Soft X-ray optimization studies on a dense plasma focus device operated in neon and argon in repetitive mode

This paper investigates the emission characteristics of a high-performance low-energy (3-kJ) repetitive dense plasma focus device, NX2, operated at up to 1-Hz repetition rate to develop it as an intense source of soft X-rays (SXR) for microlithography and micromachining. Various SXR yield optimization studies with argon and neon as filling gases were performed under different operating conditions (charging voltage, filling pressure, anode length, and insulator sleeve length). The SXR yield was computed using signals obtained from a PIN diode SXR spectrometer with appropriate filters. When operated in neon, the average optimum SXR (/spl lambda//spl sim/1 nm) yield in 4/spl pi/ steradians was found to be up to 140 J/shot, which corresponded to a wall plug efficiency of 5.6%. Operation in argon showed that optimized SXR (/spl lambda//spl sim/0.4 nm) yield was up to 1.3 J/shot. While operating with neon under optimized conditions with a water-cooled anode in repetitive mode, the NX2 device was used as a SXR source to imprint a test lithograph on a highly sensitive chemically-amplified resist SU-8. Test structures showing the effect of a stepper with aspect ratio 3:1 on 10-/spl mu/m-thick SU-8 resist film were obtained.     

Study of molybdenum K-series line radiation emission from a low energy plasma focus

K-series line radiation emission of Mo and Cu from a low energy Mather-type plasma focus is investigated. Quantrad Si pin diodes are employed as time resolved X-ray detectors, where as a pin hole camera is used for time integrated analysis. The measurable X-ray flux for hydrogen is observed in the pressure range of 0.5–3.5 mbar. Mo and Cu K-line radiation emission in this geometry has the highest values of about 0.05 J/sr and 0.17 J/sr, respectively at a filling pressure of 2.0 mbar. The corresponding efficiencies are 0.03% and 0.09%, respectively. Total X-ray emission and efficiency in 4π-geometry are also obtained with values 4.12 J and 0.18% at 2.0 mbar. The Mo K-line radiation emission may result due to interaction of energetic electron beam emitted from the focus region with the molybdenum insert.     

Enhancement of X-ray emission in the side on direction in a Mather-type plasma focus

A 1.8 kJ Mather-type plasma focus (PF) for argon and hydrogen filling is examined. Two anode configurations are used. One is tapered towards the anode face, and the other is cylindrical but the face is cut at different angles. At optimum conditions, the system is found to emit Cu–Kα X-rays of about 1.6±0.1 J/sr in the side-on direction for argon filling, which is about 32% of the total X-ray emission. In 4π-geometry, maximum total X-ray yield and wall plug efficiency found are 26.4±1.3 J and 1.5± 0.1% respectively. The modified geometry may help to use the PF as a radiation source for X-ray diffraction.     

Comments on "On asymptotic matching and the sheath Edge"

In Sternberg and Godyak (2003), the authors claim that the sheath edge obtained through asymptotic matching is the edge of the electron free ion sheath characterized by Godyak's "strong" electric field |E|=kT/sub e//(e/spl lambda//sub D/). I present a careful re-analysis of the same problem and show that the paper is incorrect. The "intermediate region" of asymptotic analysis has an extremely narrow validity range in potential space and does not contain the ion-electron sheath. Consequently, in asymptotic theory, the sheath edge is uniquely defined by the transition from the quasi-neutral plasma to the ion-electron sheath. It may equivalently be characterized by the Bohm criterion or by a "medium" electric field |E|/spl sim/kT/sub e//(eL/sup 3/5//spl lambda//sub D//sup 2/5/) mediating between strong sheath fields |E|/spl sim/kT/sub e//(e/spl lambda//sub D/) and weak plasma fields |E|/spl sim/kT/sub e//(eL).     

Correlation of plasma electron temperature with neutron emission ina low-energy plasma focus

Correlation of neutron emission with plasma electron temperature in a low-energy (2.3 kJ) plasma focus is investigated. To determine the plasma temperature by continuum X-ray analysis, cobalt is selected as the filter, which discriminates the line radiation from the background impurities like carbon, nitrogen, and oxygen, or the copper of which plasma focus electrodes are made. For a pressure range of high neutron emission (1-4 mbar), the neutron yield is found to correlate with the plasma temperature. The highest temperature recorded is 5 keV at 2.5 mbar, the filling pressure for the highest neutron emission in this device     

激光诱导氩气等离子体时间分辨特性研究

激光诱导击穿光谱(L IB S)以激光诱导微等离子体的原子发射为技术特征,在科研与工业领域正得到重视与蓬勃发展.作为环境气体的氩气对等离子体演化过程中粒子的碰撞过程有重要影响,决定着L IBS技术分析性能的发挥.利用光谱诊断技术深入研究LIBS技术条件下氩气的光谱特征,对于提升LIBS技术及其应用水平具有重要的意义.利...     

