Abstract We demonstrate the use of a nonlinear interferometer with bulk lithium niobate crystal for sensing of gas mixtures over broadband mid-infrared (mid-IR) range of wavelengths. Our method utilizes spontaneous parametric down-conversion to generate correlated photon pairs in the visible and mid-IR ranges. We show that by leveraging the phase-matching properties of lithium niobate crystal, it is possible to access the ‘fingerprint’ region of greenhouse gases in the mid-IR range by detection of correlated visible light signal. Our technique enables simultaneous detection of gas mixtures with high spectral resolution and fast readout without the need for specialized mid-IR equipment. The experimental results show its applicability to molecular gas sensing, paving the way for new advancements in environmental monitoring.
Abstract We demonstrate the use of a nonlinear interferometer with bulk lithium niobate crystal for sensing of gas mixtures over broadband mid-infrared (mid-IR) range of wavelengths. Our method utilizes spontaneous parametric down-conversion to generate correlated photon pairs in the visible and mid-IR ranges. We show that by leveraging the phase-matching properties of lithium niobate crystal, it is possible to access the ‘fingerprint’ region of greenhouse gases in the mid-IR range by detection of correlated visible light signal. Our technique enables simultaneous detection of gas mixtures with high spectral resolution and fast readout without the need for specialized mid-IR equipment. The experimental results show its applicability to molecular gas sensing, paving the way for new advancements in environmental monitoring.
Nonlinear interferometers based on non-degenerate spontaneous parametric down-conversion (SPDC) create a link between separate spectral ranges. This allows for measurements in remote spectral regions while detecting light in easily accessible wavelengths. In our work, we use periodically poled lithium niobate to create correlated signal (visible or near-infrared) and idler (mid-infrared) photon pairs. Using a nonlinear interferometer in Michelson geometry, we obtain broadband mid-infrared spectra from light detected with a silicon avalanche photodiode. Combining the nonlinear interferometer with a measurement scheme in close analogy to classical Fourier-transform infrared spectroscopy allows for sub-wavenumber spectral resolution, which opens up possibilities for applications such as precise spectroscopic gas analysis.
High Resolution Image Download MS PowerPoint Slide 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.
Spontaneous parametric down-conversion is an essential tool for a quantum light source in the infrared region ranging 2-5 µm for the purpose of material identification, chemical analysis, and gas sensing. So far, photon pairs from the process in a nonlinear crystal have low tunability and a narrow spectral range because of the phase-matching condition. Here, we propose a novel type of spontaneous parametric down-conversion processes that overcomes these challenges, where two photon pairs are simultaneously produced in the visible and infrared regions in periodically poled stoichiometric lithium tantalite. It allows broadband and tunable generation of infrared photon pairs that can be employed as an alternative light source for quantum infrared spectroscopy.
Optical coherence tomography (OCT) is an appealing technique for bio-imaging, medicine, and material analysis. For many applications, OCT in mid- and far-infrared (IR) leads to significantly more accurate results. Reported mid-IR OCT systems require light sources and photodetectors which operate in mid-IR range. These devices are expensive and need cryogenic cooling. Here, we report a proof-of-concept demonstration of a wavelength tunable IR OCT technique with detection of only visible range photons. Our method is based on the nonlinear interference of frequency correlated photon pairs. The nonlinear crystal, introduced in the Michelson-type interferometer, generates photon pairs with one photon in the visible and another in the IR range. The intensity of detected visible photons depends on the phase and loss of IR photons, which interact with the sample under study. This enables us to characterize sample properties and perform imaging in the IR range by detecting visible photons. The technique possesses broad wavelength tunability and yields a fair axial and lateral resolution, which can be tailored to the specific application. The work contributes to the development of versatile 3D imaging and material characterization systems working in a broad range of IR wavelengths, which do not require the use of IR-range light sources and photodetectors.
Mid-infrared (mid-IR) spectra revealing the distinct “fingerprint” of molecules are of critical importance for both science and technology in chemistry, physics, materials science, and biology. Mid-IR sensing and spectroscopy provide unique and powerful tools for crucial applications in greenhouse gas monitoring, hazardous emission detection, and medical breath diagnosis. However, the low-photon energy characteristic of the mid-IR spectrum poses significant challenges for both mid-IR light sources and detectors, hindering their compact and cost-efficient applications in various areas. Here, we experimentally demonstrate mid-IR gas spectroscopy without mid-IR photons solely using convenient near-IR optical components. This is realized by generating photon pairs (i.e., a mid-IR photon and a near-IR one) through a spontaneous parametric downconversion in a microscale optical cavity. The generation rate of near-IR photons strongly relies on the absorption of the mid-IR photon due to their quantum correlation. Through interacting with evanescent fields around the microcavity, the absorptive mid-IR resonances of the surrounding gas greatly affect the detected near-IR photons without harassing any mid-IR photon. This scheme presents a cost-effective and compact solution for on-chip quantum gas spectroscopy without requiring expensive mid-IR lasers and detectors or lasers, thereby paving new avenues for applications in environmental monitoring/safety, healthcare, and agriculture.
Infrared (IR) spectroscopy and imaging are important tools in metrology, including material analysis, sensing and characterization. Although conventional methods of IR metrology are available, they face challenges related to the high cost and low efficiency of IR light sources and photodetectors. These challenges can be addressed by circumventing the need for IR-range components using tools and techniques of quantum optics. In this thesis, we describe a technique for IR measurements, which requires using only accessible light sources and detectors operating in the visible range. Our technique is based on the nonlinear interference of correlated photon pairs generated via spontaneous parametric down conversion (SPDC). In SPDC, a photon from the pump laser generates a pair of correlated photons within a nonlinear crystal. One photon of the pair can be generated in the visible range, and the other in the IR range. Two identical nonlinear crystals pumped by the same laser form the nonlinear interferometer, where interference of the visible SPDC photons can be observed. The interference pattern of the visible photons depends on amplitudes and phases of the IR photons, which are used to probe the properties of the medium under study. Hence, by observing the interference of the visible photons we infer the IR properties of the media, without direct measurements of IR light. We applied the nonlinear interference method to realize the IR spectroscopy, IR optical coherence tomography (OCT), IR imaging and IR polarimetry. In the IR spectroscopy experiment, we simultaneously and independently measured both refractive index and absorption coefficient of various samples in the IR range, while only detecting photons in the visible range. In IR OCT and IR imaging schemes, we measured the reflectivity of the interfaces of the sample, performed 3D raster and wide field imaging through opaque (in the visible range) materials. In the IR polarimetry, we measured the birefringence of the samples. We studied glass, organic polymer, Silicon and CO2 gas, but our method can be applied to a broad variety of samples. Our method is widely tunable and has high precision and accuracy over mid-IR wavelengths. This work paves the way for further practical adoption of the method in the field of IR metrology, without the need for IR grade detectors and sources.