CN112255190B - Method, system, medium and device for filtering reflected pulse interference during THz-TDS test sample - Google Patents
Method, system, medium and device for filtering reflected pulse interference during THz-TDS test sample Download PDFInfo
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Abstract
The invention provides a method, a system, a medium and a device for filtering reflected pulse interference during THz-TDS test sample, comprising the following steps: according to a conventional THz-TDS test method, obtaining a time domain signal T of a sample Sam (t) an absorbance spectrum signal a (f) of the sample; for T Sam Performing time domain analysis on the main pulse and the first-stage reflected pulse in (t) to obtain time domain delay delta t corresponding to the main pulse and the first-stage reflected pulse; performing N-point discrete Fourier transform on the A (f) to obtain an absorption spectrum interference curve S (t) with the abscissa as an optical path difference i ) And a reflected pulse signal I (t) i )＝|S(t i )/N| 2 (i=0, 1, …, N-1); bind Δt to I (t) i ) Filtering and iterating to obtain a reflected pulse filtered signal I new (t i ) The method comprises the steps of carrying out a first treatment on the surface of the Will I (t) i ) And I new (t i ) Comparing to obtain amplitude attenuation coefficient a of corresponding filter band i ＝[I new (t i )/I(t i )] 1/2 Obtaining the discrete Fourier transform S after filtering and correction new (t i ) The method comprises the steps of carrying out a first treatment on the surface of the For S new (t i ) Performing inverse discrete Fourier transform to obtain an absorption spectrum after interference filtering: a is that new (f)＝IFFT[S new (t i )]. According to the invention, the prior acquisition of sample dispersion information or the accurate time domain position of the reflected pulse signal is not needed, and the efficient filtering of the absorption spectrum reflection peak interference fringes is realized.
Description
Technical Field
The invention relates to the technical field of terahertz, in particular to a method, a system, a medium and a device for filtering reflected pulse interference during THz-TDS test of a sample.
Background
Terahertz time-domain spectroscopy (TDS) is an emerging substance detection means that acquires broad-spectrum radiation covering several terahertz (THz) ranges in the frequency domain by generating a narrow pulse signal with a duration on the order of several picoseconds (ps) in the time domain, and by Fast Fourier Transform (FFT) in the time-domain frequency domain. The signals generated and detected by the method have coherent measurement capability, and can simultaneously acquire high-sensitivity substance absorption spectrum and time-resolved phase information, so that more abundant spectrum data of the detected substance can be acquired. The terahertz time-domain spectroscopy (THz-TDS) technology is used for carrying out spectral measurement on substances in different forms to find that the phonon frequency of condensed substances and the vibration spectrum of macromolecules have a plurality of characteristic peaks in the THz wave band, carriers in liquid have very sensitive response to THz radiation, in addition, the terahertz wave band has characteristic response to low-frequency collective vibration in molecules of a test substance, weak interaction hydrogen bonds and van der Waals force extension among molecules, bending of skeleton vibration configuration of macromolecules, rotation and vibration transition of dipoles, low-frequency absorption frequency of crystal lattices in crystals, phonon vibration modes and the like. A large number of organic macromolecule groups show obvious and unique absorption and dispersion characteristics in a terahertz wave band, corresponding molecular structure information, spectral fingerprint absorption, chemical component content and the like can be obtained through testing the terahertz spectrum of a substance, and the terahertz wave band is a powerful tool for researching the properties of biochemical macromolecule organic configuration, structure and the like.
The THz-TDS is utilized to detect terahertz characteristic spectrum of substances, a transmission type measurement mode is generally adopted, and before measurement, a sample to be detected is ground and pressed into a sheet, so that a sample with standard size and thickness is formed. The input signal power of the measurement mode is larger, and the constraint size of the focusing light spot is smaller, so that the terahertz wave band absorption spectrum of the substance with higher signal-to-noise ratio and accuracy can be obtained. However, the terahertz wave beam forms multiple reflections between the two surfaces of the sample wafer and is overlapped with the real main pulse signal of the transmitted light beam due to the fact that the surface of the sample wafer is flat. The superimposed TDS signal may exhibit reflected pulse signals in the time domain signal and significant interference fringes in the frequency domain and absorption spectrum signals. If larger interference exists in the absorption spectrum, misjudgment of absorption peaks can be caused, waveforms of real absorption peaks can be changed, and even weaker absorption peaks are submerged, so that inaccuracy of terahertz spectrum testing of substances is caused.
