JP3677548B2 - X-ray generator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an X-ray generator suitable for use as an X-ray source of an X-ray apparatus such as an X-ray exposure apparatus, an X-ray microscope, and an X-ray analyzer, and an X-ray apparatus including the X-ray generator.
[0002]
[Prior art]
A so-called laser plasma X-ray source, which is high in luminance and small in size, is an X-ray generator that uses X-rays emitted from the plasma by condensing pulsed laser light on the target material to convert the target material into plasma. Therefore, unlike synchrotron radiation X-ray generators using huge electron storage rings, X-ray exposure devices, X-ray microscopes, X-ray analyzers, etc. are attracting attention as X-ray light sources for production analysis and laboratory-size inspection analysis. Has been.
[0003]
For these purposes, the laser beam converted into X-rays with high efficiency is not only smaller and more practical, but also has higher brightness and is closer to the point light source as much as possible. In addition, since the uniformity of exposure can be improved, a light source with high efficiency, high brightness, and a small spot size is required. In order to realize this requirement with a laser plasma X-ray source, it is better that the density of the target substance is higher, so that a solid is suitable for the target substance.
[0004]
[Problems to be solved by the invention]
However, when the solid target substance is focused and irradiated with pulsed laser light to form plasma, scattered particles emitted from the plasma and the target substance in the vicinity thereof become a problem. Since the target substance is a solid, ionic and atomic scattering particles from the plasma are placed on the surface of an X-ray optical element such as an X-ray reflector or window material arranged to collect and transfer X-rays. The deposited target material significantly deteriorates the reflectivity and transmittance, and the target material in the peripheral portion that has not been heated to the temperature at which it is turned into plasma becomes large scattering particles, and damages the optical element for X-rays by collision.
[0005]
In order to avoid this problem, it is conceivable that the target substance is in the form of gas, liquid, or fine particles (see, for example, Patent Document 1 and Patent Document 2). As long as the liquid is not a volatile substance that does not precipitate on the surface of the optical element for X-rays, the deterioration of the optical element for X-rays cannot be prevented. Therefore, it can be applied only to very limited substances such as water and liquefied gas. It is difficult to liquefy many metal materials that convert X-rays with efficient and useful wavelengths.
An object of the present invention is to provide an X-ray generation apparatus in which the X-ray optical element does not deteriorate even when these solid metal materials are used as a target substance.
[0006]
[Patent Document 1]
JP 2001-023795 A [Patent Document 2]
JP 2001-068296 A
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a shock wave generating means in an X-ray generator that uses X-rays radiated from a plasma by condensing and irradiating a target material with a pulsed laser beam. A shock wave generated in the solid target material is propagated through the solid target material, and the target substance is supplied by utilizing the phenomenon of ejection of the solid target material substance that is generated when released into a vacuum or gas atmosphere. An X-ray generator is provided.
[0008]
The present invention also provides an X-ray generator characterized by using a laser plasma shock wave generated by irradiating a solid target material with another pulsed laser beam in advance as a means for generating a shock wave.
Furthermore, the present invention is not affected by the target material ejected by the X-ray optical element by setting the ejection direction to an angle different from the installation position direction of the X-ray optical element at the target material ejection position. Provided is an X-ray generator characterized by being arranged.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described based on examples with reference to the drawings.
FIG. 1 shows a schematic configuration diagram of an embodiment of the present invention.
In the figure, 1 is a pulse laser beam for generating a shock wave, 2 is a condensing lens, 3 is a solid target material, 4 is a target material extruded from the solid target material 3, and 5 is a pulse laser beam for generating X-rays. 7 represents an optical element for X-rays, 8 represents generated X-rays, and 9 represents a barrier against scattered particles from the plasma for generating shock waves.
[0010]
The solid target material 3 may be the same as a known target material, for example, metal, glass, silicon, or the like. The configuration of FIG. 1 is installed in an atmosphere of vacuum or air or helium gas. Further, 10 represents high-temperature plasma generated by the pulsed laser beam 1, 11 represents a shock wave, 12 represents scattered particles of the high-temperature plasma 10, 13 represents scattered particles of the target substance, and 14 represents collected X-rays.
[0011]
A pulse laser beam 1 for generating a shock wave is condensed and irradiated onto the surface of the solid target material 3 through a condenser lens 2. The focused irradiation intensity at this time is set to a high intensity of about 10 13 W / cm 2 and the pulse width is set to several ns, so that the surface side (surface side) irradiated with the pulse laser beam 1 of the solid target material 3 is irradiated. From the high-temperature plasma 10 of the solid target material 3, and a shock wave 11 is generated toward the inside of the solid target material 3 due to the reaction of the jet.
[0012]
The shock wave 11 propagates inside the solid target material and reaches the side opposite to the surface irradiated with the pulse laser beam 11 for generating the shock wave (back side). At this time, the substance of the solid target material 3 is released from the mutual elastic bond between the atoms from the back side, and becomes an ionic or atomic target substance 4 and ejected at a high density. This ejected target substance is used as a target material (target material) for X-ray generation.
[0013]
FIG. 2 illustrates a streamline diagram as a result of a numerical simulation performed by a computer on the situation in which the target substance 4 for X-ray generation is ejected from the solid target material 3 by a shock wave generated by a pulse laser for generating an impact. The streamlines in the figure represent the situation where the position coordinates of the material substance are moving with time. This is a case in which an aluminum material having a pulse width of 27 ns and a solid target material of 100 μm in thickness is used for the high-intensity pulsed laser beam 1 for generating a shock wave. The vertical axis of the figure shows the space in the thickness (L) direction of the solid target material 3, and the horizontal axis shows the time elapsed after the start of laser light irradiation.
