Fourier-transform infrared spectroscopy with undetected photons from high-gain spontaneous parametric down-conversion

Abstract

Fourier-transform infrared spectroscopy (FTIR) is an indispensable analytical method that allows label-free identification of substances via fundamental molecular vibrations. However, the sensitivity of FTIR is often limited by the low efficiency of mid-infrared (MIR) photodetectors. SU(1,1) interferometry has previously enabled FTIR with undetected MIR photons via spontaneous parametric down-conversion in the low-parametric-gain regime, where the number of photons per mode is much less than one and sensitive photodetectors are needed. In this work, we develop a high-parametric-gain SU(1,1) interferometer for MIR-range FTIR with undetected photons. Using our new method, we demonstrate three major advantages: a high photon number at the interferometer output, a considerably lower photon number at the sample, and improved interference contrast. In addition, we analyze different methods to broaden the spectral range of the interferometer by aperiodic poling and temperature gradient in the gain medium. Exploiting the broadband SU(1,1) interferometer, we measure and evaluate the MIR absorption spectra of polymers in the 3-μm region.

17 pages, 14 figures

References in corpus (7)

• Nonlinear interferometer for Fourier-transform mid-infrared gas spectroscopy using near-infrared detection
• High-speed mid-infrared single-photon upconversion spectrometer
• Pump depletion in parametric down-conversion with low pump energies
• Generation of monocycle squeezed light in chirped quasi-phase-matched nonlinear crystals
• Single-photon time-stretch infrared spectroscopy
• Broadband spectroscopy and interferometry with undetected photons at strong parametric amplification
• A multimodal laser-scanning nonlinear optical microscope with a rapid broadband Fourier-transform coherent Raman modality

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• Sensing Birefringence and Diattenuation with Undetected Light
• Low-coherence interferometry with undetected mid-infrared photons in the high-gain regime
• Limitations of Entangled Two-Photon Absorption detection
• Two-dimensional fluorescence spectroscopy with quantum entangled photons: Idler-referenced timing without pump detection