Low-Noise Infrared Spectroscopy via Tunable Frequency Upconversion at Single-Photon Level

Infrared spectroscopy plays a significant role in applied science as well as in fundamental science. Lots of research works have been focused on the infrared spectrum measurement over the last few decades. Recently, the Fourier transfer spectrometer based on frequency comb lasers arouses a great deal of research interest for its fast and accurate measurement. However, the sensitivity of infrared spectrometers still requires improvement. Here, we demonstrate an efficient infrared spectrometer with high detection sensitivity at single-photon level using a wavelength tunable frequency upconversion detection technique with synchronized laser sources. Because of the high conversion efficiency and low background noise, the infrared transmittance spectrum of hydrogen sulfide gas was successfully recovered by this spectrometer at single-photon level. This kind of spectrometers could be potentially applied in gas monitoring and remote spectrum analysis.