GENERATION OF MULTICOLOR STIMULATED RAMAN EMISSION FROM 2-COLOR LINEARLY OR CIRCULARLY POLARIZED PUMP BEAMS

A laser beam at two different frequencies separated by 587 cm-1 is focused into pressurized hydrogen (rotational transition energy, 587 cm-1) to generate multi-color stimulated Raman emission. The polarization state and the pulse energy are measured for each generated emission line using linearly and circularly polarized pump beams. The effect of the polarization is discussed by using a parameter characterizing the polarizability of hydrogen and a conservation rule for the angular momentum in four-wave mixing. Many rotational lines are generated with linearly polarized pump beams through a four-wave mixing process. This is in striking contrast to the results obtained by using a single-color circularly polarized pump beam which generates only one rotational line through a conventional stimulated Raman process.