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 down-conversion. 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.

中文翻译：

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指纹中红外区域的宽带量子光谱

许多分子在“指纹”红外 (IR) 区域表现出独特的吸收带，从而可以进行化学鉴定和检测。这使得红外光谱成为生物医学诊断、传感和材料表征的重要工具。然而，由于性能相对较差、需要低温冷却以及 IR 光源和光电探测器的高成本，IR 范围内的测量具有挑战性。在这里，我们证明了样品的中红外指纹可以通过使用传统硅光电探测器在近红外范围内的测量来揭示。我们的方法依赖于强频率非简并参数下转换中产生的相关光子对的量子干涉。我们的技术同时以高精度测量宽“指纹”区域的吸收系数和折射率。作为概念验证，我们在 7.4 到 8.4 μm 波长范围内对一氧化二氮气体进行光谱分析，在 865 到 877 nm 范围内进行检测。这项工作将量子干涉仪的适用性扩展到了一系列广泛的实际应用，例如大气污染物的检测、呼吸诊断、化学安全等。