Second-harmonic generation of a Gaussian laser beam in a self created magnetized plasma channel

The second-harmonic generation of an intense self-guided right circularly polarized laser beam in a magnetized plasma is investigated. The laser imparts oscillatory velocity to electrons and exerts a radial ponderomotive force on them to create a depleted density channel. The critical power for self-focusing shows huge reduction as electron cyclotron frequency approaches the laser frequency (/spl omega//sub c/ /spl rarr/ /spl omega/). In the presence of the self-created radial density gradient, the laser drives a density perturbation at the fundamental frequency. The density perturbation beats with the oscillatory velocity to produce a second harmonic current density, driving second harmonic radiation copropagating with the laser. The second harmonic, however, is azimuthally asymmetric with /spl theta/-variation as exp(i/spl theta/). Its amplitude shows resonant enhancement as /spl omega//sub c/ /spl rarr/ /spl omega/.     

Two-Photon Laser-Induced Fluorescence Spectra of Argon in a Grimm-Style Glow Discharge Tube

Two-photon excited laser-induced fluorescence (LIF) spectra of argon atom were successfully observed in a Grimm-style glow discharge tube, which has widely been applied to depth profiling of the elemental composition on various film-like samples by emission spectrometry. The LIF signal of an argon atomic line at 641.63 nm was observed when the glow discharge argon plasma was illuminated by a pulsed Ti:sapphire laser radiation of 7–10 mJ/pulse at 753.39 or 795.66 nm without focusing of the laser beam.     

Accelerating voltage and electron temperature in a FXR discharge

X-ray quantum energies as well as electron temperatures in different parts of the discharge column in a flash X-ray (FXR) discharge have been estimated. It is found that the energy of the X-radiation is about 16 keV very near the cathode surface and about 30 keV at the anode during the first pinching of the discharge column (Initial voltage 20 kV). The electron temperature in the column is found to be 2 to 2.5 keV during the pinch interval, thereafter it rapidly decreases. A dark space is localized to a region just outside the anode surface. This dark region follows the anode when the inter-electrode spacing is varied.     

Industrial-scale experiments of desulfuration of coal flue gas using a pulsed corona discharge plasma

The flow rate of flue gas in the industrial experiments was 3000 Nm/sup 3//h. The flue gas from the boiler burning coal was used. The influences of operating parameters on the efficiency of desulfuration (DeSO/sub 2/) were studied, which include the retention period of flue gas in the reactor, the initial concentration of SO/sub 2/ in flue gas, a mole ratio of NH/sub 3/ to SO/sub 2/ in the gas, the temperature of the gas, as well as the power consumption of pulsed corona discharges. The experimental results shown that the efficiency of DeSO/sub 2/ was above 80%, when the initial concentration of SO/sub 2/ was 1000 /spl sim/ 2000 ppm, the gas temperature was 60 /spl deg/C /spl sim/ 75 /spl deg/C, the retention period was more than 5.8 s, a mole ratio of NH/sub 3/ to SO/sub 2/ was 2 : 1, the water content in flue gas was above 6%, and he consumption was 2.5 /spl sim/ 3.5 Wh/Nm/sup 3/.     

The new PIXE‐alpha spectrometer for the analysis of Roman nummi surfaces

The particle‐induced X‐ray emission (PIXE)‐alpha portable spectrometer of the Laboratori Nazionali del Sud has been upgraded to improve X‐ray energy resolution and efficiency. A value of 124 eV at Mn Κα‐line and a factor of 3 were, respectively, achieved. These enhanced capabilities allowed the thin surface examination of 5 Roman nummi, in which previous near‐surface X‐ray fluorescence measurements revealed traces of mercury. In particular, the new version of the PIXE‐alpha spectrometer has allowed the distinction of the 2.19 keV Hg M‐line from the 2.30 keV S K‐line and the 2.34 keV Pb M‐line. Subsequent elemental association has demonstrated a correlation between surface mercury and silver. Copyright © 2012 John Wiley & Sons, Ltd.     

