Optical anisotropy of NbOCl2

Abstract

Guo et al, 2023, report that NbOCl2 is a novel thin-material SPDC source, but further optical measurements on thicker samples of the material suggest that NbOCl2 does not behave like conventional SPDC producing materials. In this paper, we report the following: (1) NbOCl2 is not completely transparent at the reported pump wavelength of 404 nm, (2) NbOCl2 behaves as a polarizer at 405 nm, (3) coincidences above noise level around 810 nm were obtained when pumping NbOCl2 at 405 nm and varied with pump polarization, and (4) pumping at the more transparent wavelength of 780 nm fails to yield any detectable SPDC photon pairs.