Abstract-Terahertz generation by optical rectification in chalcopyrite crystals ZnGeP2, CdGeP2 and CdSiP2

Herath P. Piyathilaka, Rishmali Sooriyagoda, Vikum Dewasurendra, Matthew B. Johnson, Kevin T. Zawilski, Peter G. Schunemann, and Alan D. Bristow

Fig. 1 (a) Photographs of the polished CdGeP2 (CGP), ZnGeP2 (ZGP) and CdSiP2 (CSP) crystals from top to bottom. Visible light is reflected from the CGP. (b) Tauc plot for absorption edges using direct-gap normalization.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-12-16958

Optical rectification of near-infrared laser pulses generates broadband terahertz radiation in chalcopyrite crystals CdGeP2, ZnGeP2 and CdSiP2. The emission is characterized using linear-polarized excitation from 0.8 eV to 1.55 eV (1550 nm – 800 nm). All three crystals are (110)-cut and polished to 0.5 mm, thinner than the coherence length across most of the excitation photon energy range, such that they all produce a bandwidth ~2.5 THz when excited with ~100 fs pulses. It is found that CdGeP2 produced the strongest emission at telecoms wavelengths, while CdSiP2 is generally the strongest source. Pump-intensity dependence provides the nonlinear coefficients for each crystal.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-White powder identification using broadband coherent light in the molecular fingerprint region

Luke Maidment, Peter G. Schunemann, and Derryck T. Reid

(a) Scanning Michelson interferometer used to modulate the OPO idler beam (green) and the HeNe displacement-calibration beam (red). (b) Actual layout, with voice-coil actuator.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-19-25364

We show that a variety of white powder samples, including painkillers, amino acids, stimulants and sugars are readily discriminated by diffuse reflectance infrared spectroscopy involving no preparation of the sample and no physical contact with it. Eleven powders were investigated by illuminating each sample with broadband coherent light in the 8–9-µm band from an OPGaP femtosecond optical parametric oscillator. The spectra of the scattered light were obtained using Fourier-transform spectroscopy. Similarities between different spectra were quantified using Pearson’s correlation coefficient, confirming that spectral features in the 8–9-µm wavelength region were sufficient to discriminate between all eleven powders evaluated in the study, offering a route to simple and automated non-contact chemical detection.

Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Abstract-Terahertz emission from ZnGeP2: phase-matching, intensity, and length scalability

Joseph D. Rowley, Derek A. Bas, Kevin T. Zawilski, Peter G. Schunemann, and Alan D. Bristow    

http://www.opticsinfobase.org/josab/abstract.cfm?uri=josab-30-11-2882

Abstract

Collinear phase-matched optical rectification is studied in ZnGeP₂ pumped with near-infrared light. The pump-intensity dependence is presented for three crystal lengths (0.3, 1.0, and 3.0 mm) to determine the effects of linear optical absorption, nonlinear optical absorption, and terahertz free-carrier absorption on the generation. Critical parameters such as the coherence length (for velocity matching), dispersion length (for linear pulse broadening), and nonlinear length (for self-phase modulation) are determined for this material. These parameters provide insight into the upper limit of pulse intensity and crystal length required to generate intense terahertz pulses without detriment to the pulse shape. It is found that 1 mm thick ZnGeP₂(012), pumped at 1.28 μm with intensity of ∼15  GW/cm², will produce intense undistorted pulses, whereas longer crystals or larger intensities modify the pulse shape to varying degrees. Moreover, phase-matching dispersion maps are presented for the terahertz generation over a large tuning range (1.1–2.4 μm) in the longer (3 mm) crystal, demonstrating the phase-matching bandwidth and phase mismatch that leads to fringing associated with multipulse interference. All observed results are simulated numerically showing good qualitative agreement.
© 2013 Optical Society of America