“PPAS” X-RAY ABSORPTION SPECTROSCOPY IN LASER-PRODUCED ALUMINUM PLASMA

We have developed and successfully demonstrated the "point projection absorption spectroscopy (hereafter abbreviated to PPAS)" technique to record keV X-ray absorption spectra in the coronal region of laser produced aluminum plasma which provides spatial information in the corona. Absorption spectrum of the Al Ⅻ 1s²-1s2p resonant line for time delays up to 250, 500 and 750 ps after the peak of the incident laser pulse have been observed. Analysis of an absorption spectrum should allow a high spatial resolution (< 25μm) history of the absorbing ion population density to be determined. The 1-D hydro-code JB19 has been used to simulate the experiment and the predictions are compared to the observations. Such comparison can be useful in validating parts of the codes used for gain prediction on recombination X-ray laser transitions.     

Processes underlying the laser photochromic effect in colloidal plasmonic nanoparticle aggregates

We have studied the dynamic and static processes occurring in disordered multiparticle colloidal Ag aggregates with natural structure and affecting their plasmonic absorption spectra under pico-and nanosecond pulsed laser radiations, as well as the physical origin responsible for these processes. We have shown that depending on the duration of the laser pulse,the mechanisms of laser modification of such aggregates can be associated both with changes in the resonant properties of the particles due to their heating and melting(picosecond irradiation mode) and with the particle shifts in the resonant domains of the aggregates(nanosecond pulses) which depend on the wavelength, intensity, and polarization of the radiation.These mechanisms result in formation of a narrow dip in the plasmonic absorption spectrum of the aggregates near the laser radiation wavelength and affect the shape and position of the dip. The effect of polydispersity of nanoparticle aggregates on laser photochromic reaction has been studied.     

Mass distribution studies in the <Superscript>19</Superscript>F + <Superscript>197</Superscript>Au reaction

Mass distribution and evaporation residue measurements have been carried out in the reaction ¹⁹F + ¹⁹⁷Au using the recoil catcher technique followed by off-line γ-ray spectrometry. The random neck rupture model (RNRM) has been used to compute the variance of the mass distribution ( σ²_A) and the average kinetic energy ( ˉ) of the fission fragments for the present system. The results of model calculations have been found to be in good agreement with the experimental observations. Measured evaporation residue cross-sections have been compared with the statistical model calculations.     

Stabilization and Shift of Frequency in an External Cavity Diode Laser with Solenoid-Assisted Saturated Absorption

A simple method to realize both stabilization and shift of the frequency in an external cavity diode laser （ECDL） is reported. Due to the Zeeman effect, the saturated absorption spectrum of Rb atoms in a magnetic field is shifted. This shift can be used to detune the frequency of the ECDL, which is locked to the saturated absorption spectrum. The frequency shift amount can be controlled by changing the magnetic field for a specific polarization state of the laser beam. The advantages of this tunable frequency lock include low laser power requirement, without additional power loss, cheapness, and so on.     

Analysis of Ar line spectra from indirectly-driven implosion experiments on SGII facility

This paper reports on the indirectly-driven implosion experiments on SGII laser facility in which Ar emission spectrum from Ar-doped D-filled plastic capsule is recorded with the crystal spectrometer. Spectral features of Ar Heβ line and its associated satellites are analysed to extract the electron temperature and density of the implosion core. Non local thermal equilibrium (NLTE) collisional-radiative atomic kinetics and Strark broadening line shape are included in the present calculation. By comparing the calculated spectrum with the measured one, the core electron temperature and density are inferred to be 700 eV and 2.5×10²³ cm^-3 respectively. With these inferred values of electron temperature and density, neutron yield can be estimated to agree with the measured value in magnitude despite of the very simple model used for the estimation.     

