JPH08167753A - X-ray preparatory ionization discharge excited gas laser apparatus and its oscillating method - Google Patents

Abstract

PURPOSE: To miniaturize an X-ray preparatory ionization discharge excited gas laser apparatus, to lower the operating voltage, to reduce the Power demand, and to enhance the safety by generating X-rays with high efficiency. CONSTITUTION: An X-ray generating laser beam 2 generated by an X-ray generating laser apparatus 1 is focused linearly by a cylindrical mirror 3, penetrates a total reflection mirror 9, and irradiates a discharging electrode 5. A part of the discharging electrode 5 becomes plasma by a laser beam, and X-ray is generated. By this X-ray, the gas in the space between discharging electrodes 5 and 6 is ionized. A laser beam 8 is oscillated by applying high voltage to the discharging electrodes 5 and 6 with a high-voltage power source 11 synchronized with the X-ray generating laser apparatus 1, and exciting the gas inside the laser container 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge excitation gas laser device, and more particularly to an X-ray preionization discharge excitation gas laser device.

[0002]

2. Description of the Related Art Conventionally, discharge-excited gas laser devices of this kind have realized glow discharge for uniformly and stably exciting the laser medium by ionizing the laser medium prior to the discharge for exciting the laser medium. , Used for the purpose of obtaining laser oscillation with high efficiency.

It is difficult to cause a glow discharge by simply applying a high voltage to the laser gas, and it is necessary to ionize the laser gas by some means to generate electrons in the gas prior to the discharge in order to achieve a stable glow discharge of the laser gas. Is essential. The ionization of gas prior to this discharge is called preionization.

Since the oscillation efficiency of the gas laser depends on the number density of electrons generated by preionization (for example, "eye
IEEE J. Quantum E
electronics QE-20 (3) 198 (19)
84) ")), in order to operate the gas laser with high efficiency, it is necessary to generate the minimum required electron number density by preionization.

Means for preionization are roughly classified into those by irradiation with X-rays and those by irradiation with ultraviolet light, and they are called X-ray preionization and UV preionization, respectively. Here, X
A conventional technique of the line preionization system will be described.

In the case of X-ray preionization, the laser gas in the discharge space is irradiated with X-rays from the X-ray generator prior to discharge, and electrons are generated in the gas mainly by the photoelectric effect and Compton effect. Since X-rays have higher transparency to laser gas than ultraviolet light, the laser gas can be uniformly preionized.
For details on X-ray preionization, see "Laser Research Volume 12, 3
No., pp. 3-13 (1984) ”.

FIGS. 3A and 3B show the conventional X
It is a typical block diagram of a line preionization type discharge excitation gas laser device. Electrons generated at the cathode 12 are accelerated by the electric field generated by the high voltage 18 and collide with the target 13 to generate X-rays 14 by braking radiation. The generated X-rays 14 pass through the discharge electrode 15 that also serves as an X-ray window, irradiate the discharge space between the discharge electrode 15 and the discharge electrode 16 arranged to face the laser gas, and the laser gas sealed in the laser container 17 is discharged. Ionize. The inside of the preionization device is in a vacuum or in a state close thereto so that accelerated electrons are not scattered. On the other hand, since the interior of the laser container 17 is filled with gas, a differential pressure is applied to the discharge electrode 15 which also serves as an X-ray window.

The transmittance of X-rays to a substance is 100 · e
xp [− (ρ / μ) ρt]%. Here, ρ / μ is the mass absorption constant, ρ is the density of the substance, and t is the thickness of the substance. It is empirically known that the mass absorption constant is a constant peculiar to a substance and is proportional to the fourth power of the atomic number Z of the substance and to the third power of the wavelength λ of X-ray (for example, Tokyo Book). Issued "Atomic Physics I" by Spornski, p. 99).
Therefore, the smaller the atomic number Z and the shorter the X-ray wavelength, the smaller the mass absorption coefficient and the larger the X-ray transmittance of the substance. Moreover, the thinner the thickness t of the substance, the greater the X-ray transmittance of the substance.

