Paramita Deb

A study of the penetration of electrons in compounds by Monte Carlo calculations

Describes Monte Carlo calculations pertaining to the penetration of electron beams through compounds. The distribution of the range of electrons in solids has been studied quantitatively. New data are presented on the reflection, absorption and transmission coefficients, the most probable range and the range distribution of electrons in a few typical compounds, for incident beam energies up to 0.5 MeV.

Determining the mean size and density of clusters, formed in super sonic jets, by Rayleigh scattering and Mach-Zehnder interferometer

In this work, the formation of clusters in a supersonic jet expansion has been investigated. Clusters of argon, carbon-dioxide, nitrogen, and oxygen have been generated in the gas jet with three different types of nozzles (0.5 mm diameter, 0.8 mm diameter, and a conical nozzle with 0.8 mm diameter aperture). The mean size and density of the clusters have been measured as a function of backing pressure. Here, density of clusters refers to the density of the cluster collection. Rayleigh scattering experimental data and Mach-Zehnder interferometer data have been combined to estimate the average size and density of clusters. CO2 and Ar clusters form easily at about a backing pressure of 2 bars, while N2 and O2 clusters do not form easily. N2 and O2 begin to cluster at a backing pressure of about 18–24 bars. The mean cluster radius of Ar varies from 6.6 A to 24 A and the cluster radius of CO2 varies from about 8.8 A to 35 A as the backing pressure increases from 3 bars to 14 bars. In the same range of backing ...

Nd:glass regenerative amplifier with increased bandwidth and high output energy for chirped pulse amplification systems

We demonstrate a large energy output and a wider output spectral bandwidth from Nd:glass-based regenerative amplifiers. The maximum energy extracted from the regenerative amplifier is 24 mJ with an overall gain of 3.4 x 10(8). The maximum output bandwidth achieved is 4.2 nm FWHM when the input pulse spectral bandwidth is 7 nm FWHM. This was made possible by a new cavity optimization technique.

Enhanced Bandwidth and Increased Energy from an Nd:Glass Regenerative Amplifier

A large energy output and a wider spectral bandwidth , not reported earlier from Nd:glass based regenerative amplifiers, is demonstrated. The energy extracted from the regenerative amplifier is 15 mJ, with a bandwidth of 3.8 nm aid an overall gain of 2.1X108. This is achieved by a new cavity optimization technique.

Induced birefringence in optically isotropic glass by a short pulsed Nd:YAG laser

We have observed laser induced birefringence in optically isotropic glasses as well as in Nd:YAG crystal using polarized pulses of wavelength 1.06 µm and duration 100 ps with an intensity near 109 W cm−2. The laser used in the experiment was a Nd:YAG oscillator–amplifier system. The change in the material induced by the laser was not a permanent change but existed for as long as the laser pulse lasted. We observed conoscopic patterns when the laser was passed through glass or the Nd:YAG crystal. These patterns are typically seen when light is passed through birefringent materials kept between a polarizer and analyser. This observation immediately suggests that the glass or the crystal possesses optical birefringence. This birefringence is demonstrated in fused silica glass, Nd:glass and Nd:YAG crystal. The circular symmetric conoscopic patterns show that the optic axis is formed along the direction of laser propagation. The laser induced birefringence depended on the laser intensity and we characterized the magnitude of this change by measuring the output pulse at the end of the crossed polarizer.

The study of deep levels in InSb and HgCdTe by transient gratings at two photon excitation

Transient grating measurements on n-InSb and n-HgCdTe are described. A simple yet sensitive technique has been devised, that locates the deep levels within the forbidden gap with an accuracy of about 0.2 meV. The results are in agreement with the results of other techniques and provides a direct method of detecting the presence of impurities or defects.

A model for short pulse absorption in a real SF6 saturable absorber

This paper describes a rate equation model that has been formulated for an SF6 saturable absorber. The model includes three transitions in the ν3 ladder and one hot band transition along with intramolecular V-V relaxation to the bath states. The coupled differential equations were solved using the Runge-Kutta method. The transmission characteristics have been calculated for several combinations of pulse length, cell length and SF6 pressure. Theoretical values of transmission are compared with the experimental data of Haglund et al., Taylor et al. and Daido et al., and it is found that the model explains the absorption behaviour more closely.

Temporal response of a SF6 saturable absorber to short pulses of CO2 laser at 10.6μm

Abstract This paper reports the temporal change in the absorption of SF6 when it interacts with short pulses of 10,6 μm radiation at 300°K. A novel pump-probe technique, using a train of pulses of the P(20) line, where each pulse acts as a probe for the previous pump pulse, was employed for the study. It was found, surprisingly, that the absorption increases when it is pumped by a single short pulse (5 ns FWHM and fluence varying from 0.02 mJ cm 2 to 0.4 mJ cm 2 ) but decreases when pumped by two such pulses. The extent of this change also depends on the time delay between the pulses. This experiment also gives an insight into the V-V relaxation rates of levels below 1000cm−1.