ELLIPSOMETRIC SPECTRA OF CONDUCTING POLYANILINE

We report the ellipsometric spectrum studies on a new kind of conducting polymers, polyaniline. In the UV-visible range (1.4-4.8eV photon energy region) the absorption coef-ficient, the complex dielectric function and the refractive index of polyaniline as functions of photon energy are obtained. The spectra of nonconducting and fully conducting polyaniline have been analyzed and discussed. The experimental results show that the emeraldine base form of polyaniline has a large energy gap (E_g～3.6eV) and its absorption spectrum shows a broad exciton absorption peak centered at 2 eV. The absorption spectrum of emeraldine salt after protonation have four absorption peaks centered at 1.5, 1.83, 3.0 and 3.88eV. We also investigated the spectrum evolution of the samples from nonconducting (σ<10^-9Ω^-1·cm^-1) to conducting (σ≈10⁺¹Ω^-1·cm^-1) states, and give the dielectric function and the refractive index of the samples.     

Temperature dependence of line parameters of ~(12)C~(16)O_2 near 2.004 μm studied by tunable diode laser spectroscopy

The absorption spectrum of carbon dioxide at 2.004 μm has been recorded at sample temperatures between 218.0 K and room temperature, by using a high-resolution tunable diode laser absorption spectrometer(TDLAS) combined with a temperature controlled cryogenically cooled absorption cell. The self-, N~(2-), and air-broadening coefficients for nine transitions of ~(12)C~(16)O_2 belonging to the 20012←00001 band in the 4987 cm~(-1)–4998 cm~(-1) region have been measured at different temperatures. From these measurements, we have further determined the temperature dependence exponents of the pressure-broadening coefficients. To the best of our knowledge, the temperature dependence parameters of the collisional broadening coefficients are reported experimentally for the first time for these nine transitions. The measured halfwidth coefficients and the air temperature dependence exponents of these transitions are compared with the available values reported in the literature and HITRAN 2012 database. Agreements and discrepancies are also discussed.     

Review of theoretical gain-optimization studies in 10.6µm CO2-N2 gasdynamic lasers

A comprehensive theoretical analysis of optimization of gain in CO₂-N₂ gasdynamic laser employing wedge or conical or hyperbolic nozzles with either H₂O or He as the catalyst is presented. After a review of previous work, the usual governing equations for the steady inviscid quasi-one-dimensional flow in a supersonic nozzle of a gasdynamic laser are used to obtain similar solutions for the various flow quantities, which variables are subsequently used to optimize the small-signal gain on theP(20) line of the (001) → (100) transition of CO₂ at wavelength 10.6μm. The corresponding optimum values like reservoir pressure and temperature and nozzle area ratio also have been predicted and presented in the form of graphs. The analysis predicts that employing of 2D-wedge nozzle results in higher gain values and the CO₂-N₂-H₂O gasdynamic laser employing 2D-wedge nozzle is operationally the best laser system for which the optimum value as high as 3.1 m⁻¹ gain can be obtained.     

Mechanisms of mineral scaling in oil and geothermal wells studied in laboratory experiments by nuclear techniques

Two independent nuclear methods have been developed and tested for studies of mineral scaling mechanisms and kinetics related to the oil and geothermal industry. The first is a gamma transmission method to measure mass increase with a 30 MBq source of ¹³³Ba. The other method applies radioactive tracers of one or more of the scaling components. CaCO₃-precipitation has been used as an example here where the main tracer has been ⁴⁷Ca²⁺. While the transmission method is an indirect method, the latter is a direct method where the reactions of specific components may be studied. Both methods are on-line, continuous and non-destructive, and capable to study scaling of liquids with saturation ratios approaching the solubility product. A lower limit for detection of CaCO₃ with the transmission method in sand-packed columns with otherwise reasonable experimental parameters is estimated to be <1 mg in a 1 cm section of the tube packed with silica sand while the lower limit of detection for the tracer method with reasonable experimental parameters is estimated to <1 μg in the same tube section.     

Some new progress on the light absorption properties of linear alkyl benzene solvent

Linear alkyl benzene(LAB) will be used as the solvent in a liquid scintillator mixture for the JUNO antineutrino experiment. Its light absorption properties should therefore be understood prior to its effective use in the experiment. Attenuation length measurements at a light wavelength of 430 nm have been performed on samples of LAB prepared for the JUNO experiment. Inorganic impurities in LAB have also been studied for their possibilities of light absorption in our wavelength of interest. In view of a tentative plan by the JUNO collaboration to utilize neutron capture with hydrogen in the detector, we also present in this work a preliminary study on the carbon–hydrogen ratio and the attenuation length of the samples.     