When aluminum (having a density of 2.7 g / cm ³ ) having a small mass absorption coefficient and excellent X-ray permeability is used for the partition walls of the X-ray generator and the laser device, the thickness is 1
Assuming mm, even hard X-rays with a wavelength of 0.07 nm are 80
% Is absorbed and 20% is irradiated in the gas.
With a hard X-ray having a wavelength of 0.1 nm, 97% or more is absorbed, and less than 3% is irradiated in the gas. The mass absorption coefficient increases as the wavelength of X-rays increases, so X
The transmittance of the line drops sharply. In addition, long wavelength components are absorbed in the X-ray spectrum after passing through the aluminum partition wall, and most of the hard X-rays having a short wavelength are used.

The X-ray generation efficiency η is experimentally expressed by the following equation and is proportional to the acceleration voltage. η = 1.1 × 10 ⁻⁷ VZ Here, V is the acceleration voltage, and Z is the atomic number of the target. In addition, the wavelength spectrum of the generated X-rays has a wide band,
The shortest wavelength λ _S of the generated X-rays is given by the following equation. λ _S = hc / eV where h is Planck's constant, c is the speed of light, and e is the charge of the electron. As the acceleration voltage V is higher, X-rays are generated with higher efficiency, and since the wavelength is shorter, the mass absorption constant for a substance is smaller and the transmittance for the discharge electrode is higher.

In the conventional X-ray preionization discharge excited gas laser device, it is necessary to increase the voltage V in order to obtain the preionization electron density required for highly efficient operation of the laser. The high voltage V is usually several tens kV to several hundreds tens kV, though it depends on the type and pressure of the laser gas.

[0012]

This conventional preionization device for a discharge excitation gas laser has a low X-ray generation efficiency.
Even with a 00 keV electron, it is about 0.8%. Further, since X-rays are radiated from the outside of the laser device, when passing through the tube wall of the container that separates the X-ray generation device from the laser container and the electrode, part of them is absorbed and does not contribute to ionization of gas. Further, the X-rays that pass through the partition and are applied to the gas have a short wavelength, have a small absorption coefficient for the laser gas, and most of the X-rays are not absorbed by the gas, so that they do not contribute to the ionization of the gas and the X-ray utilization efficiency is low. As a result, in order to obtain the required electron number density, a large amount of electric power is required, and a device including a power source becomes large and expensive.

Further, since the generated X-rays include hard X-rays having a high transparency of 0.1 nm or less, it is necessary to shield the X-rays, which makes the device complicated and expensive, and is safe. Lack. Usually, it is necessary to cover the entire device including the X-ray generator and the laser device with a lead plate having a large Z number.

Further, since a high voltage of several tens of kV or more is used in the X-ray generation part, the device including the power source becomes large and expensive, and the safety is poor.

[0015]

SUMMARY OF THE INVENTION It is an object of the present invention to improve the efficiency of generating X-rays, reduce the size of the X-ray preionization device by improving the utilization efficiency, lower the operating voltage, improve the safety, and improve the electricity consumption of the entire laser device. An object of the present invention is to provide an X-ray preionization discharge excited gas laser device which realizes improvement in efficiency.

Another object of the present invention is to provide a method of oscillating the above X-ray preionization discharge excited gas laser device.

An X-ray preionization discharge excitation gas laser device of the present invention is a discharge excitation gas laser device having an electrode therein, an X-ray generation laser device for preionizing a laser gas medium of the discharge excitation gas laser device, An optical system for condensing the laser light generated from the X-ray generation laser device and for entering and condensing the laser light inside the discharge excitation gas laser device.

Further, the oscillation method of the X-ray preionization discharge excitation gas laser device of the present invention is a discharge excitation gas laser device having an electrode inside, and for X-ray generation for preionizing the laser gas medium of the discharge excitation gas laser device. In an X-ray preionization discharge excitation gas laser device having a laser device and an optical system for condensing laser light generated from the X-ray generation laser device, and entering and condensing into the discharge excitation gas laser device, Prior to excitation of the laser gas medium by electric discharge, laser light generated by the X-ray generation laser device is made incident and focused inside the discharge excitation gas laser device by the optical system, whereby X-rays are generated inside the discharge excitation gas laser device. Is generated, and the laser gas medium is preionized by the X-ray.

[0019]

In the present invention, the X-ray generating laser light is focused inside the gas laser container of the discharge excitation gas laser device and emitted from the plasma generated inside the gas laser container.
The lines pre-ionize the laser medium gas.

Since the X-rays for preionization are generated inside the laser container, there is no absorption loss of X-rays generated when irradiated from outside the laser container as in the prior art, and all the generated X-rays are converted into gas. Is irradiated.

