High‐Speed Mid‐Infrared Single‐Photon Upconversion Spectrometer

Abstract

Sensitive and fast mid‐infrared (MIR) spectroscopy is highly attractive in a variety of applications including astronomical observation, pharmaceutical synthesis, and environmental monitoring. However, the performance of conventional MIR spectrometers has long been hindered by the limited sensitivity of narrow‐bandgap detectors and/or the deficient brightness of broadband light sources. Here, an ultra‐sensitive and broadband MIR upconversion spectrometer, which integrates a supercontinuum source covering 1.5–4.2 m based on a silicon nitride nanophotonic waveguide, is devised and integrated. High‐efficiency and low‐noise nonlinear frequency upconversion is realized based on coincidence pulsed pumping with spectro‐temporal optimization, which enables leverage of silicon detectors for facilitating MIR single‐photon spectroscopy at 0.2 photons/nm/pulse. Furthermore, the upconversion‐based array spectrometer is manifested with high‐speed spectral acquisition rates beyond 200 kHz, which is about tenfold faster than the state‐of‐the‐art scan rates for FTIR‐based spectrometers at a comparable spectral resolution. The achieved features of broadband spectral coverage, single‐photon sensitivity, and sub‐MHz refreshing rate might open up new possibilities for infrared transient spectral measurements in combustion analysis, high‐throughput sorting, and reaction tracking, among others.

Wide-field mid-infrared hyperspectral imaging beyond video rate

“…The pump bandwidth will result in a resolution degradation due to the spectral convolution deformation. It is thus imperative to devise a narrow-band pump for improving the spectral correspondence 32 .

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“…The pump power is boosted to about 600 mW, and the spectral width of the amplified pulse is kept below 0.2 nm with the help of a large-mode-area fiber amplifier. The spectro-temporal engineering of the involved synchronous pulses is essential to facilitate high-fidelity spectral mapping in a high-efficiency and low-noise fashion 32 , 44 . Detailed description of the laser sources for the coincidence-pumping nonlinear upconversion is presented in Methods.…”

“…In this approach, the MIR information is typically transferred to the visible or near-infrared replica, where a sensitive and fast detection can be realized by leveraging high-performance large-bandgap sensors 24 . Such upconversion configuration has led to superior room-temperature MIR imaging performances with single-photon sensitivity 25 , 30 and sub-megahertz frame rate 31 , 32 based on high-definition silicon cameras. So far, there have been various schemes proposed to implement the MIR hyperspectral upconversion imaging 24 .…”

Single‐Photon Time‐Stretch Infrared Spectroscopy

“…[ 9–11 ] Indeed, typical MIR detectors are facing limitations in high dark current, slow response time, and low operation temperature, thus struggling to implement sensitive and fast MIR spectroscopy. [ 12,13 ] In addition, scanning‐free MIR spectrograph usually requires focal plane arrays, where the spectral resolution is severely restricted by the low pixel density. [ 9 ] Recently, superconducting nanowire detectors have been integrated to implement broadband single‐photon spectrometers, [ 14–16 ] albeit with limited operation wavelengths below 2 µm and additional system complexity in cryogenic cooling.…”

“…One common way is based on frequency upconversion of the MIR photons through a high‐efficiency and low‐noise parametric nonlinear conversion, which allows for demonstrating broadband MIR spectrometers at single‐photon sensitivity [ 18–21 ] or kHz‐above frame rates. [ 13,22,23 ] Another promising approach resorts to quantum interferometry of spectrally‐entangled photons from spontaneous parametric down conversion (SPDC), [ 24,25 ] which features intrinsic single‐photon‐level sensitivity. In both methods, the involved spectral analysis is often conducted in the spatial domain based on a monochromator [ 19,20 ] or a spectrograph.…”