Reflective terahertz time-domain spectral thickness measurement method based on evolutionary optimization algorithm

Abstract

The invention discloses a reflective terahertz time-domain spectral thickness measurement method based on an evolutionary optimization algorithm. A self-built all-optical excitation and receiving non-contact reflection type terahertz time-domain spectrum detection system is adopted, filtering noise reduction and Fourier transform are carried out on a reference signal and a sample signal, a MATLABcross-correlation function is utilized to obtain an intrinsic phase shift, and a coating sample refractive index spectrum and an extinction coefficient spectrum in a terahertz frequency band range areobtained. The constructed terahertz wave and medium interaction theoretical model becomes more accurate, full-spectrum fitting is carried out on a theoretical reflection terahertz time-domain waveform and an experimental sample signal by utilizing an evolutionary optimization algorithm, and the number of iterations or convergence precision is determined; according to the method, the constructed terahertz wave and medium interaction theoretical model is more accurate in a mode close to reality, measurement errors caused by factors such as inherent phase shift errors and metal substrate complexrefractive indexes changing along with frequency spectra are avoided, echo pulse detection precision is improved, coating detection depth resolution is enhanced, and thickness detection is achieved.

Description

technical field [0001] The invention relates to the technical field of terahertz time-domain spectrum detection, in particular to a reflective terahertz time-domain spectrum thickness measurement method based on an evolutionary optimization algorithm. Background technique [0002] With the vigorous development of aviation industry technology, protective coatings are key components of these large-scale equipment or high-end equipment, and their health status directly affects the integrity, safety and service life of the overall structure, and at the same time determines the corrosion resistance and anti-corrosion properties of components. oxidation capacity. Thickness is an important evaluation index to characterize the quality and integrity of coatings. Accurate measurement of coating thickness is of great significance to maintain the function of aerospace composite protective coatings and ensure the quality of substrate materials. Due to the complex preparation process, sp...

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Problems solved by technology

Terahertz reflective time-domain spectroscopy system can measure the minimum thickness value d according to the single-point coating thickness extraction model min is half of the coherence length of the terahertz pulse in the dielectric layer, when the thickness of the dielectric layer is less than d min When (for thin coatings), the terahertz echo pulses overlap in the time domain, and because of the discontinuity of the refractive index between the interfaces caused by the chemical properties and structural differences of the medium layer, the terahertz pulses will have multiple reflections. When the single-point coating thickness extraction model is no longer applicable

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