Research of Mid-Infrared Time-Stretch Frequency Upconversion
Hyperspectral Imaging System
PENG Bo1, WEN Zhao-yang1, WEN Qi1, LIU Ting-ting1, 2*, XING Shuai3, WU Teng-fei3, YAN Ming1, 2*
1. State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
2. Chongqing Key Laboratory of Precision Optics, Chongqing Institute of East China Normal University, Chongqing 401121, China
3. AVIC Changcheng Institute of Metrology & Measurement, Beijing 100095, China
Abstract：Hyperspectral imaging is a non-contact, non-destructive detection method to analyze substances' chemical composition, physical properties, and morphology.Limited by the response speed and inherent noise of the detector,it is difficult for traditional hyperspectral imaging techniques to achieve high-speed and high signal-to-noise detection of molecular fingerprint spectra in the mid-infrared band. With the advantages of high measurement speed, high spectral resolution, and wide spectral coverage,the spectroscopy technology based on time-stretch frequency upconversion provides a reliable method for rapidlyanalyzing the type and morphology of the samples when combined with hyperspectral imaging technology. In thispaper, a mid-infrared time-stretch frequency upconversion hyperspectral imaging system was constructed. The average power of the 1 047 nm pump pulse and the 1 550 nm signal pulse generated by the same laser source is 2 W and 100 mW, respectively. Using synchronous pump technology, mid-infrared pulses were generated in one periodically poled lithium niobate crystal, and frequency upconverted into near-infrared pulses in another. This process transferred the mid-infrared molecular fingerprint spectra to the near-infrared band, which can effectively address the problem of lacking high-speed and low-noise detectors in the mid-infrared band. By tuning the operating temperature and working channels of the crystal,the detection range of the system can cover 2 700~3 900 nm, enabling the measurement of multiple samples. Combining the time-stretch method with hyperspectral imaging technology, the benzene solution's absorption spectra and spatial distribution information in a colorimetric dish were measured through point-by-point scanning. The spectral data obtained highly matched the results from a Fourier transform infrared spectrometer. Moreover, the system could perform hyperspectral imaging of a 600 μm×1 200 μm spatial region within 8 s. The acquisition time for a single pixel was 12.9 ns, and a spectral measurement speed of 77.6 MSpectra·s-1 and spectral resolution of 5.8 cm-1 was achieved. These results verified the systemhas the potential to measure the spectra and spatial distributionof liquid molecules within the spectral coverage range with highspeed and highresolution. This paper solves the problems of slow response speed, long integration time, and low signal-to-noise ratio of traditional hyperspectral methods in the mid-infrared band. It enables the spectraldetection and morphological measurement of multi-component samples with a spectral refresh rate of 107 frames per second. It could provide a new approach for imaging analysis in material and biological fields.
Key words：Mid-infrared; Time-stretch; Frequency upconversion; Hyperspectral imaging
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