Infrared metrology using visible light

• Main Author: Paterova, Anna
• Other Authors: Soci Cesare
• Format: Theses and Dissertations
• Language: English
• Published: 2019
• Subjects: DRNTU::Engineering::Electrical and electronic engineering
• Online Access: https://hdl.handle.net/10356/103485; http://hdl.handle.net/10220/47387
• Institution: Nanyang Technological University

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.