太赫兹时域光谱仪光谱范围和信噪比校准技术

Calibration technology for spectral range and signal-to-noise ratio of terahertz time-domain spectrometer

光谱范围和信噪比是评价太赫兹时域光谱仪性能的重要参数。为了解决太赫兹时域光谱仪光谱范围和信噪比的校准问题,介绍了太赫兹时域光谱仪的构成及原理,比较了目前常用的光谱范围和时域信噪比校准方法的优缺点,并优选其中一种方法,设计了太赫兹时域频域信噪比参数校准方法。以空测时频域信号幅值最大值的1/M对应的频率范围作为光谱范围,研究了M取值对光谱范围的影响。M值越大,则光谱范围越宽。当M值≥50时,光谱范围变化不大。对空测时域信号的信号和噪声进行定义,并计算出时域信噪比。以空测时的频域功率谱作为信号,以金属板遮挡光路时的频域功率谱作为噪声,从而计算出频域信噪比。进行了光谱范围和信噪比校准实验,采用对照法研究了湿度变化对太赫兹时域光谱仪测量范围和信噪比参数的影响。当相对湿度≤50%时,对光谱范围和时域信噪比影响不大;当相对湿度>50%时,因为空气中水蒸气对于太赫兹的吸收急剧增加,光谱范围和信噪比急剧缩小。

Spectral range and signal-to-noise ratio(SNR)are important parameters to evaluate the performance of terahertz time-domain spectrometer(TDS).To solve the calibration problems of spectral range and SNR for TDS,the composition and principle of TDS were introduced.The advantages and disadvantages of the commonly-used calibration methods were compared,and one of the methods was selected to design the parameter calibration method of terahertz time-domain frequency-domain SNR.The frequency range corresponding to 1/M of the maximum amplitude of signal in the frequency domain was taken as the spectral range,and the influence of M value on spectral range was studied.The larger the M value,the wider the spectral range.When M value was greater than or equal to 50,the spectral range changed little.The signal and noise of the timedomain signal were defined,and the time-domain SNR was calculated.Using the frequency-domain power spectrum of air as the signal,the frequency-domain power spectrum in the light path covered by matal plate was taken as the noise,and the frequency-domain SNR was calculated.The calibration experiments of spectral range and SNR were carried out,and the influence of humidity variation on spectral range and SNR parameters of TDS was studied by contrast method.When the relative humidity was less than or equal to 50%,the influence on spectral range and time-domain SNR was not obvious.When the relative humidity was greater than 50%,because the absorption of water vapor increased sharply,the spectral range and SNR decreased sharply.