G.V. Lanskii

Characterization of Bridgman grown GaSe:Al crystals

Centimeter-sized Al-doped nonlinear GaSe crystals were grown by the modified Bridgman method with heat field rotation. The alumina distribution coefficient in the grown crystals was estimated to be about 8 × 10−2 for GaSe:Al (≥0.1 at%) crystals. GaSe:Al (≤0.5 at%) crystals possess optical properties suitable for non-linear applications. For the first time the increase in the ordinary refractive index of GaSe crystals with doping was demonstrated to be different to other doped GaSe crystals.

LBO: optical properties and potential for THz application

High quality lithium borate (LBO) samples cut along (1 0 0), (0 1 0) and (0 0 1) axes were studied by terahertz time-domain spectroscopy (THz TDS) between 0.2–3 THz. It was found that in the direction of crystallographic axis X the optical absorption coefficient is the lowest amongst all known anisotropic nonlinear crystals, and that birefringence is as large as 0.42. Dispersion equations for the entire transparency range of LBO were developed for the first time. Phase matching for down-conversion into the THz range was found to be possible. Phase matching availability, low optical loss in the transparency band, and high optical damage threshold make LBO one of the most promising nonlinear materials for THz generation.

Characterization of optical quality of GaSe:Al crystals by exciton absorption peak parameters

AbstractnThe paper reports a first growth of the Al-doped GaSe crystals by modified technology with heat field rotation. These crystals shown from 2 to 3 times lower absorption coefficient at the maximal transparency range to that in crystals grown by conventional Bridgman technology. Possibility of the identification of optimal doping level in grown crystals by analysis of shape of the exciton absorption peak and intensity of the absorption shoulder at the transmission edge was demonstrated. The optimal doping can be attributed to the concentration of Al in the growth charge between 0.02 and 0.05xa0at.%. The result of the identification is confirmed by frequency conversion experiments: CO2 laser SHG and optical rectification of fs pulses.

Dispersion properties of GaS studied by THz-TDS

High optical quality centimeter sized GaS crystals are grown using a modified vertical Bridgman method with heat field rotation of the growth melt. Ordinary and extraordinary wave refractive index dispersions are studied by THz time-domain spectroscopy (THz-TDS). New dispersion equations are designed to be suitable for estimating dispersion properties of solid solution GaSe1−xSx crystals from the near IR through the mid-IR and further into the THz range.

Optical properties of PbIn6Te10 in the long-wave IR

Optical properties of nonlinear PbIn6Te10 (PIT) crystal were studied for the first time within 30–1200 µm (0.2–15 THz) by FTIR and THz-TDS. It was found that PIT possesses the most attractive transparency features for efficient generation of long-wave mid-IR emission including 20–60 µm (5–15 THz) region by optical rectification. This crystal is also found useful for phase matched DFG generation into the long-wave THz region. In particular, by model study phase matched down-conversion of CO and CO2 laser lines into 130–1200 µm (0.3–2.3 THz) range is shown possible by ooe and eoe type of three wave interaction. Noncritical 90° phase matching for eoe type of interactions can be realized by selecting samples with specified composition.

Aspects for efficient wide spectral band THz generation via CO2 laser down conversion

Detailed model study of THz generation by CO2 laser down-conversion in pure and solid solution crystals GaSe1-xSx is carried out for the first time. Both forward and backward collinear interactions of common (eo-e, oe-e, oe-o, oo-e, ee-o) and original (ee-e, oo-o) types are considered. Possibility of realization, phase matching angles and figure of merits are estimated for line mixing within 9 μm and 10 μm emission bands, as well between them. Dispersion properties of o- and e-wave refractive indices and absorption coefficients for GaSe, GaS and GaSe1-xSx crystals were preliminary measured by THz-TDS, approximated in the equation form and then used in the study. Estimated results are presented in the form of 3-D figures that are suitable for rapid analyses of DFG parameters. The most efficient type of interaction is eo-o type. Optimally doped (x = 0.09-0.13) GaSe1-xSx crystals are from 4 to 5 times more efficient at limit pump intensity than not doped GaSe crystals.

Model studies of THz-range generation by down-conversion in GaSe and GaSeS crystals

Model study of not phase matched and phase matched optical rectification or down-conversion of Ti:Sapphire laser pulses at 950 nm into THz and far-IRrange in pure and S-doped GaSe single crystals is carried out. First, the ordinary and extraordinary wave dispersions of the GaSe refractive indices were measured by terahertz time-domain spectroscopy (THz-TDS). Measured data were approximated in the form of Sellmeier dispersion equations for 0.62 – 2000 μm range with using available shorter wave data.

Modification and ab-initio spectroscopic application of modified commerce terahertz spectrometer by using homemade parts

Ab-initio study on modification of commerce terahertz spectrometer with time resolution Z-3 (Zomega, USA) by substitution of ZnTe and GaP detectors and LT-GaAs generator for homemade of pure and S-doped GaSe is carried out. It was established that in spite of not optimized parameters pure and doped GaSe:S(0.3 mass%) crystal are comparable, relatively, in generation efficiency and detection sensitivity to commerce units due to lower nonlinear optical loss and much higher damage threshold. The advantages are in force from pump fluences of below 5 mJ/cm2 for pure GaSe. The closer S-doping to optimal concentration, the lover fluences resulting in the advantages. Pure and S-doped GaSe demonstrate higher reliability and larger dynamic range of operation. Recorded absorption spectra well match known spectra.