Spontaneous-Raman-Scattering Efficiency and Stimulated Scattering in Silicon

The absolute spontaneous-Raman-scattering efficiency and linewidth of the 521-${\mathrm{cm}}^{-1\mathrm{}}$ optical mode of silicon have been measured at 77 K using a continuous laser (Nd in yttrium aluminum garnet) operating at 1.064 μm. The measured scattering efficiency (5.1 × ${10}^{-6\mathrm{}}$/cm sr for unpolarized forward scattering along the crystal [111] direction) and narrow linewidth yield a calculated value of the stimulated Raman gain coefficient which is considerably larger than those reported for other media, both solid and liquid. Stimulated Raman scattering in Si at 77 K has also been observed using a focused multimode $Q$-switched YAG: Nd laser. Inaccuracy in the measured stimulated gain resulted mainly from the uncertainty in the effective focal volume inside the silicon. Multiphoton absorption at the incident laser frequency has been considered and found to modify the measured stimulated gain by a significant amount. The estimated gain from the stimulated Raman effect was found to be in satisfactory agreement with that calculated from the absolute spontaneous-Raman-scattering efficiency.