基于激光驱动等离子体光源的近红外傅里叶变换光谱系统

Fourier Transform Near-Infrared Spectral System Based on Laser-Driven Plasma Light Source

近红外傅里叶变换光谱仪作为一种常用的科研级近红外光谱检测仪器,广泛应用于各个科研领域。目前的近红外光谱仪着重于光谱分辨率方面的提升,在光谱信噪比提升方面关注较少。光谱信噪比直接影响光谱线指数测量精度的优劣,光谱信噪比越高,光谱线指数测量精度越高,越有利于对微量物质进行精细光谱比对。因此,提升光谱仪的光谱信噪比是十分必要的。对比常用的钨灯光源,激光驱动等离子体光源(LDLS)不仅在近红外区域具有高光照强度的优点,而且其独特的高频调制输出信号在经锁相放大器调制解调后能够很好的抑制背景信号对干涉光谱所带来的影响。高亮度与辐射调制的结合使得以LDLS作为光源的近红外傅里叶变换光谱系统在光谱信噪比方面获得显著提升。基于上述原因,提出利用新型激光驱动等离子体光源作为光谱信号输出源的近红外傅里叶变换光谱系统,并与含有调制能力的钨灯光源搭建的近红外傅里叶变换光谱系统进行了信噪比的比较实验。首先利用钨灯光源由斩波器高频调制再经过锁相放大器解调的方式,对锁相放大器积分时间进行优化并通过计算干涉光谱信噪比进行评估,分别对比了积分时间为0.5,1,5,10和20 ms的干涉光谱信噪比与对称度,确定后续系统中的锁相放大器最佳积分时间为5 ms,该状态下钨灯光源所实现的干涉光谱信噪比经计算约为90∶1;其次利用激光驱动等离子体光源代替钨灯光源和斩波器,在最佳积分时间下进行干涉光谱信噪比对比评估,结果表明激光驱动等离子体光源的干涉光谱信噪比与传统钨灯光源相比提升111倍;最后,利用近红外标准片对系统进行光谱测量准确性评估,结果表明利用该光源的近红外傅里叶变换光谱系统的近红外吸收峰值误差<0.5 nm,具有高光谱准确性与分辨能力。

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<near-infrared absorption and has hyperspectral accuracy and resolution.