ANALYSIS OF F′0+u ION-PAIR STATE OF IODINE

The optical-optical double resonant multiphoton ionization (OODR-MPI) technique and the fluorescent excitation spectroscopy technique have been applied to the study of the F′0⁺_u ion-pair state of iodine. This paper presents OODR-MPI spectrum and fluorescent excitation spectrum of I₂ in the region of 54000-55300cm^-1 by the three-photon resonant, two-photon ionization (1+2+2) and (1+(1+1)+2) processes.     

Charge state distribution analysis of Al and Pb ions from thelaser ion source at IMP

A prototype laser ion source that could demonstrate the possibility of producing intense pulsed high charge state ion beams has been established with a commercial Nd:YAG laser (E_max=3 J,1064 nm,8-10 ns) to produce laser plasma for the research of Laser Ion Source (LIS). At the laser ion source test bench,high purity (99.998%) aluminum and lead targets have been tested for laser plasma experiment. An Electrostatic Ion Analyzer (EIA) and Electron Multiply Tube (EMT) detector were used to analyze the charge state and energy distribution of the ions produced by the laser ion source. The maximum charge states of Al¹²⁺ and Pb⁷⁺ were achieved. The results will be presented and discussed in this paper.     

Generation of coherent tunable deep UV radiation for detection and absorption studies of explosives RDX and TNT

We report a technique for the efficient generation of tunable coherent deep UV radiation and its application in studies of RDX and TNT at the ppm level on the basis of their absorption characteristics. The obtained experimental absorption data are compared with conventional spectrophotometric data. The UV radiation in the range 200–260 nm has been generated by the type-I noncollinear third harmonic of the dye laser radiation (600–700 nm) and also by sum frequency mixing (SFM) of Nd:YAG output (1064 nm) with the second harmonic of the dye laser in β-barium borate (BBO) crystal. The maximum conversion efficiency of the generated signal is estimated to be 57.5% at λ = 218.9 nm wavelength. Apart from measurements of the absorbance of RDX and TNT at different concentrations in their respective solutions, the minimum detection concentrations have also been ascertained. The estimated minimum detectable concentration of RDX is 8.47·10⁻⁹ M, whereas that for TNT is 35.7·10⁻⁹ M. The data were obtained using only ∼100 μJ/pulse of laser energy. Published in Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 6, pp. 516–521, July–August, 2007.     

Q-Switching Pulse Generation with Thulium-Doped Fiber Saturable Absorber

Q-switched pulsed laser systems operating in the eye-safe wavelength region （λ〉 1.4 μm） are promis- ing for applications such as light detection and ranging （lidar）, differential absorption lidar, optical communi- cation, sensor and instrumentations. Fiber lasers are particularly attractive for such applications due to the fact that the beam quality can be independent of output power and they can be robustly engineered. There is an increasing interest in Q-switched erbium- doped fiber lasers （EDFLs）, which can be generated by using either active or passive techniques. Com- pared with the actively Q-switched ones, passively Q- switched EDFLs have attracted much attention for their advantages of compactness, low cost, flexibility and simplicity of design. Different kinds of saturable absorbers, such as the transition metal-doped crys- tals and semiconductor quantum-well structures, have been applied to realize Q-switched EDFLs.How- ever, when they are used in the laser cavity, additional alignment devices, such as lens, mirrors or U-bench units, have to be applied. This may increase the in- sertion loss and the complexity of the laser cavity.     

Development in Laser Induced Extrinsic Absorption Damage Mechanism of Dielectric Films

Absorption of host and the temperature-dependence of absorption coefficient have been considered in evaluating temperature distribution in films, when laser pulse irradiates on films. Absorption of dielectric materials experience three stages with the increase of temperature： multi-photon absorption; single photon absorption; metallic absorption. These different absorption mechanisms correspond to different band gap energies of materials, which will decrease when the temperature of materials increases. Evaluating results indicate that absorption of host increases rapidly when the laser pulse will be over. If absorption of host and the temperature-dependence of absorption are considered, the maximal temperatures in films will be increased by a factor of four.     

