Physical review. B, Condensed matter
Infrared transient grating and photon echo spectroscopy of oxygen vibrational modes in amorphous silicon thin films
Jon‐Paul R. Wells, Paul J. Phillips, Nicolae Tomozeiu, F.H.P.M. Habraken, J. I. Dijkhuis
Abstract
We report on picosecond coherent transient spectroscopy on the asymmetric stretching mode in $a\ensuremath{-}{\mathrm{SiO}}_{0.1}$ thin films using the Dutch free-electron laser FELIX. A fast 10-K lifetime of 2.8 ps is obtained using laser-induced transient grating spectroscopy. Its thermal behavior suggests relaxation into two accepting modes possibly via the symmetric stretch mode of the Si-O-Si complex. Two-pulse photon echo measurements reveal phase dynamics with both an excitation density and temperature dependence, suggesting the presence of nonequilibrium Si-Si phonons. The temperature-dependent component of the pure dephasing may be attributable to two-phonon elastic scattering. From the probe pulse diffraction efficiency, a value of the nonlinear refractive index has been determined to be ${n}_{2}=3.73\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}{\mathrm{cm}}^{2}/\mathrm{GW}.$