Simulation of energy transfer processes in laser scalpels

A mathematical model has been considered for the tips of laser scalpels. Simulation problems have been solved numerically.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 60, No. 6, pp. 1005–1010, June, 1991.     

High current, high energy proton beams accelerated by a sub-nanosecond laser

The sub-nanosecond laser system available at PALS facility in Prague has been used in order to produce MeV proton beams with typical current density approaching 1 A/cm² at few tens of centimeters from the target surface. In spite of the relatively long pulse duration (0.3 ns) and low intensity (∼10¹⁶ W/cm²), far away from the forefront laser facilities used for advanced proton beam acceleration in the recent years (from tens of femtoseconds to few picoseconds), the obtained results are promising both in terms of maximum proton energy and fast proton current. Real-time diagnostics systems, mainly in time-of-flight (TOF) configuration, have been used in order to estimate maximum and peak energy of the plasma fast proton component, peak current density, total number of fast protons and conversion efficiency of laser energy into accelerated fast proton total energy. Optimization of the maximum attainable proton energy and current has been carried out by irradiating targets of different composition as well as varying the laser energy and the focal spot diameter. Experimental results, as well as possible applications in material science and nuclear physics, are discussed and compared with literature data.     

Design of bipolar current source with amplitude up to 200 mA

One of the major requirements on the performance of a current source used for existing sensors is its amplitude stability. A method for designing a bipolar current source with amplitude up to 200 mA is developed. Its operating frequency is 10 kHz. The application of automatic control principles to the design of such a source makes the required amplitude stability possible. The circuit and its test data, including the maximum output amplitude, internal impedance, output regulation, and adjustment characteristic for an actual source, are given. This current source has successfully been used to excite the sensor of a continuous casting slag detector     

Preparation of a transparent alumina film doped with fluorescence dye and its energy transfer laser emission

A transparent alumina film was prepared from an aqueous sol by the sol-gel process. Changes in the fluorescence of 7-azaindole were monitored during the processing from the aqueous sol to the dried gel by dehydration. Coumarin 1, which is insoluble in water, and an anionic dye, uranin, were doped into the film by utilization of surface-active reagents, Triton X-100 and cetyltrimethylammonium bromide respectively. This doped film exhibited energy-transfer-type laser emission by nitrogen laser pumping.     

Spectral and laser studies on energy transfer binary dye-doped polymer laser rods

The energy transfer mechanism of two different dyes, C450 as donor and C535 as acceptor incorporated into polymeric matrices, is investigated. The absorption and fluorescence characteristics of C450 and C535 dye-doped polymer modified with ethanol are studied. The results are compared with their respective liquid mixtures. The spectral parameters of C450 and C535 in polymer and the corresponding monomer compositions are obtained. We study the variation of gain for different acceptor concentrations whilst keeping the donor concentration fixed. The gain of acceptor with donor increased and then decreased as the acceptor concentration was increased. Both solid and liquid media showed similar trends. We also study the photobleaching of the dye-doped polymer rod under nitrogen laser excitation.     

双极性膜内水迁移速度与最大电流密度间的关系

介绍了水向双极性膜中迁移的速度与膜的最大电流密度之间的关系。理论分析和初步实验说明水的迁移可以用溶解扩散机理来描述，为提高膜的最大电流密度必须提高膜对水的迁移能力。     

New improved bipolar and bilateral voltage to current converters

Some improved bipolar, bilateral voltage-source-to-current-signal converter schemes, using operational amplifiers (OA) as active devices, are described. Some of them are derived from an earlier scheme that uses the OAs in summing mode, and the others are derived from the conventional technique of using the OAs in current output configurations. Except for one scheme that uses a single OA for the realization, the others have ideal voltage-to-current transfer ratio and characteristics. The realization constraints in each case have considerable degrees of flexibility, and there is no effect of load variation as long as the OAs used in the schemes are not saturated due to increased input conditions. The admittance matrices, constraints of realizations, and sensitivity to passive parameters for the different schemes are tabulated for ready reference. It is shown that the schemes can be used as V-I and I-V converters with scaling facility of the conversion factors     

The application of a beam profile monitor as a beam current integrator for charged particle accelerators

A new procedure to obtain an online measurement of the beam intensity for charged particle accelerators, as well as the total charge deposited on a target, using a commercial beam profile monitor (BPM) is described in this paper. This procedure can be an alternative to the use of Faraday cups in experiments where their implementation is not feasible.     

