[Study on the Measurement and Optimization of Soybean Oil Optical Spectrum in THz Range]

Area of Science:

• Physics
• Spectroscopy
• Materials Science

Background:

• Terahertz time-domain spectroscopy (THz-TDS) is a powerful technique for spectral measurements using femtosecond lasers.
• THz waves offer unique properties for nondestructive testing across various applications.
• A common challenge in THz-TDS is spurious oscillations in optical parameter calculations for liquids, caused by the Fabry-Perot effect.

Purpose of the Study:

• To develop and present a novel signal processing technique to mitigate spurious oscillations in THz-TDS.
• To improve the accuracy and frequency resolution of optical parameter measurements for liquid samples.
• To effectively remove echo signals that cause oscillations in THz spectra.

Main Methods:

• An improved de-convolution algorithm based on a traditional optical parameter calculation model was developed.
• The algorithm accounts for nonlinear absorption of THz waves by samples and optical components.
• The method analyzes THz time-domain traces as a convolution of primary peaks, delta functions, and nonlinear transfer functions.

Main Results:

• The improved algorithm effectively removes or reduces spurious oscillations caused by echo signals in THz spectra.
• Accurate transmission spectrum of soybean oil (0.2–2.0 THz) was measured using THz-TDS.
• Frequency resolution for soybean oil improved from 50 GHz to less than 10 GHz compared to traditional methods.

Conclusions:

• The developed algorithm effectively eliminates frequency oscillations caused by echoes in THz-TDS.
• This method is applicable to various liquid measurements in the THz range and is independent of the tested object.
• The study provides a robust approach for obtaining high-frequency resolution and accurate optical parameters from THz-TDS data.