Abstract
An amplification process was investigated in the third stimulated Raman scattering (SRS) line of excited with a laser beam generated from the fourth harmonic of a Nd:YAG laser. The unexpected intensity enhancement observed at the third Stokes SRS line around is attributed to the seeding of the self-generated Balmer line at of atomic hydrogen by pumping the molecule with a high-energy laser pulse at . It is worth mentioning that in our case the SRS spectrum of showed a quite different intensity pattern from the usual SRS spectra of hydrogen. The pulse energy and pressure dependence of all the SRS lines in general and the third Stokes SRS line in particular were investigated, and in all respects the amplified SRS line at manifested completely different characteristics that have not been reported in previous publications. The conversion efficiency (CE) of all the SRS lines in the hydrogen SRS spectrum was also estimated, and 36% CE was achieved at the line. To support our claim for amplification at the third Stokes line by seeding of the Balmer line of atomic hydrogen, a comparative study was also carried out by pumping hydrogen gas with (less energy per photon) and laser beams. It is worth noting that amplification of the third Stokes SRS line was observed only with the pump laser, where dissociation of and excitation of atomic hydrogen take place, and not with the pump laser.
© 2008 Optical Society of America
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