The generated X-ray spectrum contains a long wavelength component of 10 nm or more, and these are efficiently absorbed by the laser gas, so that the gas is efficiently ionized.

Further, by adjusting the condensing intensity of the laser and selecting the target material, it is possible to suppress the generation of hard X-rays having high transparency.

[0023]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of an X-ray preionization discharge excited gas laser device of the present invention. This apparatus condenses an X-ray generating laser apparatus 1 for pre-ionizing a laser gas medium, a discharge excitation gas laser apparatus 7, and a laser beam 2 generated from the X-ray generating laser apparatus 1, and discharge discharge excitation gas laser apparatus. 7 has an optical system 3 for entering and condensing the light. Prior to the excitation of the laser gas medium by the electric discharge, the laser light 2 generated by the X-ray generation laser device 1 is made incident on the inside of the discharge excitation gas laser device 7 by the condensing optical system 3 and is condensed inside the discharge excitation gas laser device. X-rays are generated and the laser gas medium is preionized by the X-rays.

The X-ray generating laser device 1 for generating the X-ray generating laser light 2 is required to be capable of generating a high peak light output pulse. For example, solid-state lasers such as YAG laser, LiSAF, LiCAF, LiSC
AF, Ti: Sapphire, Forsterit
e, tunable solid-state lasers such as Alexandrite, liquid lasers such as dye lasers, CO ₂ ,
Examples of the gas laser include CO, a nitrogen laser, and an excimer laser, and a semiconductor laser whose output is being increased in the future. It is desirable that the wavelength has a small absorption and scattering of laser gas, and from that viewpoint, it is generally difficult to use the same type of laser device as the discharge excitation gas laser device 7 that oscillates by preionization as the X-ray generation laser device 1. is there. In addition, a laser with an oscillation line in the infrared region, which has a long wavelength, generally has less scattering than an excimer laser with an oscillation line in the ultraviolet region. It is necessary to select a laser device. With a wavelength tunable laser, the oscillation wavelength can be set so as to avoid the absorption wavelength of the laser gas.

The discharge excitation gas laser device 7 comprises a laser container 4 in which a laser gas is sealed, discharge electrodes 5 and 6 are provided inside the laser container 4, and a high voltage power source 1 is provided outside the laser container 4.
One. The discharge electrodes 5 and 6 have a semicircular cross section as shown in FIG. 2 and extend in the axial direction of the resonator.

A total reflection mirror 9 and an output mirror 10 are provided at both ends of the laser container 4, and the total reflection mirror 9 and the output mirror 10 form a resonator to generate a laser beam 8. The total reflection mirror 9 has a high reflectance with respect to the wavelength of the laser light 8 due to the use of a dielectric multilayer film or the like, and the X-ray generation laser light 2
Is highly permeable to. Therefore, the X-ray generating laser beam 2 is incident on the inside of the laser container 4 with almost no loss.

Next, the operation of this embodiment will be described.

The X-ray generation laser beam 2 generated by the X-ray generation laser device 1 is condensed by the condensing optical system 3, passes through the total reflection mirror 9 of the discharge excitation gas laser device 7, and is discharged. It is irradiated to 5. Since a peak light intensity of at least 10 ¹² W / cm ² or more is required to generate X-rays, the focusing optical system 3 needs to focus the laser light by using at least one mirror. is there. The number of mirrors required for the condensing mirror system depends on the beam profile of the X-ray generating laser beam 2, the divergence angle and the converging shape.

When the laser beam is focused linearly in accordance with the shape of the discharge electrode as shown in FIGS. 1 and 2, the focusing optical system 3 is preferably a cylindrical mirror.

As shown in FIG. 2, a part of the discharge electrode 5 is turned into plasma by the X-ray generating laser beam 2 linearly condensed by the cylindrical mirror 3 to generate X-rays. The X-rays ionize the laser gas in the space between the discharge electrodes 5 and 6 to generate electrons. The generated X-ray spectrum is
It contains a long wavelength component of 10 nm or longer and is composed of a narrow band spectrum due to band-band transition of electrons in plasma and a wide band spectrum due to free-band transition. ,
It is less likely to be absorbed by the laser gas and the utilization efficiency for ionization is low, and on the other hand, it is possible to suppress generation of short-wavelength X-rays that easily leak from the apparatus.