[0014]
From FIG. 2, it can be seen that the shock wave propagates through the solid target material 3 after irradiation of the pulse laser 1 for generating an impact, and a high-density substance close to the solid density is ejected from the back surface. In the example of FIG. 2, the target substance 4 is pushed out from the back surface of the solid target material by about 26 μm at 30 ns after the start of laser light irradiation. Since the empty region of the jet in the back surface is limited to the region where the shock wave reaches the front side of the solid target material, the target substance 4 can be controlled by controlling the condensing region of the pulse laser beam 1 for generating the shock wave. Is possible. By this control, an optimal amount of particulate matter necessary for X-ray generation can be supplied as a target material for X-ray generation.
[0015]
Moreover, the amount of the scattered particles 13 can be greatly reduced by eliminating the excessive amount of the target substance. On the other hand, a large amount of scattered particles 12 are generated from the plasma for generating a shock wave on the surface side, but this can be prevented by providing a physical barrier as shown by a barrier 9 in FIG.
[0016]
The X-ray generation target substance 4 prepared in this way is condensed and irradiated with an X-ray generation pulse laser beam 5 through a condenser lens 6 to convert the target material substance 4 into plasma, Occur. The pulsed laser beam 5 for X-ray generation only needs to be able to instantaneously heat a minute target material 4 for X-ray generation having only a necessary minimum volume to generate X-rays. If the time width of the pulse is short, the energy can be small.
[0017]
Since the shock wave pulse laser beam 1 is irradiated perpendicularly to the surface of the solid target material 3, the shock wave travels in a direction 11A perpendicular to the surface of the solid target material 3. Since the ejected target substance 4 for X-ray generation is accelerated by the shock wave 11, it translates in a direction 4 A perpendicular to the back surface of the solid target material 3. The moving direction of the scattered particles 13 of the target substance 4 for X-ray generation is affected by the energy of the pulse laser beam 5 for X-ray generation.
[0018]
If the energy of the X-ray generation pulse laser beam 5 is not larger than the energy of this translational movement, the scattered particles 13 of the X-ray generation target material 4 are converted into the laser beam 5 by the energy of the X-ray generation pulse laser beam 5. The translation is continued in the direction 13A slightly deflected in the direction of. Therefore, most of the scattered particles 13 generated here move in the translational movement direction 13A. Further, the direction 13A of scattered particles is controlled by the energy of the X-ray pulse laser beam 5, the energy of the shock wave 11, the direction 11A of the shock wave 11, and the ejection direction of the target substance.
[0019]
As shown in FIG. 1, by arranging the X-ray optical element 7 at a position different from the spatial range Z in the direction 13A in which the translational movement is directed, the X-ray optical element 7 is free from the influence of scattered particles. be able to. In other words, by setting the ejection direction of the target material at an angle different from the installation position direction of the X-ray optical element 7, the X-ray optical element is not affected by the target material ejected. it can. The X-rays 14 collected by the X-ray optical element 7 are guided to an X-ray utilization device, an X-ray irradiation device or the like as an output of the X-ray generator of the present invention.
[0020]
In this embodiment, the shock wave generating means is a laser plasma shock generating means. However, other known shock wave generating means, explosives, gas pressure guns, or those using electromagnetic force may be used. Further, although the lenses 2 and 6 are used for condensing the laser beam, these may use other optical elements such as a reflecting mirror, and the X-ray optical element 7 also has the shape of the concave mirror shown in FIG. It is not limited to.
[0021]
【The invention's effect】
According to the present invention, it is possible to prevent an adverse effect caused by scattered particles on an optical element for X-rays without impairing characteristics such as a small size, high efficiency, and a high-intensity point light source inherent in a laser plasma X-ray source as an X-ray generator. . There is no need to process the target material for X-ray generation into gas, liquid, fine particles, etc., and since a substance that is normally solid can be used as the target substance for X-ray generation, a wide range of materials can be selected. Therefore, according to the present invention, it has become possible to produce an X-ray generator that can be easily used in production sites, laboratories, inspection rooms, and the like.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an X-ray generator of an embodiment of the present invention.
FIG. 2 is a streamline diagram of the results obtained by performing a numerical simulation with a computer on the situation where a target material is ejected by a laser plasma shock wave according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Pulsed laser beam for shock wave generation 2 Condensing lens 3 Solid target material 4 Target material for X-ray generation 5 obtained by shock wave ejection X-ray generation pulsed laser beam 6 Condensing lens 7 X-ray optical element 8 X-ray 9 Barrier against scattered particles from plasma for shock wave generation 11 Shock wave 4A Target material substance ejection direction

Claims (3)

In an X-ray generator that collects and irradiates a target laser with pulsed laser light to turn the target material into plasma and outputs X-rays radiated from the plasma,
When the shock wave generated in the solid target material by the shock wave generating means propagates through the solid target material and reaches the interface between the solid target material and the vacuum or gas atmosphere, the shock wave is vacuum or An X-ray generator characterized by being a substance of a solid target material ejected by being released into a gas atmosphere. 2. The X-ray generator according to claim 1, wherein the shock wave generated by the shock wave generating means is a laser plasma shock wave generated by irradiating a solid target material with another pulse laser beam. In the target material ejection position, the ejection direction is set to an angle different from that of the X-ray optical element installation position so that the X-ray optical element is not affected by the ejected target substance. The X-ray generator according to any one of claims 1 and 2.

Images