A method for measuring water vapor terahertz absorption spectrum

Abstract

The invention provides a method for measuring the water vapor terahertz absorption spectrum. The steps include: s The water vapor THz‑TDS signal is subjected to adaptive short-time Fourier transform, and the FFT results after each adaptive adjustment are saved in the two-dimensional array Φ(k,j); according to the two-dimensional array Φ(k,j) using The frequency correction method calculates the frequency value corresponding to the absorption peak. The water vapor terahertz absorption spectrum measurement method performs an adaptive short-time Fourier transform on the water vapor THz-TDS signal, and adaptively adjusts the Gauss window width according to the number of frequency-domain absorption peaks, ensuring all spectral details including absorption peaks can be presented, if there is no absorption peak in the signal sample in the Gauss window, adaptively increase the width of the Gauss window, improve the efficiency of the algorithm to process the remaining signal samples, and reduce the amount of calculation; the frequency correction method is used to estimate the frequency of the absorption peak, which overcomes the discrete The "fence effect" in the frequency domain brought about by the Fourier transform improves the accuracy of frequency estimation.

Description

technical field [0001] The invention relates to a measurement method for terahertz absorption spectrum, in particular to a measurement method for water vapor terahertz absorption spectrum. Background technique [0002] Terahertz (THz) waves refer to electromagnetic radiation with a frequency from 0.1 THz to 10 THz. From the perspective of frequency, it is in the spectrum transition region between radio wave millimeter wave and light wave infrared; in energy, it is between electron and photon. Due to its unique physical properties, THz waves are widely used in imaging, label-free gene detection, biology, physics and chemistry, and broadband communication. In recent years, the development and maturity of femtosecond laser technology has provided an effective means for the application and research of THz waves. Since femtosecond laser technology is less affected by thermal noise and can transmit / receive detection signals within the femtosecond time window, THz time-domain spe...

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Problems solved by technology

Due to the good time-frequency resolution of wavelet transform, in theory, it is possible to analyze the details of any frequency by gradually refining the frequency domain step size. However, in practical applications, there are two reasons that will affect the time-frequency analysis effect of wavelet transform: one , if you want to analyze any frequency details, you need a very fine frequency domain step size, which will bring an unpredictable amount of calculation; second, because the THz-TDS measurement signal of water vapor has very typical non-stationary characteristics, namely The frequency jump is sudden, even wavelets that are good at edge detection are difficult to capture these sudden changes, resulting in increased ambiguity of time-frequency characteristics

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