We demonstrate the generation muJ-level, single-cycle terahertz pulses by optical rectification from a large-aperture ZnTe single crystal wafer. Energies up to 1.5 muJ per pulse and a spectral range extending to 3 THz were obtained using a 100 Hz Ti:sapphire laser source and a 75-mmdiameter, 0.5-mm-thick, (110) ZnTe crystal, corresponding to an average power of 150 muW and an energy conversion efficiency of 3.1 x 10(-5). We also demonstrate real-time imaging of the focused terahertz beam using a pyroelectric infrared camera.
Polarized second-harmonic generation and terahertz radiation in reflection from ͑100͒, ͑110͒, and ͑111͒ faces of n-type InAs crystals are investigated as a function of the sample azimuthal orientation under excitation from femtosecond Ti:sapphire laser pulses. The expressions describing the second-order response ͑optical secondharmonic generation and optical rectification͒ in reflection from zinc-blende crystals, such as InAs, are calculated taking into account the bulk electric-dipole contribution and the first-order surface electric-field-induced contribution. It is shown that the two contributions can be separated based on rotation symmetry considerations. Moreover, a direct comparison of the second-harmonic generation and terahertz radiation emission indicates that the observed dominant surface electric-field-induced optical rectification component may be attributed to the large free-carrier contribution to the third-order susceptibility in InAs.
The far-infrared properties of spruce wood are examined with a terahertz time-domain spectrometer. The solid wood is shown to exhibit both birefringence and diattenuation. The birefringence properties are sufficient for construction of a quarter-wave plate operating at 0.36 THz, and a half-wave plate operating at 0.71 THz. The origin of the birefringence is attributed to preferential fiber orientation within the wood. Similar birefringence is observed in lens paper in which the fibers are preferentially oriented in one direction.
Using a chirped pulse probe technique, we have obtained single-shot measurements of temporal evolution of ac conductivity at 1.55 eV (800 nm) during electron energy relaxation in nonequilibrium warm dense gold with energy densities up to 4.1 MJ/kg (8×10(10) J/m3). The results uncover important changes that have been masked in an earlier experiment. Equally significant, they provide valuable tests of an ab initio model for the calculation of electron heat capacity, electron-ion coupling, and ac conductivity in a single, first principles framework. While measurements of the real part of ac conductivity corroborate our theoretical temperature-dependent electron heat capacity, they point to an electron-ion coupling factor of ∼2.2×10(16) W/m3 K, significantly below that predicted by theory. In addition, measurements of the imaginary part of ac conductivity reveal the need to improve theoretical treatment of intraband contributions at very low photon energy.
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