Cellular signal transduction events as a function of linear energy transfer (LET)

In order to obtain a deeper insight into the molecular mechanism controlling the cellular response to high-linear energy transfer (LET) radiation, the number and size of pATM (S1981) and gamma-H2AX foci were compared in cultures of diploid human fibroblasts after exposure to charged particles of varying species, energy and LET at the NIRS-HIMAC-facility (Chiba, Japan). Particle LET ranged from 2.2 to 300 keV/mum, and a low fluence of 7.3 x 10(4) cm(-2) was chosen. Therefore, about 1 out of 7 nuclei was traversed by a particle. Doses and LET were verified with thermoluminescence detectors (LiF:Mg, Ti) evaluated according to the high temperature ratio method. Two hours after irradiation, fibroblasts were fixed and the subcellular distribution of pATM (S1981) and gamma-H2AX was visualised by immunofluorescence or histochemical staining using phosphorylation-specific antibodies. It was found that the number of pATM (S1981) foci per nucleus was higher after exposure to higher-LET particles. Irradiation with the two highest LET beams (Fe-ions, 197 and 300 keV/mum) gave a significant increase in the number of pATM foci, whereas ions with an LET lower than 30 keV/mum yielded similar numbers of pATM foci compared with unirradiated control samples. These data show that the early cellular response to high-LET radiation is modulated by the energy deposition of the particle. Therefore, the correlation between the microdosimetric aspect of energy deposition and biologic consequences at low radiation doses deserves further study.     

Thermal energy transfer by plasmon-resonant composite nanoparticles at pulse laser irradiation

Heating of composite plasmon-resonant nanoparticles (spherical gold nanoshells) under pulse laser illumination is considered. The numerical solution of the time-dependent heat conduction equation accounting for spatial inhomogeneities of absorbed laser radiation is performed. Important features of temperature kinetics and thermal flux inside nanoparticles are analyzed. Possible applications of the observed effects in nanotechnology and medicine are discussed.     

Analysis of an analog-digital converter with a dynamic integrator

Translated from Izmeritel'naya Tekhnika, No. 6, pp. 38–40, June, 1990.     

Optical transfer function design by use of a phase-only coherent transfer function

The design of a desired optical transfer function (OTF) is a common optical problem that has many possible applications. A well-known application for the OTF design is beam shaping for incoherent illumination. However, other applications, such as optical signal processing, can also be addressed with these systems. We derive a mathematical expression for an optimal phase-only filter that, when attached to an imaging lens, provides an optimal approximation in the sense of the minimal mean square error to the desired OTF function. Because of the fact that a phase-only filter is used, high efficiency is achieved.     

Development and application of programs to measure modulation transfer function, noise power spectrum and detective quantum efficiency

This project aimed to produce programs to calculate the modulation transfer function (MTF), noise power spectrum (NPS) and detective quantum efficiency (DQE) of digital X-ray systems, given a suitable digital image. The MTF was calculated using the edge technique and the NPS was calculated from a flat field image. Both programs require a suitably edited DICOM image as input. The DQE was then calculated from the output of MTF and NPS programs. This required data external to the DQE program to estimate the number of quanta per mm2 in the beam which formed the NPS image. All three programs run independent of each other on a PC and require no special software to be installed. Results for MTF, NPS and DQE for a Philips AC3 CR system are presented. In addition, the results for MTF from a Siemens Duo CT scanner with a specially designed PTFE edge are also shown.     

Enhancing the transfer of inductive energy to imploding plasma loads with a single-step meatgrinder circuit

The transfer of magnetic energy to an uncoupled load inductor using a novel inductive storage and transfer circuit (single-step meatgrinder) is compared with two classical inductive circuits. The first is the inductor-inductor transfer via an opening switch. The second is a transformer circuit where the primary circuit is opened and energy is transfered to the secondary and the uncoupled load. For identical loads the new circuit is shown to provide a 90-percent improvement over the two conventional circuits in energy transferred to the uncoupled load. A low-current low-voltage experiment, where 35.4 percent of the initial inductive energy is transferred to an uncoupled load using the new circuit, is discussed. A physical design for the Air Force Weapons Laboratory Shiva bank, which accounts for voltage holding, coupling, and parasitic inductance in the switches, is also described.