A method for enhancing terahertz absorption spectra of materials

Abstract

This invention discloses a method for enhancing the terahertz absorption spectrum of materials. The method uses a terahertz time-domain spectroscopy system to measure the material spectrum, calculates the material's transfer function, amplitude, and phase using the acquired reference signal and sample signal, fits the material's absorption spectrum by constructing a multi-Gaussian function model, and enhances the absorption spectrum through a coefficient enhancement factor. This strengthens the ability to identify minute differences in the terahertz spectrum and improves the ability of terahertz spectroscopy to distinguish substances with similar properties, similar compositions, and trace amounts.

Description

Technical Field

[0001] This invention belongs to the field of terahertz nondestructive testing, specifically relating to a terahertz absorption spectroscopy enhancement method. Background Technology

[0002] Terahertz spectroscopy, as an emerging spectroscopic technique, is widely used in non-destructive testing and material identification due to its advantages such as high signal-to-noise ratio, strong penetration, fingerprint spectral characteristics, and low photon energy. In particular, some polar, non-polar, and macromolecular materials exhibit responses in the terahertz band. By acquiring the absorption spectra of these materials and identifying their unique spectral characteristics, qualitative and quantitative analysis of substances can be achieved, enabling its wide application in fields such as biology, medicine, coal mining, and security.

[0003] Traditional methods acquire terahertz signals with and without samples, and directly obtain the absorption spectrum of materials using analytical methods. This allows for accurate qualitative and quantitative analysis of materials with significant spectral characteristics. However, for materials with similar properties or small differences in composition, as well as trace substances, the differences in spectral characteristics are not significant enough, which poses difficulties for qualitative and quantitative analysis. Summary of the Invention

[0004] The purpose of this invention is to provide a method for enhancing the terahertz absorption spectrum of materials. By constructing a multi-Gaussian function fitting model to fit the absorption spectrum of the material, and by using a coefficient enhancement factor, the absorption spectrum is enhanced, thereby strengthening the ability to identify minute differences in the terahertz spectrum and improving the ability of terahertz spectroscopy to distinguish substances with similar properties, similar compositions, and trace amounts.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for enhancing the terahertz absorption spectrum of a material includes the following steps:

[0007] Step 1: Measure the material spectrum using a terahertz time-domain spectroscopy system: First, acquire the terahertz time-domain spectral signal E in the sample-free state. ref Place the material and collect the terahertz time-domain spectral signal E in the sample state. sample ;

[0008] Step 2: Calculate the absorption spectrum of the material: Using the reference signal and sample signal acquired in Step 1, calculate the material's transfer function H(ω), as well as its amplitude ρ(ω) and phase.

[0009] Step 3: Construct a multi-Gaussian function model to fit and enhance the material's absorption spectrum.

[0010] Furthermore, the terahertz time-domain spectroscopy system used in step one is a terahertz transmission measurement device, which includes a terahertz transmitter, a terahertz receiver, and a pair of HDPE lenses. The terahertz transmitter generates terahertz waves that are focused by the HDPE and penetrate the material sample before being received by the terahertz receiver.

[0011] Furthermore, step two includes:

[0012] 2.1) Use Fast Fourier Transform to convert the terahertz time-domain spectral signal E obtained in step one into a terahertz time-domain spectral signal. ref and terahertz time-domain spectral signal E sample Converted into frequency domain signal E respectively ref (ω) and frequency domain signal E sample (ω), where ω is the angular frequency;

[0013] 2.2) Calculate the transfer function H(ω), its magnitude ρ(ω), and its phase. The calculation formula is as follows:

[0014]

[0015] ρ(ω)=|H(ω)|

[0016]

[0017] In the formula, i is the imaginary unit; phase(H(ω)) is the phase solution function of the transfer function H(ω); imag(H(ω)) is the imaginary part of the transfer function; and real(H(ω)) is the real part of the transfer function.

[0018] 2.3) Calculate the absorption spectrum α(ω) of material sample 2 using the following formula:

[0019]

[0020]

[0021] Where ω is the angular frequency; d is the material thickness; n(ω) is the refractive index of the material; and c is the propagation speed of electromagnetic waves in a vacuum.

