Stimulated Raman scattering and four-wave Raman mixing seeded by a supercontinuum generated in dibromomethane using picosecond and femtosecond laser sources

Stimulated Raman emission from liquid dibromomethane (vibrational Raman shi ft frequency, 588 cm(-1)) is introduced into hydrogen gas (rotational Raman shift frequency, 587 cm(-1)) as a seed beam, in order to generate numerous rotational lines by four-wave Raman mixing. Unexpectedly, a supercontinuum , which is generated by self-phase modulation in dibromomethane, acted as a seed beam to exclusively generate vibrational lines; the rotational lines are generated only when the supercontinuum is minimal. The former is explai ned by a competition between the high-gain vibrational and low-sain rotatio nal Raman effects when strongly seeded by a supercontinuum. The latter is e xplained by stimulated Raman gain under the seed effect exclusively to the first-Stokes rotational line. (C) 1999 Elsevier Science B.V. All rights res erved.