the pre-ionization method according to the present invention is demonstrated by the fact that the main discharge area (w) is approximately 1.5 times larger than the main discharge area (mm).

In addition, since the cathode and the fat electrolyte are in close contact, heat dissipation from the cathode is faster than in conventional examples (the cathode does not become red hot even when laser pulse oscillation is performed with rapid repetition). , if the conventional mesh' sag due to red heat like a pole, the arc discharges due to the shortening of the main discharge gap length caused by waviness.
Solve the problem of generating pressure in fl! friend.

In addition, the design is simple, and due to its structure, the thickness of the cathode a and the thickness of the cathode a and the thickness of the creeping surface vl can be easily set in units of m. In addition, there is no need to think about the three spatial arrangements of the dielectric, the cathode, and the 14 poles, just like in the case of low-cost rice! It is only necessary to set the relative position of either the S pole, the negative electrode, or the anode, which is advantageous in manufacturing.

FIGS. 2(7) and 2(G) are new surface and flat dIJ views, respectively, showing a cathode portion according to another embodiment of the present invention. A metal mesh with a thickness of 1 m to 3 mm (100 m in this example) is used as the cathode 0. The dielectric It? On the surface of , @ pole (to)! Figure 1 (75, (
This embodiment is opposite to the embodiment shown in (a), and produces similar effects.

Fig. g3 σ is a sectional view showing the main dt pole portion according to still another embodiment of the present invention. In this embodiment, as typified by the Rogowski type or Chang type, for example, the electric field near the surface of the cathode is gradually relaxed from the center of the cathode to the cathode @! lI electrical conductivity? of#
It has a convex shape in the 91 direction, which can prevent the generation of arcs due to concentration of electric field on the 91-axis direction.

LL In the embodiment shown in FIG. 1, a receptacle transfer type is used as the circuit system, but the circuit system is not limited to this. ! ! e pys g, etc., or the creeping discharge circuit system may be incorporated into the main discharge circuit system.
There is no problem even if both 1!21v& are different and independent.

In addition, as a cathode, nickel is added to alumina, and an opening is created by etching, and the example sentence is i! It is shown in Figure 1, but of course this! ! l! One example, which is not limited to law, is punching metal and hyperelectric body a? It is also possible to place it on top, attach it to the top and crimp it, and there is no problem with other methods as well. The dielectric I? The material is not limited to alumina, but may also be other ceramics, glass, or the like. However, dielectric material 1) 2
The higher the dielectric constant of 1 and the thinner the thickness, the more effective the injection of creeping discharge (support) becomes, which is preferable.

Further, in the above embodiment, the structure is such that the bottom support 141 is brought into close contact with the dielectric body O7, but depending on the case, it may be installed away from the dielectric body O7. However, if 7 is installed at a distance,
! , Since unnecessary discharge will be injected between the auxiliary polarization O (and fat, <body a?), it is better to use the MW body az and eyebrows as much as possible, as in the case of Jokisaiichi. In this case, an integral spun film may be formed on the surface of the N auxiliary electrode to form a long structure.

In addition, the shape of the hole-opening mortar in the above example was set as a circle or a 4-type mesh, but of course, in view of the spirit of the present invention, the hole-opening mortar was
It is not a sound that adds any part to the shape of .

In addition, as a structural factor that affects the creeping discharge depth, the aperture 5 (
4) has a hole diameter of w, which is related to the power density of creeping discharge ω.
The thickness of the cathode is a factor in the formation of the cathode, but the l! The important point, creeping discharge (towards), is predicted w1! By using it as an i-electron, the hole flaw in the opening (which is a factor that determines the maximum sustaining voltage) and the thickness of the cathode (which is a factor that determines the # of the pre-discharge space) can be optimized for pre-ionization. In view of the fact that they can be independently set so as to give the desired effect, there is no limit placed on these two structural factors. However, regarding the cathode, it will be bombarded by ions during the main discharge, so if it is too thin, there will be a problem in terms of life, so it will need to be 1 μm or more, and if the cathode is too thick, it will cause problems As the input power -K becomes lower, it also becomes a hindrance to supplying it to the 1jl area of the main power supply.
3mm g or less is desirable. Further practical use, 10prn
It is preferable to use one with a diameter of ~2 mm.