Generation of broadly tunable picosecond mid-infrared laser and sensitive detection of a mid-infrared signal by parametric frequency up-conversion in MgO:LiNbO₃ optical parametric amplifiers

Picosecond optical parametric generation and amplification in the near-infrared region within 1.361-1.656 μm and the mid-infrared region within 2.976-4.875 μm is constructed on the basis of bulk MgO:LiNbO 3 crystals pumped at 1.064 μm.The maximum pulse energy reaches 1.3 mJ at 1.464 μm and 0.47 mJ at 3.894 μm,corresponding to a pumpto-idler photon conversion efficiency of 25%.By seeding the hard-to-measure mid-infrared radiation as the idler in the optical parametric amplification and measuring the amplified and frequency up-converted signal in the near-infrared or even visible region,one can measure very week mid-infrared radiation with ordinary detectors,which are insensitive to mid-infrared radiation,with a very high gain.A maximum gain factor of about 7 × 10 7 is achieved at the mid-infrared wavelength of 3.374 μm and the corresponding energy detection limit is as low as about 390 aJ per pulse.     

Doppler spectroscopy of hydrogen and deuterium Balmer alpha line in an abnormal glow discharge

The results of hydrogen and deuterium Balmer alpha line shapes and line intensities study in an abnormal glow discharge are reported and analyzed. The Doppler shifts along line wings are used to determine energies of excited hydrogen and deuterium atoms. For 12 different cathodes, intensity and shape of line wings are examined and dependence upon cathode material is determined. Tentative explanation of line wings intensity dependence is related to the sputtering of cathode material and back-scattering coefficients of incident hydrogen or deuterium ions and atoms from cathode surface. The influence of the light reflected on a cathode surface to the line shape measurements along discharge axis is considered. In hydrogen, deuterium, and Ar+3%H/sub 2/ discharges, basic mechanisms of fast hydrogen generation and excitation are studied. The shape and intensities of the H/sub /spl alpha// line profiles in pure hydrogen and in argon-hydrogen mixture may be correlated with hydrogen atom-carrier gas collision excitation cross sections. In order to assess the importance of reflected fast hydrogen atoms back scattered from the cathode surface, for the Balmer line shape formation, a simulation program is used. The results are in a qualitative agreement with Balmer line shapes observations.     

Spectral distribution of radiation from the cascade arc plasma

A mathematical model has been developed for radiation emission and absorption in the cascade arc plasma, and calculations have been performed to determine the complete spectral distribution of radiation emerging from the argon arc. Although self-absorption effects are negligible for the continuum radiation, they are significant for much of the line radiation. The radiation flux emerging from the arc, as well as the efficiency for conversion from electrical to radiant energy, increase with increasing arc current and pressure and decreasing arc radius. The relative contribution of line radiation to the total arc radiation decreases with increasing current and pressure and decreasing radius.     

Amplified spontaneous emission of F2− color center in LiF crystal

Intense, directional, and narrow-bandwidth 1130-nm emission was generated from LiF crystal at room temperature by the pumping with radiation in the wavelength region of the absorption band of the F₂ ⁻ color center. The emission was observed by the pumping with radiation of pulse energy above 5 mJ, and the divergence angle of the beam was about 16 mrad. This emission is attributed to the amplified spontaneous emission by the F₂ ⁻ center. Received: 8 April 1999 / Revised version: 18 May 1999 / Published online: 16 September 1999     

Effects of type of radiation on glow curve and thermoluminescence emission spectrum of CaF2:Tm

Thermoluminescence emission spectra of CaF₂:Tm (TLD-300) samples irradiated with 48 keV X-rays ⁶⁰Co gamma rays, 4.5 MeV alpha particles and 15 MeV neutrons were measured in the 300–650 K temperature region. Seven emission bands were observed of which the one in the infrared (at 803 nm) is very intense. The emission bands can be assigned to ¹D, ¹G, ³F and ³H levels characteristic for Tm³⁺ de-excitation in a cubic field. All observed lines in the spectrum are due to 4f-4f transitions. The spectra undergo remarkable changes in intensity when the temperature is raised from room temperature up to 350°C, while the number of the emission bands remains constant. The glow curve structure is both dependent on emission wavelength and the type of radiation. Evidence has been found that the trapping structures responsible for glow peaks 2 and 3 alter under the influence of high LET () radiation. For glow peaks 4–6 the filling of the traps alters with the type of radiation. The observations can be explained assuming a TL process involving several hole trapping centres but with only one luminescent centre (Tm³⁺) active at all temperatures.     

