Broadband Quantum Spectroscopy at the Fingerprint Mid-Infrared Region

Abstract

Numerous molecules exhibit unique absorption bands in the "fingerprint" infrared (IR) region, allowing chemical identification and detection. This makes IR spectroscopy an essential tool in biomedical diagnostics, sensing, and material characterization. However, measurements in the IR range are challenging due to the relatively poor performance, need for cryogenic cooling, and high cost of IR light sources and photodetectors. Here, we demonstrate that the mid-IR fingerprints of the sample can be revealed from measurements in the near-IR range using conventional silicon photodetectors. Our approach relies on the quantum interference of correlated photon pairs produced in strong frequency nondegenerate parametric downconversion. Our technique simultaneously measures the absorption coefficient and refractive index in the broad "fingerprint" region with high accuracy. As a proof-of-concept, we perform spectroscopy of nitrous oxide gas in the 7.4 to 8.4 μm wavelength range, with the detection in the 865 to 877 nm range. This work extends the applicability of quantum interferometry to a range of broad practical appeals, such as detection of atmosphere pollutants, breath diagnostics, chemical safety, and others.

A Facile Raman Spectroscopy Method for Online Monitoring of Crystal Plane Orientation of Favipiravir

“…This work primarily focuses on the spectral peak analysis of the fingerprint area since it is well known that the vibrational modes in the 400-1350 cm -1 fingerprint region are very sensitive to changes in molecular structure 34) . We used DFT to analyze the vibrational modes of favipiravir molecules, which helped with the assignment of the spectra, in particular the attribution of bands to vibrational modes associated with specific surface structures (Table 1).…”

Mid-infrared single-photon upconversion spectroscopy enabled by nonlocal wavelength-to-time mapping

“…To overcome these main limitations, MIR spectroscopic measurement based on nonlinear effects emerges as a promising option. The nonlinear interferometry based on the phenomenon of induced coherence has received much attention in the realm of MIR spectroscopy (17)(18)(19)(20). Correlated photons are proposed to circumvent the need for MIR detectors since MIR idler photons from spontaneous parametric downconversion (SPDC) do not need to be monitored in this technique.…”

Quantum optical induced-coherence tomography by a hybrid interferometer

“…Therefore, changes in the probe photon path by a target are measurable with interferometry for the signal photons, and the probe photons need not be measured eventually because their existence is guaranteed through energy conservation. This induced-coherence phenomenon, observed since 1991 [8,9], has led to the demonstration of optical measurement techniques with ever-increasing complexity, such as optical on-off imaging [5], spectroscopy [10,11], optical coherence tomography (OCT) [12][13][14][15], microscopy [16,17], Fourier-transform infrared (IR) spectroscopy [18,19] and holography [20].…”