Spectroscopy and Spectral Analysis of Soft X-ray Vacuum UV Spectral Sources Chen Bo, Ni Qiliang, Cao Jianlin, Li Futian, Chen Xingdan National Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, National Focus of Applied Optics.
In order to make the continuous spectrum radiation repetitive and stable, the argon arc works by flowing gas. The purity of the argon gas from the gas cylinder is 99.99%, and the purity reaches 99.999% after the gas purifier; then the shut-off valve, the trim valve, the flow meter and the pressure sensor enter the argon arc light source, the waste argon flows through the flow meter, trim valve, and stop valve And gas pump emissions.
As the gas is continuously updated, the content of air and water vapor impurities in the arc chamber and gas system is reduced, and the intensity of the impurity lines (such as oxygen, nitrogen, carbon, and hydrogen, etc.) emitted by the emission system is weakened. The pressure in the arc chamber is generally 0.1~2MPa, which is monitored by a pressure sensor and the accuracy is about 0.1%. When there is a differential pump unit, the argon inlet flow rate is 4.9Lmin-1, the outlet flow rate is 0.3Lmin, and the rest is discharged by the differential pump unit. When there is no differential pump unit, the outlet and inlet flow are 0.3L argon arc light source maximum operating current 40A, working voltage 53V, is supplied by high-precision DC steady current power supply, current stability is 0.02% * h-1. Source spectral radiation stability Sex and repeatability are better than *0. In order to obtain higher plasma temperature and electron density to generate black body spectrum lines, a 10kWf high-power wall stability argon arc light source has been specially developed in this research institute; it has also been developed to meet the general application of the laboratory. The popular 1kWf argon-arc light source; thus forming 1, 2.5 and 10kW "wall stabilized argon arc ultraviolet-vacuum ultraviolet light source series, suitable for a variety of different applications.
2 Soft X-rays Penning gas discharge light source 131 Soft X-rays Penning light sources consist of a cathode, an anode, and a permanent magnet 3, the structure of which is shown. The two cathodes are placed in a relatively uniform shape and size, and each includes a cylindrical cathode seat made of a copper alloy and a circular cover plate made of a high-permeability alloy, and a permanent magnet placed between the cathode seat and the cover plate. .
The cathode is fixed on the cathode seat and can be replaced. Cathode diameter 020mm, thickness 8mm, material is aluminum alloy or magnesium alloy. When the operating current is 500mA, the sputtering rate is 0.8mmh-1, so when working at a high current of 500mA, the cathode life is about 8~10h. The anode is in the form of a ring, two pieces in total, made of copper alloy, in the vertical A discharge channel with a diameter of 20 mm is formed in the straight direction. The use of high pressure magnetic material made of tight pressure bolt not only the cathode - anode - cathode tightly sealed, but also in the main discharge outside the closed magnetic circuit to prevent leakage. Tests show that when the magnet gap is 34mm, the discharge channel center magnetic induction intensity of up to 0. 1T. To prevent the cathode, anode, magnet overheating, the cathode and the anode water cooling, water flow is about 2LMmin-1. A DC steady current power supply, maximum voltage 2000V, maximum current 500mA, current stability better than * 0.5% Different from the usual gas discharge, Penning discharge in the discharge channel of the axial application of a strong uniform magnetic field. In this way, the electrons emitted from the cathode are confined by the magnetic field during the process of flying toward the anode, and the roller line moves under the combined action of the electric field and the magnetic field. The space orbit of the electrons is greatly lengthened, and the probability of impact ionization and collision excitation with gas molecules also increases accordingly. The positive ions formed by the discharge hit the cathode, forming a sputtering of the cathode material, and a higher-order ion spectrum of the working gas and the electrode material is generated in the plasma formed in the center of the discharge region. A soft X-ray-vacuum ultraviolet spectrum distribution map of aluminum electrodes for Penning light sources is given.
It can be seen that on the background of continuous radiation over 10 nm, a large number of strong high-order secondary ion lines appear depending on the working gas and the electrode material used.
Spectra were acquired by a McPherson 247 grazing incident vacuum-UV monochromator/photometer.
The light intensity stability of Penning light source is limited by the working pressure stability, electrode surface conditions and power supply stability. The test results show that the spectral radiation stability of Penning light source developed by the institute can reach 5% h-*RMS).
3 Dual Plasma Light Sources 41 The dual plasma light sources consist of three parts: a hot cathode, a barrier electrode, and an anode. The structure is as shown. Three axially magnetized ring-shaped barium ferrites are used to generate a magnetic field, and the surface magnetic induction intensity is about 0.1 T. The magnetic current is emitted from a magnetic pole. After the front flange and the diaphragm are fastened, the magnetic gap passes through the baffle plate. The plate and rear fastening flange return to the other pole. In order to ensure that the magnetic current between the baffle plate electrode and the diaphragm body is relatively concentrated, the diaphragm body, the front fastening flange, the baffle plate electrode and the rear fastening flange are all made of pure iron with good magnetic permeability. Using the oxide filament as the cathode, the filament current is 25A, heated by the DC steady current power supply, and the current stability is better than 0. The filament is activated before use to improve the electron emission efficiency. Discharge current of 3 ~ 5A, also by the DC steady current power supply through the voltage divider resistor. The current stability is better than 0.05% 'h-, the voltage drop between cathode and anode is about 40~50V. The light source is water-cooled and the water flow is 2 bumin-1. The argon or helium working gas with 99.99% purity is fine-tuned in two stages. After the valve is depressurized, it enters the light source and the working pressure is about 4-20 Pa. The double plasma light source applies both mechanical constraints and magnetic field constraints. The electrons emitted from the hot cathode ionize the working gas under the action of an electric field and form a free plasma without any constraints between the hot cathode and the baffle electrode. At the same time, another portion of the electron that has not been heated continues to move toward the anode and is pinched by the sudden decrease in aperture of the baffle electrode.
