Quantum Fourier-Transform Infrared Spectroscopy for Complex Transmittance Measurements

Abstract

Harnessing the quantum interference of the pair generation processes, infrared quantum spectroscopy, based on nonlinear interferometers with visible-infrared photon-pair sources, enables the extraction of the infrared optical properties of a sample through visible photon detection without the need for an infrared optical source or detector. We develop a theoretical framework for quantum Fourier-transform infrared (QFTIR) spectroscopy. The proposed Fourier analysis method, which fully utilizes the phase information in the interferogram, allows us to determine the complex transmittance and optical constants for a sample in a simple setup without the use of any dispersive optics for spectral selection. In the experimental demonstrations, the transmittance spectrum of a bandpass filter and the refractive index of silica glass are measured in the near-infrared region using QFTIR operated in a low gain regime; these results agree well with the independently measured spectrum using a conventional spectrometer and an value estimated from references. These demonstrations prove the validity and great potential of QFTIR spectroscopy.