The Division at the Raja Ramanna Centre for Advanced Technology is engaged in a variety of R&D activities related to laser-plasma interaction with special emphasis on research relevant to laser driven Inertial Confinement Fusion, laser-plasma interaction at ultrahigh intensities, generation of high brightness thermal and coherent x-ray radiation and its applications, and investigations of equation of state of matter at extremely high pressures.

Research & Development Activities at Laser Plasma Division, RRCAT.

High Power Laser Systems

The Division has constructed a two beam Nd:Glass laser system (100 joule, 1 ns, 1.054 micron wavelength, each beam). Two more high power laser systems have also been set up and are being used for studies of laser plasma interaction in long and short pulse regimes. The first one is an Nd:phosphate glass laser chain whose output has been frequency up-converted to give 4J, 3 ns laser pulses at 0.53 micron. The second is a 100 GW, 25ps Nd:phosphate glass laser system given pulses at fundamental as well as at 0.53 micron (optionally). The 4J, 3ns laser was the work horse of the Division for many years since 1993 and this laser has now been decommissioned in January 2007.

A 1 TW Table Top Terawatt laser (Nd:glass) based on Chirped Pulse Amplification technique has been constructed and made operational. This is augmented with a 10 TW, 50 fs Ti:sapphire laser system to conduct investigations in the high field regime. Currently, studies on self-modulated laser wave field acceleration, generation of very high (multi meV) bremsstrahlung x-rays, generation of highly charged ions etc. are in progress. Experiments on fusion reactions in gas clusters and solid deuterated targets are also planned.

A variety of diagnostics and x-ray detection systems with high spatial (few microns) and temporal (few ps) resolutions have been developed. These include a high resolution on-line imaging crystal spectrograph, free-standing transmission grating XUV spectrograph, flat field grating XUV spectrograph, MCP-CCD based x-ray pinhole cameras, x-ray streak camera, S-1 optical streak camera, infra-red streak camera, laser focal spot monitor, K-edge spectrograph, x-ray bolometer, optical shear interferometer, ion analyzer, Faraday detectors, NaI(Tl) detector for gamma rays, magnetic spectrograph for electron energy measurements, X-ray CCD camera based crystal spectrographs for soft x-rays, neutron time of flight spectrograph etc.

In addition to these, several single shot auto-correlators for measuring pulse duration, pulse tilt and chirp in ultrashort laser pulses have also been developed.

Using above laser systems and diagnostics, experimental studies have been carried out on laser-plasma coupling, energy transport, x-ray conversion, laser induced ablation for hydrodynamic stability of ablatively accelerated targets, x-ray enhancement in laser produced plasma expanding in a background gas, shock wave propagation in thin foils, EOS measurements of variety of materials at high pressures, and generation of quasi-Planckian thermal x-ray radiation from laser heated gold hohlraum targets.

In addition to the above, the Division is engaged in studies of laser plasma interaction with particular emphasis on research related to generation, characterization and applications of XUV-soft x-ray radiation. Basic as well as applied aspects of x-ray emission from laser produced plasmas are being investigated. Thermal x-ray generation and its dependence on laser and target parameters such as opacity enhancement in mix-Z plasmas, x-ray intensity enhancement and anomalous intensity ratios of x-ray spectral lines in expanding plasmas of non-equilibrium ionization, higher harmonic generation from solid surfaces have been studied.

Recently, experiments have been performed on absorption and scattering in plasmas produced from gas cluster targets. Using the 10TW Ti:sa laser, experiments at ultrahigh intensities like self-modulated laser wave field acceleration of electrons, generation of very high (multi meV) bremsstrahlung x-rays, generation of highly charged ions/protons, laser-solid cluster interaction, high order harmonic generation etc. are also in progress

Some numerical simulations studies are also being carried out using one and two dimensional radiation hydro codes. These include investigation on x-ray spectra from planar slab targets and effect of target and laser parameters on x-ray emission properties, radiation transport in laser produced plasmas and laser induced shock wave propagation in single and multi-layer targets. Recently work is also initiated in setting up a 3D-PIC code, and theoretical aspects of laser plasma interaction at ultrahigh intensities.

The Division has also carried out a number of studies on applications of laser produced plasmas of technological interest. These include : characterization of x-ray source for contact imaging, x-ray microscopic imaging of biological cells and physical microstructures with a spatial resolution better than 200nm, developing stereoscopic x-ray imaging technique using twin laser produced plasmas, spectral distribution of keV x-ray yield from gold plasma, laser driven monochromatic x-ray point source of short-pulse duration in a diode configuration, generation of high current density electron pulses from laser driven ferroelectrics, laser driven vacuum discharge, and analysis of isotopic enhancement in laser plasma plumes.

Development of a pulsed power capillary discharge plasma system has been taken up with a view to use it as a gain medium for XUV lasing transitions and as a wave-guide for ultrashort laser pulse propagation for laser plasma based electron acceleration schemes. Towards this purpose work has been carried out on a 400 kV Marx generator, high voltage (40 kV) power supply for charging it, CuSOM₄ resistor based divider for voltage measurement and Rogowski coil for current measurement. Experiments are in progress to study lasing in argon plasma.

In order to meet long term requirement of large size, high damage threshold optical coatings for the high power Nd: glass laser, the Division has set up a facility for sol gel coatings. Sol gel optical anti reflection (AR) coatings have been deposited using a spin coater and silica sol, followed by ammonia hardening process. These coatings have been deposited on various optical components like lenses, blanks and Nd: glass rods.

• Laser Plasma Laboratory
  
• High Power Laser Optics Laboratory
  

• Publications of the Division
  
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