Anisotropy of multiphoton carrier generation in monocrystalline IIa diamond and its dependence on the polarization state of excitation light (near-infrared few-cycle laser pulses) are investigated using photoluminescence and nonlinear absorption measurements. We observe anisotropy between multiphoton transition rates for light linearly polarized along the 〈100〉 and 〈110〉 crystallographic directions of diamond and a strong intensity-dependent decrease of the transition rate for circularly polarized light. Measured results are compared with numerical simulations using time-dependent density functional theory and with an analytical model assuming a parabolic two-band system and the Houston function as the time-dependent wave function of the valence and conduction bands.

Coupling between ultrafast lattice dynamics and electronic polarization becomes increasingly important for generating terahertz frequency combs, monitor atomic potential landscapes, or high-speed information processing. Here, we show that the carrier population excited by multiphoton (5-photon) absorption in diamond crystal can be controlled at terahertz frequencies by coherent lattice vibrations-phonons. We introduce and compare two independent methods for direct monitoring of coherent phonon dynamics in diamond by using photoluminescence or photocurrent measurements on femtosecond time scale. We observe a strong signal enhancement compared to standard techniques due to transmission geometry and high-order nonlinearity of optical carrier generation.

Amorphous germanium films on nonrefractory glass substrates were annealed by ultrashort near-infrared (1030 nm, 1.4 ps) and mid-infrared (1500 nm, 70 fs) laser pulses. Crystallization of germanium irradiated at a laser energy density (fluence) range from 25 to 400 mJ/cm² under single-shot and multishot conditions was investigated using Raman spectroscopy. The dependence of the fraction of the crystalline phase on the fluence was obtained for picosecond and femtosecond laser annealing. The regimes of almost complete crystallization of germanium films over the entire thickness were obtained (from the analysis of Raman spectra with excitation of 785 nm laser). The possibility of scanning laser processing is shown, which can be used to create films of micro- and nanocrystalline germanium on flexible substrates.