Mid-infrared (MIR) spectroscopy is an effective tool for material characterization and identification, and has a wide range of applications in the fields of biology, medicine, materials and environment. Especially in many low illumination applications, such as long-distance pollution monitoring, non-destructive cultural relics identification and low phototoxicity cell observation, there is an urgent need for highly sensitive mid-infrared spectroscopic detection technology. However, narrow bandgap infrared detectors are usually used in traditional mid-infrared spectrometers, which are affected by endowment dark current and ambient thermal noise, resulting in limited detection sensitivity. Therefore, it is challenging to realize ultrasensitive mid-infrared spectroscopic detection approaching the single-photon level at room temperature.
In recent years, the single-pixel computational spectroscopy technique, with the help of spatial light modulation and single-pixel detectors, can realize high-throughput measurements with wavelength multiplexing, and reconstruct the spectral information to be measured by correlation solving. However, single-pixel computational spectroscopy at the single-photon level has long been limited to the visible/near-infrared band due to the lack of highly sensitive mid-infrared detectors. In addition, another constraint in realizing mid-infrared single-pixel spectroscopy is the lack of high-fidelity spatial modulation devices. Conventional spatial light modulators based on liquid crystals or digital micromirror elements have a limited range of operating wavelengths, and the modulation performance is inevitably affected by long-wavelength diffraction effects. For this reason, the research team of Kun Huang and Prof. Heping Zeng innovatively combined the frequency upconversion detection technology and wavelength encoding computational spectroscopy technology to break through the difficulties of high-sensitivity detection and high-resolution modulation in the mid-infrared band, and realized a single-pixel computational spectrometer in the mid-infrared at the single-photon level.
Using the chirped pulse pumping technique, the research team of Kun Huang and Prof. Heping Zeng precisely converted the spectral information of the broadband covering 3.1-3.9 μm to the near-infrared band, and utilized the high-performance spatial light modulator and silicon-based detector in this band for spectral modulation and photon detection to achieve a spectral resolution of 0.5 cm-1 with a single-photon illumination as low as 0.01 photons/nm/pulse. spectral resolution of 0.5 cm-1 at a single photon illumination as low as 0.01 photons/nm/pulse, which achieves an order of magnitude improvement in detection sensitivity compared to previous records. Moreover, the data acquisition time was dramatically reduced by 95% in combination with the compressed sensing algorithm, which is especially critical for improving the rate of microlight spectral analysis under fewer photons. In addition, the flexible encoding capability of the spatial light modulator enables the researchers to measure specific spectral regions to further improve the spectral acquisition efficiency; or to conduct more fine sampling in the region of interest, providing an effective way to balance high resolution and broad spectral coverage. The research team realized for the first time a single-pixel computational spectrometer with single-photon detection sensitivity in the mid-infrared, combining the dual advantages of upconversion detection and single-pixel spectroscopy, getting rid of the dependence on large surface array detector devices and mechanical scanning components, and using single-pixel photon detectors to achieve sub-wavelength spectral resolution over a wide spectral coverage range. It is worth mentioning that this technology can be extended to the long-wave infrared or terahertz region to meet the urgent need for high sensitivity and high resolution spectral measurements in this spectral band. In the future, the integration of multi-dimensional computational imaging technology can also obtain multi-degree-of-freedom information such as spatial, polarization and phase of the samples, providing a new type of analysis means for the fields of materials, chemistry, medicine, biology and so on.
The related results were published in Laser & Photonics Reviews, and were co-funded by the Ministry of Science and Technology, Funding Committee, Shanghai Municipal Science and Technology Commission, Chongqing Science and Technology Bureau and East China Normal University. This work was also supported by the groups of Prof. Hairun Guo from Shanghai University and Associate Prof. Yan Liang from Shanghai Institute of Technology.
Figure. (a) Conceptual diagram of mid-infrared single-photon computational spectroscopy; (b) mid-infrared spectral coverage of 3.1-3.9 μm; (c) spectral resolution of 0.5 cm-1; (d) acquisition time can be reduced by 95%; and (e) detection sensitivity up to 0.01 photons/nm/pulse.
Link to paper: Mid-Infrared Single-Photon Compressive Spectroscopy