The spectra and ion spectra of the double plasma light source taken with a vacuum ultraviolet dry plate were given. The shortest observed wavelength is that the Hell test was performed on a McPherson 247 grazing vacuum UV spectrophotometer/monochromator.
The spectral radiation stability of the double plasma light source is affected by the operating pressure, discharge current, and geometry. Tests show that the spectral radiation stability of the dual plasma light source we developed is better than 3%. h-, 4 vacuum ultraviolet hollow cathode light source 151 vacuum ultraviolet hollow cathode light source consists of hollow cathode, cylindrical anode, light source chamber and differential pump unit 4 part Composition, structure as shown. In order to ensure long-term stable operation of the light source under large currents, the empty cathode of the light source has the following features in design and process: a hollow cathode made of a copper-tungsten alloy with a very low sputtering rate and excellent processability; a reasonable structure is selected and the cathode is ensured The largest effective area is used; the cathode base is made of a material with good thermal conductivity, and the water cooling will not cause the cathode working temperature to be too high.
Shields prevent lateral direct discharge between cathode and anode. Aluminium anodes are tapered and have a diameter of 60mm and are water cooled. The working pressure of the light source is about 10Pa. It is connected to the vacuum ultraviolet spectrometer system with a vacuum degree of 10-4Pa. The light source is equipped with a differential pump unit. When the light pressure in the light source is 10Pa, the vacuum degree of the measuring system can be guaranteed. The vacuum light source of the empty cathode is given. Photoelectric recording spectrum diagram. In the discharge current 380mA, voltage 1 500V, argon pressure 10Pa. Aril and other atomic and ion spectra can be obtained. Using H-Ne mixed gas, current 400mA, voltage 1500V, pressure 40Pa can be Hell30l4nm and Hel58.4nm atomic lines, and Hell30.4nm stronger than Hel58.4nm. The shortest wavelength measured by photoelectric recording is the Hell 25.6 nm ion wire.
The spectral radiation stability of the empty cathode light source is related to the empty cathode surface roughness, working air pressure, and current stability. The measured results show that the spectral stability of the empty cathode light source can reach *1%. h-, 5 laser plasma light source 16, 71 laser plasma (LPP) light source is focused high energy short pulse laser beam to generate high temperature plasma on the target The plasma produces soft X-ray radiation during the compounding process. The early common LPP light source is a metal or non-metallic target LPP light source composed of high-atomic-number materials. The LPP light source has high laser-soft X-ray conversion efficiency, good spectral radiation stability, and continuous radiation spectrum. However, this type of light source sputtering is extremely serious and is not suitable for use in strict environmental requirements and long-term continuous work. This research institute has developed the light source. In order to limit or completely eliminate the pollution of LPP light source sputtering, based on the research of metal target LPP light source, the key technology of frozen target, gas target and droplet target LPP light source frozen target light source is the formation of pollution-free freezing target. For this purpose, we use C2 gas at normal temperature as a working substance and freeze it under vacuum to a solid target. This frozen target LPP light source generates plasma and the sputtered debris quickly evaporates without causing damage to nearby optical components. Big damage. The formation of a solid C2 target utilizes a cryogenic gas deposition technique that first creates a locally low temperature gas deposition surface in the vacuum target chamber, and then introduces the frozen gas when the temperature of the gas deposition surface is lower than the critical temperature at which the frozen gas is condensed into a solid state. At this point, the gas will deposit on the low temperature surface and become solid. The design of our gas-freezing target light source is shown below.
In addition, we also developed a jet target laser plasma light source, which emits a high-pressure working gas from a rapid pulse jet valve into a vacuum target chamber, and generates high-pressure clusters in a local area near the nozzle in a vacuum state; At the same time, the high-energy pulsed laser light is focused on the jet target and generates a high-temperature plasma.
This light source can produce both soft X-ray radiation and eliminate the contamination of the optical elements near the plasma due to the scattering of solid target debris. However, the gas density of this target directly affects the radiance of the LPP light source, and its radiation brightness is far from the solid target. Therefore, the light source can only be used by some research institutes that do not require high brightness of the light source. The working principle of the light source is shown in FIG.
In the vacuum target chamber, a cold head with good heat conduction is inserted. The cold head is provided with a low-temperature gas deposition surface. The cold head is connected to a cold source equipped with liquid nitrogen outside the vacuum target. The amount of CO2 gas entering the vacuum target chamber is controlled by a high-vacuum needle valve, and the capillary conduit leads to the vicinity of the cryogenic surface, and a tiny solid C2 target can be formed on the low-temperature deposition surface. by. A liquid nitrogen constant temperature refrigeration unit is added outside the gas nozzle, the temperature control range is -77~473K, and the control precision is 0.2K. When the gas passes through the low temperature area, tiny droplets are formed. The tiny droplets are injected under the pressure of high pressure gas. Vacuum target room. At the same time, the laser is triggered to work, and the intense laser beam is focused on the droplet target to generate a high-temperature plasma. The density of the droplets of the micro-liquid is much higher than the density of the gas, so that soft X-ray radiation of higher intensity can be generated. 2 is the soft X-ray spectral distribution produced by the Xe and Kr targets. The experimentally measured laser-soft X-ray conversion efficiency at 13 nm is 0.75%/2 sr/2% bandwidth, and the working gas can be continuously supplied outside the vacuum target to ensure long-term stable operation of the light source.
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