Nonlinear infrared spectroscopy free from spectral selection

TL;DR

This paper introduces a novel IR spectroscopy method using visible light optics and entangled photons, enabling material analysis in the IR range without traditional IR components, thus reducing cost and improving performance.

Contribution

The authors develop a nonlinear interferometry technique using entangled photons that allows IR property measurement with visible light equipment, eliminating the need for IR spectrometers.

Findings

Achieves higher signal-to-noise ratio than previous methods.

Enables IR property measurement using only visible light detectors.

Does not require spectrometers or slits, simplifying the setup.

Abstract

Infrared (IR) spectroscopy is an indispensable tool for many practical applications including material analysis and sensing. Existing IR spectroscopy techniques face challenges related to the inferior performance and the high cost of IR-grade components. Here, we develop a new method, which allows studying properties of materials in the IR range using only visible light optics and detectors. It is based on the nonlinear interference of entangled photons, generated via Spontaneous Parametric Down Conversion (SPDC). In our interferometer, the phase of the signal photon in the visible range depends on the phase of an entangled IR photon. When the IR photon is traveling through the media, its properties can be found from observations of the visible photon. We directly acquire the SPDC signal with a visible range CCD camera and use a numerical algorithm to infer the absorption coefficient and the refraction index of the sample in the IR range. Our method does not require the use of a spectrometer and a slit, thus it allows achieving higher signal-to-noise ratio than the earlier developed method.