Prospects of using novel nonlinear crystals in SU(1,1) interferometry

Abstract Nonlinear interferometry presents a powerful approach for infrared metrology by enabling measurements with visible or near-infrared detectors. In this study, we evaluate the potential of novel nonlinear crystals for mid-infrared ‘fingerprint’ spectroscopy based on nonlinear interferometry, focusing on the transparency range, nonlinear coefficients, and phase-matching capabilities of nonlinear crystals. We compare established materials like silver thiogallate (AgGaS 2 ) with promising alternatives, including mercury thiogallate (HgGa 2 S 4 ), barium gallium germanium sulphide (BaGa 2 GeS 6 ), and barium gallium germanium selenide (BaGa 2 GeSe 6 ). The selected nonlinear crystals exhibit higher nonlinear conversion efficiency compared to AgGaS 2 , with BaGa 2 GeS 6 additionally offering a narrower angular spectrum of spontaneous parametric down conversion, advantageous in interferometric schemes. Our findings establish a pathway for integrating advanced crystal technologies into mid-infrared metrology and imaging systems, setting the stage for future developments in nonlinear interferometry and spectroscopy.