JPH02256285A - Target for laser oscillation - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a short wavelength recombination plasma laser oscillation device, and in particular, to a solid target for plasma generation suitable for laser oscillation in the soft X-ray region. The present invention relates to a laser oscillation target having a shape that allows high gain of the medium to be obtained.

(Prior Art) When short-pulse high-power laser light is linearly focused onto a solid target, a high-density plasma containing multivalent ions is generated on the target surface.

The generated high-density plasma is ejected from the target surface, expands adiabatically, cools rapidly, and recombines strongly. At this time, population inversion occurs between the excited levels of the multiply charged ions, inducing the oscillation operation of the recombination laser.

In recent years, research on such short wavelength recombination plasma lasers, particularly lasers in the soft X-ray (0.3 nm<λ<30 nm) range, has progressed rapidly. There are mainly three methods considered as excitation methods for soft X-ray lasers. These are the electron impact method, the recombination plasma method, and the photoexcitation method. Among these, the recombination plasma method is thought to have an advantage over other methods in terms of laser oscillation efficiency as the laser wavelength becomes shorter. However, the irradiation intensity of the excitation laser required to generate high-density plasma is 10
It reaches as high as 13 to 1014 W/-, and for example, ultra-high power laser systems used in laser fusion are used. These laser systems are large equipment and require large buildings, and even if it has been experimentally shown that soft X vA lasers are possible in principle, such expensive and large equipment is not necessary. It was difficult to put it into practical use as far as possible.

Therefore, it is expected that the efficiency of laser oscillation will be improved to realize a compact system that can obtain high-energy soft X-ray laser output that can be used for applied research in various fields.

Targets that have been used in conventional recombination plasma laser devices include fiber, foil, and plate types. In these targets, the generated plasma is free to expand in a direction perpendicular to the length of the target, but its expansion is restricted in the length direction. Therefore, in order to ensure expansion of the plasma in the longitudinal direction, a method has been proposed in which the excitation laser beam is discretely cut out using a mask plate to generate plasma spatially and discretely (W
,T,5ifvast,l2.11.5zeto,an
dORWoodll: 8ppl.

Phys, Lett,, vol, 34(3), Feb.

(1979).

(Problem to be Solved by the Invention) However, since the excitation laser of the soft X-ray laser has a very high output, a method of arranging a shielding plate in the optical path cannot be used.

The present invention aims to solve these problems, improve the efficiency of recombinant laser oscillation, and in particular realize a practical compact system that can obtain high output soft X-ray laser.

(Means for Solving the Problem) The above problem is such that concave portions and convex portions are formed on the light irradiation surface of the target to which the pulsed excitation laser beam is line-focused, and the same pulsed laser beam is emitted at the same time. By using a laser oscillation target whose surface is discretely irradiated, high efficiency and large gain can be obtained.

By arranging the target planes discretely, the plasma can expand freely in any direction, which leads to stronger plasma recombination, resulting in high efficiency and large population inversion (
gain).

(Function) FIG. 3 is a conceptual diagram showing the plasma generation process when a laser beam is linearly focused on the target of the present invention having an uneven surface structure. First, when the target 37 is irradiated with the pulsed excitation laser beam 33, high-density plasma 32 is generated from each of the convex portions 31 of the target. Since the same level planes of the target are arranged discretely,
The plasma can expand along the vertical (Y) and longitudinal (X) directions of the line focus of the excitation laser beam 33. In other words, the plasma freely expands from each surface of the discretely arranged targets, and the plasma recombination is strong (occurring), resulting in a large population inversion with high efficiency. These four parts can function as the target convex surface 3.
The second
A plasma 36 is generated. Since this plasma is ejected with a time delay, by utilizing this, it becomes possible to maintain the gain for a long time even when pulsed excitation laser light is used. Therefore, by arranging the targets discretely to enable free expansion and emitting time-delayed plasma41, plasma recombination can be excited for a longer time, resulting in highly efficient and long-term continuous plasma recombination. Population inversion (gain) can be achieved.

(Effects of the Invention) By using the target of the present invention, it is possible to significantly increase the gain of the recombination laser medium, and also to maintain the gain for a long time, making it possible to use a smaller device than before. Laser oscillation with extremely high efficiency has become possible using this method.

(Example) Examples of the present invention will be described in detail below.

