Laser-induced free-carrier and temperature gratings in silicon

Dynamic gratings have been produced in silicon excited with nano- and picosecond pulses at 1.06 μm wavelength and then probed at 1.06 and 1.3 μm. The diffraction efficiency is given by a Bessel function of the refractive-index change. The resulting modulation of the diffracted light experimentally proves that the phase-grating contribution is dominant. Free-carrier and thermal refractive-index changes are separated due to their different time dependences and opposite signs. The dispersion volume $n_{e\mathrm{-}h}$=1.4×${10}^{\mathrm{-}21}$ ${\mathrm{cm}}^3$ of the electron-hole pairs at 1.3 μm was measured. The time dependence of the diffraction efficiency is described by diffusion and recombination of the electron-hole pairs and by heat conduction.