Multiplication of spectral lines generated by two-color stimulated raman effect

A dye laser emitting at four different frequencies separated by 293.5 (=587/2) cm^-1 is made by inserting an etalon in the resonator cavity of the laser. This laser beam is focused into molecular hydrogen (rotational Raman shift frequency, 587 cm^-1) to generate a multicolor laser beam consisting of more than 10 rotational lines in the vicinity of the fundamental lines by four-wave Raman mixing. Such rotational lines also occur in the vicinity of the vibrational Raman lines. Thus more than 25 emission lines appear simultaneously. This approach is useful to multiply the line density, i.e., the emission lines within a specified wavelength region.