Dynamics of photoexcited carriers in CVD diamond studied by mid-infrared femtosecond spectroscopy

We report on the dynamics of high-density photoexcited charge carriers in CVD diamond at low (13 K) and moderate (250 K) temperatures studied by femtosecond pump and probe spectroscopy. We measured the transient transmission at wavelengths in the mid-infrared spectral region (3-8 mu m) to study the electron-hole liquid system around its plasma frequency. Drude theory of free carrier absorption is used to determine the parameters of the electron-hole drops. For probe wavelength of 8 pm and lattice temperature of 250 K, a fast component of the transient transmission signal with the decay time similar to 38 ps is resolved in addition to a slow similar to 1.8 ns component common to all probe wavelengths. The initial picosecond decay is ascribed to the dependence of the excited carrier absorption coefficient on the effective carrier temperature. This allows us to monitor the charge carrier relaxation after optical excitation. A quantum model of free carrier absorption including the optical and acoustic phonon scattering processes is used to support our interpretation. (C) 2016 Elsevier B.V. All rights reserved.