[0022] Furthermore, step two includes:

[0023] 3.1) Based on the number n of characteristic absorption peaks in the material, construct a model G(ω) containing n Gaussian functions, with the following formula:

[0024]

[0025] Where, ω′ i Let a be the frequency of the i-th characteristic absorption peak. iLet b be the amplitude of the i-th characteristic absorption peak. i The width of the i-th characteristic absorption peak;

[0026] 3.2) The absorption spectrum α(ω) is fitted to the model constructed in step 3.1) using the least squares method to obtain the parameter ω′ of each characteristic absorption peak. i a i and b i ;

[0027] 3.3) For each characteristic absorption peak parameter a i and parameter b i Make adjustments and input them into the model G(ω) constructed in step 3.1). The adjustment method is as follows:

[0028] a′ i =k a ·a i

[0029] b′ i =k b ·b i

[0030] Where, k a k is the amplitude adjustment factor. b a′ is the width adjustment factor. i and b′ i These are the adjusted characteristic absorption peak parameters.

[0031] Furthermore, in step 3.3), k is increased. a To enhance the amplitude of the characteristic absorption peak and reduce k b A smaller characteristic absorption peak width is obtained, thereby enhancing the absorption spectrum of the material and enabling high-precision identification of weak or difficult-to-distinguish characteristic absorption peaks.

[0032] The present invention has the following beneficial effects:

[0033] This invention provides a method for enhancing the terahertz absorption spectrum of materials. By constructing a multi-Gaussian function fitting model to fit the absorption spectrum of the material, and using a coefficient enhancement factor to enhance the absorption spectrum, this method can enhance materials with similar properties or small differences in composition, as well as trace substances with minute differences, thereby improving the accurate identification of the material's absorption characteristics. This method can be applied to the analysis of pharmaceutical components and the detection of trace explosives and narcotics. Attached Figure Description

[0034] Figure 1 Flowchart of a method for enhancing terahertz absorption spectroscopy in materials;

[0035] Figure 2 Schematic diagram of a terahertz absorption spectroscopy detection system for materials; Detailed Implementation

[0036] The present invention will be further described in detail below through specific embodiments. The following embodiments are merely descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0037] This embodiment describes a method for enhancing the terahertz absorption spectrum of materials, using a terahertz transmission measurement device such as... Figure 2 As shown, it includes a terahertz transmitter 1, a terahertz receiver 3, and a pair of HDPE lenses. The terahertz transmitter 1 generates terahertz waves, which are focused by the HDPE and penetrate the sample 2 before being received by the terahertz receiver 3.

[0038] like Figure 1 As shown, the method for enhancing the terahertz absorption spectrum of a material in this embodiment includes the following steps:

[0039] Step 1: Measure the material spectrum using a terahertz time-domain spectroscopy system.

[0040] 1.1) First, acquire the terahertz time-domain spectral signal E when there is no sample. ref As a reference signal;

[0041] 1.2) Then, material sample 2 is placed between terahertz transmitter 1 and terahertz receiver 3, and the terahertz time-domain spectral signal E is acquired when material sample 2 is present. sample As a sample signal.

[0042] This embodiment uses, as follows Figure 2 The terahertz transmission measurement device shown includes a terahertz transmitter 1, a terahertz receiver 3, and a pair of HDPE lenses. The terahertz transmitter 1 generates terahertz waves, which are focused by the HDPE and penetrate the material sample 2 before being received by the terahertz receiver 3.

[0043] Step 2: Calculate the absorption spectrum of the material: Using the reference signal and sample signal acquired in Step 1, calculate the material's transfer function H(ω), as well as its amplitude ρ(ω) and phase.

[0044] 2.1) Use Fast Fourier Transform to convert the terahertz time-domain spectral signal E obtained in step one into a terahertz time-domain spectral signal. ref and terahertz time-domain spectral signal E sample Converted into frequency domain signal E respectively ref (ω) and frequency domain signal E sample (ω), where ω is the angular frequency;

[0045] 2.2) Calculate the transfer function H(ω), its magnitude ρ(ω), and its phase. The calculation formula is as follows:

[0046]

[0047] ρ(ω)=|H(ω)

[0048]

[0049] In the formula, i is the imaginary unit; phase(H(ω)) is the transfer function. H The phase function for H(ω) is imag(H(ω)), which is the imaginary part of the transfer function, and real(H(ω)) is the real part of the transfer function.

[0050] 2.3) Calculate the absorption spectrum α(ω) of material sample 2 using the following formula:

[0051]

[0052]

[0053] Where ω is the angular frequency; d is the material thickness; n(ω) is the refractive index of the material; and c is the propagation speed of electromagnetic waves in a vacuum.

