Fourier Transform Near-Infrared Spectral System Based on Laser-Driven Plasma Light Source
WANG Yue1, 3, 4, CHEN Nan1, 2, 3, 4, WANG Bo-yu1, 5, LIU Tao1, 3, 4*, XIA Yang1, 2, 3, 4*
1. Institute of Microelectronics of the Chinese Academy of Sciences, Beijing 100190, China
2. University of Chinese Academy of Sciences, Beijing 100049, China
3. Beijing Research Center of Engineering and Technology of Instrument and Equipment for Microelectronics Fabrication, Beijing
100029, China
4. Beijing Key Laboratory of IC Test Technology, Beijing 100089, China
5. School of Graduate, Beijing Jiaotong University, Beijing 100044, China
Abstract：As a commonly used scientific research-grade near-infrared spectral detection instrument, the near-infrared Fourier transformation spectrometer is widely used in various scientific research fields. The current near-infrared spectrometer focuses on improving spectral resolution and pays less attention to the improvement of the spectral signal-to-noise ratio. The spectral signal-to-noise ratio directly affects the accuracy of spectral line index measurement, the higher the spectral signal-to-noise ratio. The higher the accuracy of spectral line index measurement, the more conducive to the fine spectral comparison of trace substances. Therefore, it is necessary to improve the spectral signal-to-noise ratio of the spectrometer. Compared with commonly used tungsten light sources, laser-driven plasma light sources (LDLS) not only have the advantages of high light intensity in near-infrared regions but also their unique high-frequency modulation output signal can be well suppressed by the background signal on the interference spectrum after modulation and deconstruction by the lock-phase amplifier. The combination of high brightness and radiation modulation has significantly improved the spectral signal-to-noise ratio of the near-infrared Fourier transformation spectral system with LDLS as the light source. For the above reasons, this paper proposes to use the new laser-driven plasma light source as the spectral signal output source of the near-infrared Fourier transformation spectral system, and with the modulation ability of tungsten light source set up by the near-infrared Fourier transformation spectral system to carry out a comparative experiment of signal-to-noise ratio. Firstly, the tungsten light source is used by chopper high-frequency modulation and then de-adjusted by the lock-phase amplifier, the integration time of the lock-phase amplifier is optimized, and the interference spectral signal-to-noise ratio is calculated by using the signal-to-noise ratio evaluation method given in the text. The signal-to-noise ratio is compared separately, the integral time is 0.5, 1, 5, 10 and 20 ms, respectively. Interference spectrum signal-to-noise ratio and symmetry, and the optimal integration time of the phase-lock amplifier in subsequent systems are determined to be 5ms. The interference spectrum signal-to-noise ratio of tungsten light sources in this state is calculated to be about 90∶1. The system built by using laser-driven plasma light source instead of a tungsten light source and chopper is used to build the system of the light source at the optimum integration time. The results of the comparative evaluation of interference spectrum signal-to-noise ratio of traditional light source systems show that the interference spectrum signal-to-noise ratio of laser-driven plasma light sources is 111 times higher than that of conventional tungsten light sources. The results show that the near-infrared Fourier transformation spectral system, constructed by the light source, has a peak error of 0.5 nm
Key words：Fourier transform spectrometer; Laser plasma; Near infrared spectroscopy; Lock-in amplifier; Signal-to-noise ratio
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