Low-noise Synchronized Mid-Infrared Upconversion Spectrometer with a Large Spectral Coverage

Mid-infrared (MIR) frequency upconversion presents a powerful tool for MIR photon detection at room temperature. However, the introduction of strong pump light will exacerbate the limitations of upconverted thermal radiation and upconverted parametric fluorescence on detectability in broadband MIR frequency upconversion. Here, a broadband synchronized MIR upconversion spectrometer system based on a step-chirped poled LiNbO3 crystal is demonstrated. This system is integrated with spontaneous parametric downconversion (SPDC) and sum-frequency generation (SFG) to form a broadband MIR light generation and synchronous pulsed upconversion, which are simultaneously driven by the same pulsed pump laser. The spectral coverage is close to 1.4 μm from 2450 to 3850 nm and the resolution of the system is about 4 cm−1 after deconvolution, as confirmed by a Fourier transform infrared spectrometer. In conjunction with synchronous pumping-based temporal gating, the system noise is suppressed to less than 10 counts per second per nm. This broadband synchronized SPDC–SFG configuration can be extended to different infrared wavelengths for low-noise broadband spectroscopic measurement.