FIG. 1' is a block diagram of the entire apparatus for carrying out the present invention. Excitation laser light (λ = 1.053 μl, pulse width 5 ns) oscillated from the Nd-glass laser device 11
, an energy output of 40 J) 12 is reflected by a semi-transparent mirror 13 and introduced into a recombination laser oscillation device 14. On the other hand, the laser transmitted through the semi-transparent mirror 13 enters the laser power monitor 15.

The excitation laser beam is focused by a cylindrical lens 16 provided in the device 13 into a line focus having a line width of 50 μm or less on the surface of the solid target 17.

FIG. 2 is a conceptual diagram showing how a recombination laser (particularly in the soft X-ray laser wavelength range) can be oscillated by line-focusing an excitation laser on the aluminum target of the present invention. As shown in the figure, All Targera-17
is installed so as to be orthogonal to the stripes of the uneven portion with respect to the focus line of the excitation laser beam 12. The shape of the uneven part is
Approximately 0.2 to 1.5 cranes each is preferable. specifically,
The excitation laser is line-focused on a target with a width of 1 crane and 1 fin of concave parts, and the width of the excitation laser is 0.2~0.2 ~
Spectroscopic measurements in the soft X-ray wavelength region were performed at a distance of 1.5 mm. As a result, in the case of a target with the above-mentioned uneven structure, three soft X-ray spectra (13.5 ns,
AES (natural light amplification) of 14.0 fin m, l 4.5 fin m) was observed. Therefore, it is possible to oscillate a soft X-ray laser by adjusting the optical axis of the resonator 18, 18' in the soft X-ray laser wavelength range as shown in FIG. on the other hand,
When a conventional flat target was used, the above-mentioned AES was not detected under these irradiation conditions. This difference is clearly a result of the difference in target structure.

In other words, this is because the free expansion of the plasma was promoted and a stronger recombination state was generated. In addition, since the second target surface is arranged at a position (at the bottom of the recess) that is moderately retreated from the first target surface, which has a discrete arrangement,
A secondary plasma is generated by the excitation laser beam passing through the apertures between the discrete target surfaces. This plasma is suppressed from free expansion, ejects with a time delay, and begins free expansion after reaching the outermost surface (convex portion) of the target. Therefore, this plasma is generated later than the plasma generated from the outermost surface (convex part) of the target.
produces J. By utilizing this, it is also possible to maintain the gain for a long time.

The target is damaged by a single excitation laser irradiation, so a fresh surface is required for each irradiation. Fourth
Figures A and 4B show two types of drum-shaped targets 40a, which are designed to always provide a fresh irradiation surface.
It is a schematic diagram showing 40b. These two drum-shaped targets are placed in the 4A so that they have the same cross-sectional shape as shown in
In the figure, several grooves 41 are formed on the outer periphery, and in Figure 4B,
A plurality of holes 42 along the focus line of the excitation laser
is processed on the outer periphery.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the entire apparatus for carrying out the present invention. FIG. 2 is a conceptual diagram showing how a target of the present invention is irradiated with excitation laser light and a soft X-ray laser is oscillated. FIG. 3 is a conceptual diagram showing the plasma generation process of the present invention, and FIGS. 4A and 4B are schematic diagrams of a drum-shaped target according to the present invention. (Explanation of symbols) 11... Nd-glass laser device, 12... Laser light for excitation, 13... Semi-transparent mirror, 14... Mounting coupling (soft X-ray) laser oscillation device, 15...
...Laser power monitor 16...Cylindrical lens, 17...Target, 31...Target convexity, 32...First plasma, excitation laser beam, target convexity, opening, second plasma . Drafting of drawings (no changes to the content) Figure 2 Cleaning of soft X-ray laser drawings! (No change in content) Figure 4A Figure 4B Figure ■, Display of the case 1999 Patent Application No. 77520 2, Name of the invention Laser oscillation target 3, Person making the amendment Name of applicant related to the case RIKEN 4. Agent 5. Date of amendment order: July 4, 1999. 6. Drawings subject to amendment <Second. Figure 4>

Claims (1)

[Claims] What is claimed is: 1. A target for laser oscillation on which a pulsed excitation laser beam is line-focused, characterized in that a concave portion and a convex portion are formed on the target surface on which the excitation laser beam is line-focused.