For filtering out reflected pulses in the TDS transmission signal of a substance, corresponding data processing optimization work has been carried out in literature. However, these operations focus on how to filter the reflected pulse signal in the time domain, in order to ensure the accuracy of the filtering effect, it is generally required that the reflected pulse signal has higher similarity to the main pulse signal, and that the reflected pulse signal and the main pulse signal can be separated as far as possible in the time domain, so that the sample dosage is increased to increase the separation degree of the main pulse and the reflected pulse in the sample signal in the time domain, however, because the measured substance has a certain dispersion for the terahertz wave beam, the shape of the reflected peak terahertz time domain pulse is widened, that is, compared with the real transmitted TDS signal, the shape of the reflected peak terahertz time domain pulse is deformed to a certain extent; in addition, for thinner samples, the tail of the reflected pulse signal and the tail of the true main pulse signal overlap, and fitting is difficult in a morphological mode, so that a plurality of prior parameters are required to be manually adjusted in the aforesaid methods, and a general method which does not need manual intervention on most samples cannot be formed.
Accordingly, it is desirable to solve the problem of how to provide a general method for achieving efficient filtering of absorption spectrum reflection peak interference fringes without manual intervention.
Disclosure of Invention
In view of the above-mentioned drawbacks of the prior art, the present invention is directed to providing a method, a system, a medium and a device for filtering reflection pulse interference when testing a THz-TDS sample, so as to solve the problem of how to provide a general method for filtering absorption spectrum reflection peak interference fringes with high efficiency without manual intervention in the prior art.
To achieve the above and other related objects, the present invention provides a method for filtering reflected pulse interference when testing a THz-TDS sample, comprising the steps of: testing to obtain a reference time domain signal T of THz-TDS without a sample Ref (T) testing the time domain signal of THz-TDS with sample as T Sam (t); for T Ref (t) performing FFT and calculating the frequency spectrum amplitude to obtain a corresponding frequency domain signal F without sample Ref (f) For T Sam (t) FFT and calculation of spectral amplitude, transformation to obtain the corresponding frequency domain signal F with sample Sam (f) Thereby obtaining terahertz frequency domain absorption spectrum signals A (F) =F of the sample Ref (f)-F Sam (f) The method comprises the steps of carrying out a first treatment on the surface of the Performing FFT conversion of spatial domain on the absorption spectrum signal A (f) to obtain corresponding separationThe fourier transform spectrum S (t), S (t) =fft [ a (f)]The method comprises the steps of carrying out a first treatment on the surface of the Thus, the original interference power spectrum density curve I (t) with different t as the abscissa is obtained, and I (t) = |S (t)/N| 2 N is the number of points for performing FFT conversion on the absorption spectrum A (f); filtering and iterating the original interference power spectrum density curve I (t) to obtain a new interference power spectrum density curve I new (t); combining the original interference power spectral density curve I (t) and the new interference power spectral density curve I new (t) comparing to obtain amplitude attenuation coefficient a of the corresponding filter band i ＝[I new (t i )/I(t i )] 1/2 (i=n-1, n, n+1); and according to the property S (t k )＝S(t N-k ) * (k=1 to N-1), and correcting the corresponding frequency point FFT conversion value in the discrete fourier transform spectrum S (t), thereby obtaining a filtered and corrected discrete fourier transform S new (t); discrete fourier transform after filtering correction S new (t) performing inverse discrete fourier transform to obtain an absorption spectrum after interference fringe filtering: a is that new (f)＝IFFT[S new (t)]。
