Mid-IR Spectroscopy Achieved With Undetected Quantum Photons

Researchers at the Research Center for Non-Destructive Testing and Johannes Kepler University are developing a new approach to mid-infrared spectroscopy that relies on photons that go undetected as they probe a sample. Utilizing spontaneous parametric down-conversion (SPDC), which usually occurs on the order of 10⁻⁹, the team generates correlated photons, employing the longer-wavelength "idler" photons as the probing mid-IR source while measuring changes via the shorter-wavelength "signal" photons. This quantum nonlinear interferometer offers significant advantages, including room-temperature operation and shot-noise-limited detection, potentially streamlining non-destructive testing applications. In this work, the team demonstrates mid-IR microscopic mapping and QFTIR spectroscopy, alongside mid-IR OCT, as promising techniques for routine, quantum-based…