[0054] Step 3: Construct a multi-Gaussian function model to fit and enhance the material's absorption spectrum:

[0055] 3.1) Based on the number n of characteristic absorption peaks in the material, construct a model G(ω) containing n Gaussian functions, with the following formula:

[0056]

[0057] Where, ω′ i Let a be the frequency of the i-th characteristic absorption peak. i Let b be the amplitude of the i-th characteristic absorption peak. i The width of the i-th characteristic absorption peak;

[0058] 3.2) The absorption spectrum α(ω) is fitted to the model constructed in step 3.1) using the least squares method to obtain the parameter ω′ of each characteristic absorption peak. i a i and b i ;

[0059] 3.3) For each characteristic absorption peak parameter a i and parameter b i Make adjustments and input them into the model G(ω) constructed in 3.1. The adjustment method is as follows:

[0060] a′ i =k a ·a i

[0061] b′ i =k b ·b i

[0062] Where, k a k is the amplitude adjustment factor. b a′ is the width adjustment factor. i and b′ i These are the adjusted characteristic absorption peak parameters. Increasing k a It can enhance the amplitude of the characteristic absorption peak and reduce k. b It can obtain a smaller characteristic absorption peak width, thereby enhancing the absorption spectrum of the material and enabling high-precision identification of weak or difficult-to-distinguish characteristic absorption peaks.

Claims

1. A method of enhancing terahertz absorption spectroscopy of a material, the method comprising: The method comprises the following steps: Step 1: Measure the material spectrum using a terahertz time-domain spectroscopy system: First, acquire the terahertz time-domain spectral signal E in the sample-free state. ref Place the material and collect the terahertz time-domain spectral signal E in the sample state. sample ; Step two, calculate the absorption spectrum of the material: use the reference signal and sample signal collected in step one to calculate the transfer function H(ω) of the material and the amplitude p(ω) and phase of the transfer function The step two includes: 2.1) using fast Fourier transform to transform the terahertz time-domain spectrum signal E ref and the terahertz time-domain spectrum signal E sample into frequency domain signals E ref (ω) and E sample (ω), respectively, wherein ω is an angular frequency; 2.2) Calculate the transfer function H(ω) and the magnitude p(ω) and phase of the transfer function The calculation formula is as follows: P(ω) = |H(ω)| In the formula, i is an imaginary unit; phase(H(ω)) is a phase solving function of the transfer function H(ω); imag(H(ω)) is an imaginary part of the transfer function, and real(H(ω)) is a real part of the transfer function; 2.3) calculating the absorption spectrum a(ω) of the material sample 2, and the calculation formula is as follows: Wherein, ω is an angular frequency; d is a material thickness; n(ω) is a material refractive index; and c is a propagation speed of an electromagnetic wave in vacuum; Step three, constructing a multi-Gaussian function model to fit and enhance the material absorption spectrum; the step three comprises: 3.1) constructing a model G(ω) containing n Gaussian functions according to the number n of characteristic absorption peaks of the material, and the formula is as follows: where ω' = ω - ω0 i is the frequency at which the i-th characteristic absorption peak is located, a i is the amplitude of the i-th characteristic absorption peak, b i is the width of the i-th characteristic absorption peak; 3.2) fitting the model constructed in step 3.1) to the absorption spectrum a(ω) using a least squares method to obtain the parameters ω' of each characteristic absorption peak i , a i and b i ; 3.3) For each characteristic absorption peak parameter a i and parameter b i Make adjustments and input them into the model G(ω) constructed in step 3.1). The adjustment method is as follows: a′ i = k a • a i b′ i = k b • b i wherein k a is an amplitude adjustment factor, k b is a width adjustment factor, a′ i and b′ i are the adjusted characteristic absorption peak parameters, respectively.

2. A method of enhancing terahertz absorption spectroscopy of a material as claimed in claim 1, wherein, The terahertz time-domain spectroscopy system used in the step one is a terahertz transmission type measuring device, which comprises a terahertz emitter, a terahertz receiver and a pair of HDPE lenses. The terahertz emitter generates terahertz waves which are focused by the HDPE and then penetrate the material sample and are received by the terahertz receiver.

3. The method for enhancing the terahertz absorption spectrum of a material as described in claim 1, characterized in that, In step 3.3), k is increased a The enhancement of the characteristic absorption peak amplitude is realized by reducing k b The characteristic absorption peak width is smaller, and the enhancement of the material absorption spectrum is realized, and the weak characteristic absorption peak or the difficult-to-distinguish characteristic absorption peak is identified with high precision.

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