Sensing techniques with undetected photons in the mid-infrared

Mid-infrared (MIR) sensing is of enormous interest in many industries due to its ability to identify samples through their MIR absorption spectrum, revealing highly specific molecular information. However, direct MIR sensing is limited by the inefficiency, noise, and high costs of current MIR detection technologies, along with the complexity of MIR sources. Our research focuses on overcoming these challenges through “sensing with undetected photons”. This technique uses nonlinear interferometry and strongly non-degenerate photon pairs to separate the probe and detection wavelengths, allowing MIR samples to be analysed with silicon-based detectors. This greatly reduces the size, weight, power, and cost of MIR sensing. We demonstrate the application of this principle to spectroscopy, optical coherence tomography, and wide-field microscopy, opening up a wide range of potential applications. Additionally, we present our progress towards industrial applications like environmental monitoring of microplastics and non-destructive testing of ceramics, marking a promising future for this technology.