Physical origins of double peak phase matching in GaSe

Double peak phase matching was recorded during experimental study of parametric frequency converters based on GaSe, its solid solutions crystals like GaSe1-xSx and ZnGeP2. Its physical origins are identified as presence of twin, large difference between cut and PM angles, self-heating effect at appropriate conditions, mismatched second (Φ) phase matching angle and microdefects. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Giant non-linear susceptibility of hydrogenic donors in silicon and germanium

Implicit summation is a technique for the conversion of sums over intermediate states in multiphoton absorption and the high-order susceptibility in hydrogen into simple integrals. Here, we derive the equivalent technique for hydrogenic impurities in multi-valley semiconductors. While the absorption has useful applications, it is primarily a loss process; conversely, the non-linear susceptibility is a crucial parameter for active photonic devices. For Si:P, we predict the hyperpolarizability ranges from $\chi^{(3)}/n_{\text{3D}}=2.9$ to $580 \times 10^{-38}$ $\text{m}^5/\text{V}^2$ depending on the frequency, even while avoiding resonance. Using samples of a reasonable density, $n_{\text{3D}}$, and thickness, $L$, to produce third-harmonic generation at 9 THz, a frequency that is difficult to produce with existing solid-state sources, we predict that $\chi^{(3)}$ should exceed that of bulk InSb and $\chi^{(3)}L$ should exceed that of graphene and resonantly enhanced quantum wells

Optical rectification and down-conversion of fs pulses into mid-IR and THz range in GaSe1-xSx

Design of top S-doped GaSe growth technology is completed. New methods for characterization of high optical quality crystals are proposed that allowed selection optimally doped crystals. Frequency conversion of fs pulses into 6.5–35 μm and into 0.2–4.5 THz is realized. S-doped crystals demonstrated advantages from 50–70% in the first experiments up to 8.5–15 times in the following experiments depending on experimental conditions. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

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

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. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

THz pulse generation in ZnGeP2 with near-IR pumping

THz wave generation was investigated in nonlinear ZnGeP2 crystals with the fs pumping at 800 nm and 950 nm. Transmission and absorption spectra were analyzed. Refractive indices of the ZnGeP2 in the THz range were measured and approximated in the form of Sellmeier equations. Phase-matching conditions were calculated. Calculated conditions are well correlated with experimental data

Doped GaSe crystals for laser frequency conversion

In this review, we introduce the current state of the art of the growth technology of pure, lightly doped, and heavily doped (solid solution) nonlinear gallium selenide (GaSe) crystals that are able to generate broadband emission from the near infrared (IR) (0.8 mm) through the mid- and far-IR (terahertz (THz)) ranges and further into the millimeter wave (5.64 mm) range. For the first time, we show that appropriate doping is an efficient method controlling a range of the physical properties of GaSe crystals that are responsible for frequency conversion efficiency and exploitation parameters. After appropriate doping, uniform crystals grown by a modified technology with heat field rotation possess up to 3 times lower absorption coefficient in the main transparency window and THz range. Moreover, doping provides the following benefits: raises by up to 5 times the optical damage threshold; almost eliminates two-photon absorption; allows for dispersion control in the THz range independent of the mid-IR dispersion; and enables crystal processing in arbitrary directions due to the strengthened lattice. Finally, doped GaSe demonstrated better usefulness for processing compared with GaSe grown by the conventional technology and up to 15 times higher frequency conversion efficiency