A high voltage power supply 11 synchronized with the preionization laser device 1 applies a high voltage between the discharge electrode 5 and the discharge electrode 6 to excite the laser gas in the laser container 4 to oscillate the laser light 8. .

In the above embodiments, the operating voltage of the laser device for X-ray generation was several hundred V when using the flash lamp pumped solid-state laser, and several V when the semiconductor laser pumped solid-state laser was used.

Further, in the above embodiments, the laser beam for X-ray generation is linearly focused on the discharge electrode 5 to realize uniform and efficient preionization. However, it is possible to generate X-rays without linearly focusing. In that case, the generation efficiency of X-rays can be improved by making the surface of the light collecting place uneven.

Further, it is possible to generate X-rays at any place other than the discharge electrode 5 in the laser container as the focus of the X-ray generating laser light.

In FIG. 1, the X-ray generating laser beam 2 is incident from the total reflection mirror 9 constituting the laser resonator, but the X-ray generating laser beam is incident on another place of the laser container 4. It is also possible to install a dedicated window. in this case,
The total reflection mirror 9 does not necessarily need to use a dielectric multilayer film mirror.

If a polarization mirror is used as the total reflection mirror 9, the polarization of the X-ray generating laser light 2 and the laser light 8 is changed, so that the X-ray generating laser light 2 is hardly lost inside the laser container. Can be incident on.

[0038]

As described above, the preionization apparatus for discharge-excited gas laser according to the present invention generates X-rays inside the gas laser container to preionize the gas that is the laser medium, so that the X-rays generated with high efficiency are produced. All is exposed to the gas without loss. Therefore, the gas can be efficiently pre-ionized. In addition, the spectrum of the generated X-ray contains a long wavelength component of 10 nm or more, and these are efficiently absorbed by the laser gas, so that the gas can be efficiently ionized. Therefore, the power consumption for generating X-rays can be reduced.

Since the operating voltage of the X-ray generating laser is low, the safety of the device is improved and a compact and inexpensive device can be realized.

Further, by adjusting the focusing power of the laser and selecting the material of the target, it is possible to suppress the generation of hard X-rays having high transparency, so that the safety against X-rays is improved, and it is possible to use a lead plate or the like. Since a shield is unnecessary, an inexpensive device can be realized.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is an enlarged view of an electrode portion for explaining generation of X-rays.

FIG. 3 is a diagram showing a conventional X-ray preionization discharge excited gas laser device. [Brief Description of Drawings] 1 X-ray generation laser device 2 X-ray generation laser light 3 Focusing optical system 4 Laser container 5, 6 Discharge electrode 7 Discharge excitation gas laser device 8 Laser light 9 Total reflection mirror 10 Output mirror 11 High-voltage power supply 12 Cathode 13 Target 14 X-ray 15 Discharge electrode also serving as X-ray window 16 Discharge electrode 17 Laser vessel 18 High voltage

Claims (4)

[Claims] 1. A discharge excitation gas laser device having an electrode therein, an X-ray generation laser device for pre-ionizing a laser gas medium of the discharge excitation gas laser device, and laser light generated from the X-ray generation laser device. An X-ray preionization discharge excitation gas laser device, which has an optical system for condensing the light into the discharge excitation gas laser device. 2. The optical system linearly focuses laser light generated from the X-ray generation laser device onto an electrode inside the discharge excitation gas laser device by the optical system. 1. An X-ray preionization discharge excited gas laser device according to 1. 3. The X-ray preionization according to claim 1, wherein an electrode portion inside the discharge excitation gas laser device, on which the laser light generated from the X-ray generation laser device is focused, is made uneven. Discharge excitation gas laser device. 4. A discharge excitation gas laser device having an electrode inside, an X-ray generation laser device for pre-ionizing a laser gas medium of the discharge excitation gas laser device, and laser light generated from the X-ray generation laser device. An X-ray preionization discharge excitation gas laser device having an optical system for condensing, and entering and condensing inside the discharge excitation gas laser device, the laser device for generating X-rays prior to excitation of the laser gas medium by discharge. By injecting and condensing the laser light generated in step (1) into the discharge excitation gas laser device by the optical system, X-rays are generated inside the discharge excitation gas laser device, and the laser gas medium is pre-ionized by the X-rays. A method of oscillating an X-ray preionization discharge excited gas laser device, which is characterized.