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

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 (AgGaS2) with promising alternatives, including mercury thiogallate (HgGa2S4), barium gallium germanium sulphide (BaGa2GeS6), and barium gallium germanium selenide (BaGa2GeSe6). The selected nonlinear crystals exhibit higher nonlinear conversion efficiency compared to AgGaS2, with BaGa2GeS6 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.