Finally, although the above embodiment has been explained using an example of application to an excimer laser, of course TEAC! Needless to say, it is also applicable to other lasers such as OII lasers.

However, in Ex 7 Male Laser a.

The current situation is that the discharge is more clumsy than that of the TICACO laser, and that the main discharge is only available to those who use it.

On the other hand, the length of the main discharge gear? In order to increase the laser output, there was a great deal of competition over the applied circuit pressure, so there was a limit in terms of V and source voltage, and in order to increase the laser output, there was a strong desire to widen the width of the main discharge.

Against this background, a misfire has a considerable effect on an excimer laser, making it possible to increase the laser output and increase the diameter of the laser beam.

[Electrodynamics of invention]

As described above, according to this explanation, the cathode is a body with a plurality of openings tV, and the auxiliary tank and the body are arranged in close contact with the body, and the body is Creeping radiation %Il on the surface
By generating , the electrons that become the seeds of the main discharge generated at the raw Vt+Ji threshold are distributed.
The power input for pre-discharge and the thickness of the pre-discharge space can be treated as independent factors, making it possible to perform pre-discharge with a density of 1% on the surface of the above-mentioned body. With this, it is possible to obtain a uniform glow-like discharge f over a wide generation. As a result, it is possible to increase the diameter of the laser beam and increase the output, and the electrode structure is also simplified, making it easier to dissipate heat from the cathode and making it possible to withstand rapid repeated laser oscillations. This also has the effect of improving the reliability of the V-za.

[Brief explanation of drawings]

FIG. 1(7), b) is a cross section S2 and a schematic plan view showing the *+M portion of a cotton example of the present invention, and FIG.
7) and (a) are respectively a cross-sectional view and a schematic plan view showing a cathode portion according to another example of the present invention, and figure 3 is a cross-sectional view showing a live electrode portion according to still another example of the present invention. Figure, Figure 4 ■, Ge) are the appearance of creeping discharge respectively? 5 is a plan view and a cross-sectional view, and FIG.
Figure 6 is a midnight diagram explaining the evolution mechanism of an electron avalanche, Figure 7
Figures 8 and 8 are cross-sectional views showing a conventional discharge-excited short-pulse laser device 1t, and Figures 9 and 10 are cross-sectional views showing the main part of a conventional discharge-excited short-pulse laser device 1t, respectively.
FrIfiegJteal. M Ic # vs Te, (81, Q5J, 124
fl cathode, I91#-j anode, (1z is di-1, 04
) σ auxiliary clearance, (c) trenching discharge in the hole area, and field creeping discharge. It should be noted that in each figure, the reference numeral 8a indicates the corresponding portion.

Claims (6)

[Claims] (1) A main electrode consisting of a cathode and an anode arranged opposite to each other with the laser optical axis direction as the longitudinal direction, and an auxiliary electrode located on the back side of the cathode and facing the cathode with a dielectric interposed therebetween. and a pulse circuit that applies a pulse voltage between the main electrodes, and a pulse circuit that forms part of the pulse circuit or is independent of the pulse circuit and applies a voltage between the auxiliary electrode and the cathode. In the discharge-excited short-pulse laser apparatus, the cathode is a conductor having a plurality of openings, and the cathode and the dielectric are arranged in close contact with each other, and the dielectric surface 1. A discharge-excited short-pulse laser device, characterized in that it is configured to distribute electrons that become the seeds of the main discharge generated between the main electrodes by generating a creeping discharge. (2) A discharge-excited short-pulse laser device according to claim 1, in which a perforated metal plate having a thickness of 1 μm to 3 mm is used as a cathode. (3) A discharge-excited short pulse laser device according to claim 1, which uses a metal mesh having a thickness of 1 μm to 3 mm as a cathode. (4) The discharge-excited short pulse laser device according to claim 1, wherein the cathode is a conductive film formed on a dielectric material. (5) Any one of claims 1 to 4, wherein the cathode and dielectric are shaped to be convex toward the anode so that the electric field near the cathode surface is gradually relaxed as it moves away from the center of the cathode. A discharge-excited short pulse laser device according to claim 1. (6) The auxiliary electrode is in close contact with the surface of the dielectric material opposite to the surface to which the cathode is in close contact, or is embedded within the conductor. The discharge-excited short-pulse laser device according to any one of Items 1 to 9.