New method for mid-infrared spectroscopy at room temperature using non-linear optics in photon-counting regime

We propose a new spectroscopy technique in the mid-infrared (MIR) domain without any cryogenic system. The MIR field emitted by the source is shifted to the near-infrared using sum-frequency generation in a Periodically Poled Lithium Niobate ridge waveguide, and is then detected in the photon-counting regime using a low-noise SiAPD detector. The non-linear process is powered by a continuously tunable pump laser. We present here an experimental proof-of-concept, where the light emitted by a thermal source in the 3-4µm band is spectrally modulated using a Michelson interferometer. By continuously tuning the pump laser wavelength between 1058 nm and 1078 nm, the MIR spectrum is reconstructed, and the imposed spectral modulation period is retrieved successfully with a relative error of less than 5%.