Two-photon stimulated Raman excitation of thermal laser-induced gratings in molecular gases using broadband radiation of a single laser.

For the first time to our knowledge, thermal laser-induced gratings (LIGs), generated via two-photon stimulated Raman excitation of pure rotational (and low-lying vibrational) transitions in molecules employing broadband radiation of a single pump laser, are observed. The efficiency of LIGs excitation using a few ns pulse duration dye laser with the spectral width of about 400 cm(-1), which covers the frequency range of the characteristic rotational transitions, is experimentally investigated in a number of molecular gases (N(2), CO(2), C(3)H(8)) at room temperature and pressures of 0.1-5 bar. The physical mechanisms of LIG formation are discussed and comparison of the shapes of the LIG signals obtained in different gases is presented in relation to the spectra of rotational and vibrational energies of the molecules under study, as well as to the selection rules for Raman transitions.