JPH1073698A - Vacuum ultra-violet spectroscope for laser plasma x ray - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vacuum ultra-violet spectroscope for laser plasma X rays which makes it possible to obtain highly strong X rays easily. SOLUTION: When a target 1 is irradiated with a condensed laser beam, X rays are generated radially from a laser irradiation point 6 on the target 1 and a hollow mirror 2 condenses the X rays. The X rays condensed by the mirror 2 are guided by a flat diffraction grating 3. The X rays dispersed by the diffraction grating 3 are condensed on an output slit 5 by a reflector-type revolution paraboloid mirror 4. This makes it possible to extract X rays of a desired wavelength. More X rays dispersing radially can be condensed and highly strong X rays can be obtained easily by locating the hollow mirror 2 near the laser irradiation point 6 to reflect plasma X rays on the inner surface of the mirror 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray generator for generating X-rays from a plasma induced by irradiating a target with a laser beam. The present invention relates to a vacuum ultraviolet spectroscope for laser plasma X-rays that disperses X-rays.

[0002]

2. Description of the Related Art When a substance is irradiated with a focused laser beam,
X-rays are emitted from the plasma generated by the heat generated by the laser light. Various devices have conventionally been known as vacuum ultraviolet spectrometers for extracting X-rays of a specific wavelength from the X-rays. For example, an example using a Rowland type vacuum ultraviolet spectroscope using an entrance slit and an exit slit [Y.
Horikawa, et al. , Optical E
ngeneering, Vol. 33, No. 5, pp. 1721-172
5 (1994)], an example in which two concave mirrors are used to focus a beam and evaluate spectral characteristics [Yamamoto]
et al. , SPIE 2010, 152- 15
9 (1993)].

[0003] FIG. 3 is a block diagram of a vacuum ultraviolet spectroscope that has been conventionally used. The spectroscope basically includes an entrance slit 11, a diffraction grating 12, and an exit slit 13. White light extracted from the entrance slit 11 is separated by the diffraction grating 12 to form an image on the exit slit 13.
Extract a specific wavelength. To change the wavelength to be extracted, the diffraction grating 12 is rotated. However, when this spectroscope is used for a laser plasma X-ray source, the available X-ray dose is determined by the width of the entrance slit 11, and it is difficult to obtain high-intensity X-rays.

FIG. 4 is a block diagram of another conventional vacuum ultraviolet spectroscope. This spectroscope is of a relatively high efficiency utilizing the small size of the laser plasma X-ray source. The light is split by the diffraction grating 16 installed at the rear. The vacuum ultraviolet light split by the diffraction grating 16 is extracted through the exit slit 17.
The size of the laser plasma X-ray source 14 is usually about several hundreds of μm, and by using this, the entrance slit required in a normal spectroscope can be omitted, and X-rays with relatively high intensity can be obtained. Can be. However, in this spectroscope, the condenser mirror 15 composed of a toroidal mirror or a cylindrical mirror is provided in a chamber different from the plasma X-ray chamber, and it is difficult to collect all the X-rays emitted from the laser plasma. is there.

[0005]

As described above, the conventional vacuum ultraviolet spectroscope for laser plasma X-rays has a problem that the collection efficiency of divergent X-rays is low and only low-intensity X-rays can be obtained. The present invention has been made to solve the above problems, and has as its object to provide a vacuum ultraviolet spectroscope for laser plasma X-rays that can easily obtain high-intensity X-rays.

[0006]

According to a first aspect of the present invention, there is provided a hollow type laser beam collecting a vacuum ultraviolet ray and a soft X-ray generated near a laser irradiation point of a target and guiding the same to a reflection type diffraction grating. A mirror is provided. In this way, by disposing the hollow mirror near the laser irradiation point of the target and reflecting the plasma X-rays on the inner surface of the hollow mirror, more X-rays radiating from the laser irradiation point can be collected. Can be. According to another aspect of the present invention, a condensing mirror is provided between the reflection type diffraction grating and the exit slit.

[0007]

FIG. 1A is a block diagram of a vacuum ultraviolet spectroscope for laser plasma X-rays showing a first embodiment of the present invention. The X-rays handled in the present embodiment are in a wavelength range extending from vacuum ultraviolet rays to soft X-rays, but will be simply described as X-rays in the following description. In this vacuum ultraviolet spectroscope for laser plasma X-rays, a target 1 and a hollow mirror 2 having an inner surface of a paraboloid of revolution are installed in a laser plasma generation chamber (not shown). A plane diffraction grating 3, a reflection-type paraboloid of revolution 4, and an exit slit 5 are provided therein (not shown).

When the focused laser beam is irradiated on the target 1, X-rays are generated radially from a laser irradiation point 6 on the target 1, and the hollow mirror 2 collects the X-rays.
In the present embodiment, a rotating parabolic mirror that is an aspherical mirror is used as the hollow mirror 2. This is shown in FIG.
As shown in (b), a parabola symmetrical with respect to the axis X is cut (portion where the broken line is cut), and the axis X is set as a rotation axis.
It has been rotated 0 degrees.

As the other hollow mirror 2, a cylindrical mirror or a spheroidal mirror as an aspherical mirror may be used. The spheroidal mirror cuts two places similarly to the parabolic mirror, and uses the long axis X as a rotation axis to 360.
It is rotated by degrees. Further, a toroidal mirror which is an aspherical mirror may be used. Furthermore, the reflectivity of X-rays may be improved by performing a multilayer coating on the surface of the mirror.

