Investigation of free charge carrier dynamics in single-crystalline CVD diamond by two-photon absorption

By using the methods of transient gratings (TGs) and induced absorption, we have studied the kinetics of plasma of free charge carriers (FCCs) created by the action of a picosecond laser pulse in two high-purity diamond single crystals synthesised from the gas phase. The gratings with different spatial periods have been excited at the wavelengths of 266 or 213 nm (above and below the fundamental absorption edge in diamond) and probed with continuous-wave radiation in the visible region. At the moderate FCC concentrations (~7 × 10¹⁷ cm^-3), the coefficient of ambipolar diffusion and the carrier recombination time of two crystals are 20.3 and 18.9 cm² s^-1 and 30 and 190 ns, respectively. The increase in the carrier concentration up to 5 × 10¹⁹ cm^-3 reduces the TG lifetime. We have determined the conditions under which the relaxation of the grating of carriers leads to the formation of a thermal grating, with the amplitude sufficient for its experimental observation.