Three Dimensional Angular Distributions of X‐Rays in a 4 kJ Plasma Focus Device for Different Anode Tips Using TLD‐100 Dosimeters

Time and energy integrated measurements of the 3‐D angular distribution of X‐rays emission within the chamber of a 4 kJ Mather‐type plasma focus is investigated employing four different anode shapes and using nitrogen as the filling gas by the TLD‐100 thermoluminescence dosimeters. The distributions of X‐ray radiation in the energy range of 5 keV to several hundred keV were bimodal for all of the anode tips, peaked approximately at ±15°. The intensity of X‐rays decreased abruptly along the central axis of the device where the quasi cylindrical plasma pinch was formed. High intensity of X‐ray was observed in the case of a tapered ?at‐end anode, whereas less was obtained with the cylindrical hollow‐end anode. The maximum nitrogen X‐rays were for the tapered flat‐end anode at 4.5 mbar and 13 kV. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

高能氩离子在聚苯乙烯中的电子能损效应研究

用1.4GeV氢离子对多层堆叠的厚约53m的聚苯乙烯薄膜在室温和真空条件下进行了辐照;对辐照后的样品进行了从红外到紫外的光吸收测量.测量结果显示,材料经高能红离子辐照后发生化学降解,降解过程强烈依赖于电子能损;在能量沉积密度很高的径迹芯中,分子主链和苯环均遭到破坏;在电子能损高于0.77keV/nm时有炔基产生.     

The accuracy improvement of the correlation factor erg/cm2R for low-energy X-radiation

In this paper the results of calorimetric measurements of the correlation factor erg/cm² R for filtered and unfiltered X-radiation in the energy region up to 220 keV are given. The value of the correlation factor for X-radiation filtered by 3 mm Cu measured by a calorimeter is compared with the values of the correlation factor calculated by an independent method from the energy spectra of the same radiation. The initial spectra are obtained by means of a numerical graphical method from transmission curves measured by means of an ionization chamber in copper and tin.This comparison has shown very good agreement between the calorimetric value of the correlation factor 3·-45. 10³ erg/cm² R and those calculated by using White's values of the correlation factor depending on the X-radiation energy, provided the average energy required to produce an ion pair in air is 34·0 eV. The experimental results thus obtained enable us also to evaluate the amount of average effective energy of the measured X-radiation which is equivalent to the energy of monochromatic X-radiation having the same correlation factor, in comparison with the effective energy, currently determined by ionization measurements of the half-value layers.The paper is dedicated to Professor F.Bhounek, Member of the Czechoslovak Academy of Sciences, on his 70th anniversary.The authors wish to thank the head of the Laboratory, Academician F. Bhounek, for allround attention to this work, Ing. V. Boková for valuable aid in the theoretical considertions and calculations, and J. Homola for setting up and performing the experiments.     

Generation of broadly tunable picosecond mid-infrared laser and sensitive detection of a mid-infrared signal by parametric frequency up-conversion in MgO:LiNbO3 optical parametric amplifiers

Picosecond optical parametric generation and amplification in the near-infrared region within 1.361-1.656 μm and the mid-infrared region within 2.976-4.875 μm is constructed on the basis of bulk MgO：LiNbO 3 crystals pumped at 1.064 μm.The maximum pulse energy reaches 1.3 mJ at 1.464 μm and 0.47 mJ at 3.894 μm,corresponding to a pumpto-idler photon conversion efficiency of 25%.By seeding the hard-to-measure mid-infrared radiation as the idler in the optical parametric amplification and measuring the amplified and frequency up-converted signal in the near-infrared or even visible region,one can measure very week mid-infrared radiation with ordinary detectors,which are insensitive to mid-infrared radiation,with a very high gain.A maximum gain factor of about 7 脳 10 7 is achieved at the mid-infrared wavelength of 3.374 μm and the corresponding energy detection limit is as low as about 390 aJ per pulse.