The X-rays collected by the hollow mirror 2 are guided to a plane diffraction grating 3 provided behind the mirror 2. Although the plane diffraction grating 3 has a function of dispersing X-rays,
There is no function of condensing the split X-rays on the exit slit 5. Therefore, the reflection type paraboloid of revolution 4 is arranged behind the plane diffraction grating 3, and the X-rays separated by the diffraction grating 3 are focused on the exit slit 5. Thus, X-rays of a desired wavelength can be extracted. At this time, take out X
To change the wavelength of the line, the diffraction grating 3 may be rotated.

In this embodiment, a plane diffraction grating is used as the reflection type diffraction grating, but a concave diffraction grating may be used. Next, Table 1 shows the X-ray utilization efficiencies of the conventional vacuum ultraviolet spectrometer and the vacuum ultraviolet spectrometer of the present invention.

[0012]

[Table 1]

In Table 1, a vacuum ultraviolet spectrometer I and a vacuum ultraviolet spectrometer II are conventional vacuum ultraviolet spectrometers shown in FIGS. 3 and 4, respectively, and a vacuum ultraviolet spectrometer III is a vacuum ultraviolet spectrometer of the present invention. It is. In any case, the diffraction grating has 12 grooves.
A beam having a diameter of 00 lines / mm and a size of 50 mm × 50 mm is used, and the exit slit is adjusted to a condition capable of obtaining X-rays having a resolution of about 200 and 10 nm.

In the case of the conventional spectroscope I, the utilization efficiency is 10 ^-7.
(Srad), about 10 ^-4 (sra
contrast in the range of about d), the use of spectrometer III of the present invention, Hakare use efficiency of 10 ^-2 (SRAD), it can be seen that conventional as compared the 10 ² to 10 ⁵ times stronger X-ray is obtained .

Then, it was experimentally confirmed to what degree the X-ray intensity can be improved by using the vacuum ultraviolet spectroscope of the present invention. FIG. 2 shows the intensity of 10-nm wavelength X-rays taken out by a conventional vacuum ultraviolet spectrometer and the vacuum ultraviolet spectrometer of the present invention. Here, a tantalum foil is used as the plasma X-ray generation target 1 and N
d: Laser was condensed on the target 1 by using a lens having a focal length of 400 mm using the second harmonic of YAG.

The conventional vacuum ultraviolet spectrometer is of the high efficiency type shown in FIG.
5 was 10 mm wide and 300 mm long. In the vacuum ultraviolet spectroscope of the present invention, the change in beam intensity was examined by changing the inner diameter of the hollow mirror 2 and the distance between the target 1 and the hollow mirror 2.

As apparent from FIG. 2, in the vacuum ultraviolet spectroscope of the present invention shown by a solid line, the inner diameter of the hollow mirror 2 is 4 m.
It can be seen that the X-ray intensity does not change so much up to about m. Further, the hollow mirror 2 is placed on the target 1 by 0.1 mm.
It can be seen that by approaching to the extent, a beam intensity about five times as large as that when the distance is 1 mm can be obtained. As described above, in the vacuum ultraviolet spectroscope of the present invention, as the hollow mirror 2 installed at the beginning of the optical system is placed closer to the target 1, the light-collecting efficiency is improved, and high-intensity X-rays can be obtained.

According to the vacuum ultraviolet spectrometer of the present invention,
It can be seen that in each case, a beam that is one order of magnitude stronger than that of a conventional vacuum ultraviolet spectrometer can be obtained. In order to achieve such high efficiency with a conventional vacuum ultraviolet spectrometer, it is necessary to use a mirror having a width of several thousand mm and a length of several meters, which is not realistic. 10
Equivalent performance can be obtained with a small device using a small hollow mirror of 0 mm, and an experiment using high-intensity X-rays can be easily performed in a normal laboratory.

[0019]

According to the present invention, the hollow mirror is disposed near the laser irradiation point of the target, and plasma X-rays are reflected on the inner surface of the hollow mirror to radiate radially from the laser irradiation point. Since more X-rays can be collected, high-intensity X-rays can be easily obtained. As a result, it is possible to easily use X-rays generated by laser plasma, and to contribute to X-ray lithography and X-ray microscopy.

Further, by disposing a condensing mirror between the reflection type diffraction grating and the exit slit, for example, a plane diffraction grating having a function of dispersing X-rays but not condensing on the exit slit is provided. Even when a reflection type diffraction grating as described above is used, the X-rays separated by the diffraction grating can be focused on the exit slit.

[Brief description of the drawings]

FIG. 1 is a block diagram of a vacuum ultraviolet spectrometer according to a first embodiment of the present invention and a diagram showing a structure of a hollow mirror.

FIG. 2 is a diagram showing the intensity of X-rays extracted by a conventional vacuum ultraviolet spectroscope and the vacuum ultraviolet spectrometer of the present invention.

FIG. 3 is a block diagram of a conventional vacuum ultraviolet spectroscope.

FIG. 4 is a block diagram of another conventional vacuum ultraviolet spectrometer.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Target, 2 ... Hollow type mirror, 3 ... Plane diffraction grating, 4 ... Reflection type rotation parabolic mirror, 5 ... Exit slit,
6 ... Laser irradiation point.

Claims (2)

[Claims] 1. An X-ray generator for generating X-rays from plasma induced by irradiating a target with a laser beam, and a reflection type diffraction grating for dispersing vacuum ultraviolet rays and soft X-rays and entering the exit slit. In the vacuum ultraviolet spectroscope for laser plasma X-rays provided, a hollow mirror is provided near the laser irradiation point of the target, and collects the generated vacuum ultraviolet rays and soft X-rays and guides them to a reflective diffraction grating. Vacuum ultraviolet spectrometer for laser plasma X-rays. 2. The vacuum ultraviolet spectroscope for laser plasma X-rays according to claim 1, wherein a converging mirror is provided between said reflection type diffraction grating and an exit slit. Vacuum ultraviolet spectrometer.