Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.486537
Title: High gain ultra-short laser pulse raman amplification in plasma
Author: Lyachev, Andrey
ISNI:       0000 0001 3614 2754
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2007
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Abstract:
This thesis presents an experimental study of broad-band Raman chirped pulse amplification in plasma. Amplification. of a short seed pulse occurs through stimulated Raman backscattering in the presence ofa counter-propagating chirped pump pulse in a preformed plasma waveguide channel. 300 and 200 Jlm diameter, 40 rom long, hydrogen-filled capillary discharge waveguides have been investigated. The plasma channel has the dual purpose of guiding the laser pulses over distances of many Rayleigh lengths and acting· as the nonlinear medium for the Raman instability. Laser energy transmission through the plasma channel, in single mode propagation, is observed ~o be better than 80 % for the pulses with intensities up to 5.8 X 1014 W cm-2. The dependence of the gain on pump intensity and plasma density is experimentally studied and confirms theoretical predictions. It is shown that higher pump intensities inside the capillary can be realised using unmatched guiding due to periodic oscillations ofthe laser beam waist along the plasma channel. Amplification of the seed pulse in the linear regime is obtained when the frequency detuning between the seed and the pump matches th~ plasma frequency. Thus the frequency difference between the pump and gain peaks enables to estimate the plasma density, measured around 1018 cm-3. The high gain regime has been investigated showing that peak gains of over 1200 % can be routinely realised. A peak gain of almost 3000 % has 'been observed under optimal conditions with the highest densities and pump energies. Several diagnostic systems have been developed for simultaneous detection of the spectral and energy gain together with the duration of the seed. Ultrashort pulse high gl;lin amplification of 80 fs, 5 mJ pulse has been demonstrated, giving a peak value of 800% and energy gain of 40 % together with 40 % increase in pulse duration. Amplification ofthe whole seed pulse spectra has been demonstrated using an optical cut-off filter to provide a sufficient detul1ed seed pulse. Future increase of the efficiency will occur in the nonlinear regime of the stimulated Raman backscattering resulting in compression ofthe seed pulse.
Supervisor: Not available Sponsor: Not available
Qualification Name: University of Strathclyde, Department of Physics, 2007 Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.486537  DOI: Not available
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