H C Pant
Articles written in Pramana – Journal of Physics
Volume 25 Issue 1 July 1985 pp 63-70 Plasma Physics
Experimental investigations on ablatively accelerated thin plastic foil targets irradiated by a 6J, 5 nsec Nd: glass laser pulse, were conducted using shadowgraphy technique. A 2 nsec, 0.53 µm probe pulse, derived from the main laser was used for recording the foil motion. It was observed that 6 µm plastic foils could be accelerated to a velocity of about 3 × 106 cm/sec for an incident laser intensity of 5 × 1013 W/cm2 and the corresponding ablation pressure was 0.4 Mbar. Ablation pressure (
Volume 27 Issue 3 September 1986 pp 435-441 Plasma Physics
An enhanced spatial smoothing of ablative motion of thin plastic foil targets coated with high atomic number ablators such as gold or aluminium, irradiated by a spatially modulated Nd: glass laser beam was observed. Optical shadowgraphy coupled with double foil technique was used to observe the laser-irradiated foil motion. Laser irradiance used for the experiments was in the range of 1011–1013 watts/cm2. A 60–80% enhancement in the smoothing was observed for a laser beam modulation (width 75–150 µm) at the target surface.
Volume 27 Issue 5 November 1986 pp 701-706 Plasma Physics
Hydrodynmaic efficiency of laser-irradiated thin aluminum and gold-coated aluminum targets was experimentally determined using a specially designed cone calorimeter. Velocity of the accelerated target and ablation pressure were also estimated from the experimental data. The laser irradiance range used in the experiments was between 1012 and 1013 watts/cm2. Experiments indicate that the fall in the hydrodynamic efficiency due to gold coating on aluminum target is about 12% at an irradiance of 8 × 1012 W/cm2.
Volume 30 Issue 6 June 1988 pp 549-555 Experimental Techniques And Instrumentation
A simple method for measuring laser-induced ablation pressure is described. The technique utilizes the well-known double foil concept. In the present experiment the impact times were estimated by monitoring the reflectivity of the impact foil rear. The measurements were performed using a glass laser (1·06 µm wavelength) in the 1011−1013 W/cm2 irradiance range. Experimental results showed good agreement with those obtained using other techniques as also those with the self-regulating ablation model prediction.
Volume 45 Issue 5 November 1995 pp 439-451
Emission characteristics of a single heterostructure GaAs diode laser are reported using a simple driver circuit. It provides a single picosecond time duration optical pulse, a pulse train or a broad optical pulse depending on the amplitude and time duration of the electrical pump pulse. Results show that relaxation oscillation frequency depends on the amplitude of pumping current pulse as well as on some inherent property of diode laser, which seems to be the level of impurity in lasing medium. Variation of relaxation oscillation frequency with amplitude of current pulse shows only the qualitative agreement with the reported theoretical predictions.
Volume 55 Issue 5-6 November 2000 pp 773-779 Laser Plasmas, Contributed Papers
This paper presents the dynamics as well as the stability of laser produced plasma expanding across the magnetic field. Observation of some high frequency fluctuations superimposed on ion saturation current along with structuring in the pin hole images of x-ray emitting plasma plume indicate the presence of instability in the plasma. Two type of slope in the variation of x-ray emission with laser intensity in the absence and presence of magnetic field shows appearance of different threshold intensity of laser corresponding to each magnetic field at which this instability or density fluctuation sets on. This instability has been identified as a large Larmor radius instability instead of classical Rayleigh-Taylor (R-T) instability.
Volume 55 Issue 5-6 November 2000 pp 781-787 Laser Plasmas, Contributed Papers
An intense laser radiation (1012 to 1011 W/cm−2) focused on the solid target creates a hot (≥1 keV) and dense plasma having high ionization state. The multiple charged ions with high current densities produced during laser matter interaction have potential application in accelerators as an ion source. This paper presents generation and detection of highly stripped titanium ions (Ti) in laser produced plasma. An Nd:glass laser (KAMETRON) delivering 50 J energy (λ=0.53 µm) in 2.5 ns was focused onto a titanium target to produce plasma. This plasma was allowed to drift across a space of ∼3 m through a diagnostic hole in the focusing mirror before ions are finally detected with the help of electrostatic ion analyzer. Maximum current density was detected for the charge states of +16 and +17 of Ti ions for laser intensity of ∼1011 W/cm−2.
Volume 55 Issue 5-6 November 2000 pp 789-795 Laser Plasmas, Contributed Papers
An investigation of x-ray emission from Cu plasma produced by 1.054 µm Nd:glass laser pulses of 5 ns duration, at 2 × 1012 − 2 × 1013 W cm−2 is reported. The x-ray emission has been studied as a function of target position with respect to the laser beam focus position. It has been observed that x-ray emissions from ns duration plasma show a volume effect similar to subnanosecond plasmas. Due to this effect the x-ray yield increases when target is moved away relative to the best focal plane of the laser beam. This result supports the theoretical model of Tallents and has also been testified independently using suitably modified theoretical model for our experimental conditions. While above result is in good agreement with similar experimental results obtained for sub-nanosecond laser produced plasmas, it differs from result claiming filamentation rather than pure geometrical effect leading to x-ray enhancement for ns plasmas.
Volume 55 Issue 5-6 November 2000 pp 797-802 Laser Plasmas, Contributed Papers
The x-ray emission from slab targets of copper irradiated by Nd:glass laser (1.054
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