Dose estimation and shielding calculation for X-ray hazard at high intensity laser facilities

An ionizing radiation hazard produced from the interaction between high intensity lasers and solid targets has been observed. Laser-plasma interactions create "hot" electrons, which generate bremsstrahlung X-rays when they interact with ions in the target. However, up to now only limited studies have been conducted on this laser-induced radiological protection issue. In this paper, the physical process and characteristics of the interaction between high intensity lasers and solid targets are analyzed. The parameters of the radiation sources are discussed, including the energy conversion efficiency from laser to hot electrons, hot electron energy spectrum and electron temperature, and the bremsstrahlung X-ray energy spectrum produced by hot electrons. Based on this information, the X-ray dose generated with high-Z targets for laser intensities between 10¹⁴ and 10²⁰ W/cm² is estimated. The shielding effects of common shielding items such as the glass view port, aluminum chamber wall and concrete wall are also studied using the FLUKA Monte Carlo code. This study provides a reference for the dose estimation and the shielding design of high intensity laser facilities.     

Multilayer-based soft X-ray polarimeter at the Beijing Synchrotron Radiation Facility

A compact high precision eight-axis automatism and two-axis manual soft-ray polarimeter with a multilayer has been designed, constructed, and installed in 3W1B at the Beijing Synchrotron Radiation Facility (BSRF). Four operational modes in the same device, which are double-reflection, double-transmission, front-reflection-behind-transmission and front-transmission-behind-reflection, have been realized. It can be used for the polarization analysis of synchrotron radiation. It also can be used to characterize the polarization properties of the optical elements in the soft X-ray energy range. Some experiments with Mo/Si and Cr/C multilayers have been performed by using this polarimeter with good results obtained.     

Plasma sprayed alumina coatings for radiation detector development

Conventional design of radiation detectors uses sintered ceramic insulating modules. The major drawback of these ceramic components is their inherent brittleness. Ion chambers, in which these ceramic spacers are replaced by metallic components with plasma spray coated alumina, have been developed in our Research Centre. These components act as thin spacers that have good mechanical strength as well as high electrical insulation and replace alumina insulators with the same dimensions. As a result, the design of the beam loss monitor ion chamber for CAT could be simplified by coating the outer surface of the HT electrode with alumina. One of the chambers developed for isotope calibrator for brachytherapy gamma sources has its outer aluminium electrode (60 mm dia × 220 mm long) coated with 250 μ thick alumina (97%) + titania (3%). In view of potential applications in neutron-sensitive ion chambers used in reactor control instrumentation, studies were carried out on alumina 100 μ to 500 μ thick coatings on copper, aluminium and SS components. The electrical insulation varied from 10⁸ ohms to 10¹² ohms for coating thicknesses above 200 μ. The porosity in the coating resulted in some fall in electrical insulation due to moisture absorption. An improvement could be achieved by providing the ceramic surface with moisture-repellent silicone oil coating. Irradiation at Apsara reactor core location showed that the coating on aluminium was found to be unaffected after exposure to 10¹⁷ nvt fluence.     

A new Monte Carlo code for absorption simulation of laser-skin tissue interaction

In laser clinical applications,the process of photon absorption and thermal energy diffusion in the target tissue and its surrounding tissue during laser irradiation are crucial.Such information allows the selection of proper operating parameters such as laser power,and exposure time for optimal therapeutic.The Monte Carlo method is a useful tool for studying laser-tissue interaction and simulation of energy absorption in tissue during laser irradiation.We use the principles of this technique and write a new code with MATLAB 6.5,and then validate it against Monte Carlo multi layer (MCML) code.The new code is proved to be with good accuracy.It can be used to calculate the total power absorbed in the region of interest.This can be combined for heat modelling with other computerized programs.