Method for measuring water vapor terahertz absorption spectrum

Abstract

The invention provides a method for measuring a water vapor terahertz absorption spectrum. The method comprises steps as follows: water vapor THz-TDS signals with sampling frequency being fs are subjected to adaptive short-time Fourier transform, and an FFT result obtained after adaptive adjustment each time is stored in a two-dimensional array phi (k,j); a frequency value corresponding to each absorption peak is calculated with a frequency correction method according to the two-dimensional array phi (k,j). According to the method for measuring the water vapor terahertz absorption spectrum, the water vapor THz-TDS signals are subjected to the adaptive short-time Fourier transform, width of a Gauss window is adaptively adjusted according to the number of absorption peaks in the frequency domain, all frequency spectrum details containing the absorption peaks can be present, if no absorption peaks exist in signal samples in the Gauss window, the width of the Gauss window is adaptively increased, the efficiency of algorithm processing of residual signal samples is increased, and computation burden is reduced; absorption peak frequency is estimated with the frequency correction method,hurdle effect of frequency domain due to discrete Fourier transform is overcome, and frequency estimation precision is improved.

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...

AI Technical Summary

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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