Collinear Difference Frequency Generation Research Articles

Tunable and coherent terahertz source based on CdSiP2 crystal via collinear difference frequency generation.

CdSiP2 (CSP) crystals have attracted increasing attention as efficient optical conversion media. Herein, the optical properties of a CSP crystal grown with the vertical Bridgman method are measured by a terahertz time-domain spectrometer (THz-TDS) at 0.2-3 THz. For the first time, to the best of our knowledge, the broadband, tunable, coherent, monochromatic THz radiation from 0.08 to 1.68 THz (3775-178 µm) is generated experimentally via this crystal, which is pumped by a nanosecond Q-switched Nd:YAG laser and an optical parametric oscillator (OPO) and based on difference frequency generation (DFG) technology. The output power and its corresponding conversion efficiency at 0.74 THz are 26.6 mW and 1.4 × 10-7, respectively. Our work demonstrates that the CSP crystal is a potential efficient terahertz DFG candidate for out-of-door applications.

Intensive terahertz emission from GaSe0.91S0.09 under collinear difference frequency generation

An intensive, broad tunable monochromatic Terahertz (THz) emission is generated from S-doped (2 wt. %) GaSe (solid solution GaSe0.91S0.09) crystals by collinear difference frequency generation method. The generated THz signal of 3.8 ns covers the spectral range of 0.57–3.57 THz (84.0–528.0 μm), with a maximal THz output peak power of 21.8 W at 1.62 THz. The THz power conversion efficiency is of 45% higher than that of undoped GaSe, which is mainly contributed to the improved optical properties. The terahertz source is of great potential to be exploited for the out-of-door applications due to the increased crystal hardness.

Investigation of high power terahertz emission in gap crystal based on collinear difference frequency generation

Among many terahertz wave generation methods, nonlinear optical collinear difference frequency generation (CDFG) is always regarded as a promising way to achieve the high power, broadband, continual tunable terahertz wave emission. Theoretical analysis shows that a big coherent length (on millimeter scale) in isotropic GaP crystal could be realized by the laser wavelength near 1064 nm in the CDFG process, which meets the condition of high power and broadband terahertz generation. In the experiment, a high power and broadband terahertz wave is achieved from GaP crystal, with its tunable terahertz range 95.9-773.4 μm (0.39-3.13 THz) and the highest terahertz peak power 7 W at 2 THz. The experimental result is generally consistent well with its theoretical calculation.

Cascaded carbon monoxide laser frequency conversion into the 43–49 μm range in a single ZnGeP_2 crystal

Collinear cascaded mid-IR frequency conversion in a single nonlinear optical crystal was accomplished. Concurrent collinear generation of the sum frequency of multiline fundamental band carbon monoxide laser radiation as a first frequency conversion cascade resulted in collinear difference frequency generation within the 4.3 to 4.9 μm spectral range when mixing this sum frequency radiation with the fundamental one as the second cascade in the same ZnGeP(2) nonlinear optical crystal.

New method to determine the refractive index and the absorption coefficient of organic nonlinear crystals in the ultra-wideband THz region

A method for simultaneously measuring the refractive index and absorption coefficient of nonlinear optical crystals in the ultra-wideband terahertz (THz) region is described. This method is based on the analysis of a collinear difference frequency generation (DFG) process using a tunable, dual-wavelength, optical parametric oscillator. The refractive index and the absorption coefficient in the organic nonlinear crystal DAST were experimentally determined in the frequency range 2.5-26.2 THz by measuring the THz-wave output using DFG. The resultant refractive index in the x-direction was approximately 2.3, while the absorption spectrum was in good agreement with FT-IR measurements. The output of the DAST-DFG THz-wave source was optimized to the phase-matching condition using the measured refractive index spectrum in THz region, which resulted in an improvement in the output power of up to a factor of nine.

Compact and widely tunable terahertz source based on a dual-wavelength intracavity optical parametric oscillation

In this paper, a continuously tunable terahertz (THz) source is obtained using a compact intracavity pumped dual-wavelength optical parametric oscillation operating around 2.1 μm as difference-frequency generation pump source. The tuning range of the THz-wave frequency covers from 0.147 THz to 3.651 THz. Based on the collinear difference-frequency generation in the GaSe crystal, the experiment result shows that our schematic is a good option to construct a compact and portable terahertz source with widely tunable range.