Quantum-inspired terahertz spectroscopy with visible photons

Terahertz technology offers solutions in nondestructive testing and spectroscopy for many scientific industrial applications. While direct detection of photons this frequency range is difficult to achieve, quantum optics provides a highly attractive alternative: it enables the characterization materials hardly accessible spectral ranges by measuring easily detectable different range. Here we report on application principle terahertz spectroscopy, absorption features chemicals at sub-terahertz frequencies detecting visible photons. To generate needed correlated signal-idler photon pairs, periodically poled lithium niobate crystal 660 nm continuous-wave pump source are used. After propagating through single-crystal nonlinear interferometer, filtered narrowband volume Bragg gratings. An uncooled CMOS camera detects frequency-angular spectra remaining signal reveals terahertz-spectral information. Neither cooled detectors nor expensive pulsed lasers coherent required.