In one embodiment of the present invention, the filtering iteration is performed on the original interference power spectral density curve I (t) to obtain a new interference power spectral density curve I new (t) comprises: taking the component t closest to the delay delta t of the main pulse and the first-stage reflected pulse of the sample signal in the original interference power spectral density curve I (t) n As the center frequency of the filter band, wherein N is the index number of the transverse axis t in I (t) (N E0-N-1); the free spectral range of the interference fringes is FSR: fsr=Δf=c/opd=1/Δt, where c is the speed of light, OPD is the optical path difference of two beams of light, opd=2n sam L is the thickness of the sample, n sam The terahertz wave band refractive index of the sample; taking t n Each of 1 frequency points on both sides is denoted as t n-1 ，t n ，t n+1 Forming a filter band; maximum I (t) corresponding to filter band frequency i ) The value (i=n-1, n, n+1) is noted as the maximum I (t i ) The value is I max Will I max Assigning an average value I to two adjacent frequency points I (t) new The method comprises the steps of carrying out a first treatment on the surface of the Repeating the maximum I (t) corresponding to the filter band frequency i ) The value (i=n-1, n, n+1), the most significantBig I (t) i ) The value is I max Will I max Assigning an average value I to two adjacent frequency points I (t) new The method comprises the steps of carrying out a first treatment on the surface of the Until any of the following cycle stop conditions is reached: reaching the appointed filtering times; or I max <I th ，I th Is a set threshold value; or when I new ≥I max When in use; thereby obtaining a filtered interference power spectral density curve I new (t), wherein t=t k ,(k∈0～N-1)。
In an embodiment of the invention, the method for filtering the reflected pulse interference during the THz-TDS test is applied to the transmission THz-TDS; placing a sample in the terahertz wave beam focusing position to obtain a time domain signal T of the sample after the terahertz wave beam penetrates through the sample Sam (t)。
In one embodiment of the present invention, the property S (t k )＝S(t N-k ) * (k=1 to N-1), and correcting the corresponding frequency point FFT conversion value in the original S (t), thereby obtaining a filtered and corrected discrete fourier transform S new (t) comprises:
S new (t i )＝S(t i )/a i (i＝n-1,n,n+1)
S new (t N-i )＝S(t N-i )/a i (i＝n-1,n,n+1)
S new (t j )＝S(t j )(j≠n-1,n,n+1,N-n-1,N-n,N-n+1)。
in order to achieve the above object, the present invention further provides a reflected pulse interference filtering system for THz-TDS test samples, comprising: the device comprises a testing module, a transformation module, a discrete transformation module, a filtering iteration module, a filtering correction module and an inverse transformation module; the test module is used for testing that the reference time domain signal of THz-TDS is T when no sample is obtained Ref (T) testing the time domain signal of THz-TDS with sample as T Sam (t); the transformation module is used for T Ref (t) performing FFT and calculating the frequency spectrum amplitude to obtain a corresponding frequency domain signal F without sample Ref (f) For T Sam (t) performing FFT and calculating the frequency spectrum amplitude to obtain corresponding frequency domain information when the sample existsNumber F Sam (f) Thereby obtaining terahertz frequency domain absorption spectrum signals A (F) =F of the sample Ref (f)-F Sam (f) The method comprises the steps of carrying out a first treatment on the surface of the The discrete transformation module is used for performing FFT transformation of a spatial domain on the absorption spectrum signal A (f) to obtain a corresponding discrete Fourier transformation spectrum S (t), S (t) =FFT [ A (f)]The method comprises the steps of carrying out a first treatment on the surface of the Thus, the original interference power spectrum density curve I (t) with different t as the abscissa is obtained, and I (t) = |S (t)/N| 2 N is the number of points for performing FFT conversion on the absorption spectrum A (f); the filtering iteration module is used for carrying out filtering iteration on the original interference power spectrum density curve I (t) to obtain a new interference power spectrum density curve I new (t); the filtering correction module is used for correcting the original interference power spectrum density curve I (t) and the new interference power spectrum density curve I new (t) comparing to obtain amplitude attenuation coefficient a of the corresponding filter band i ＝[I new (t i )/I(t i )] 1/2 (i=n-1, n, n+1); and according to the property S (t k )＝S(t N-k ) * (k=1 to N-1), and correcting the corresponding frequency point FFT conversion value in the discrete fourier transform spectrum S (t), thereby obtaining a filtered and corrected discrete fourier transform S new (t); the inverse transformation module is used for transforming the discrete Fourier transform S after the filtering correction new (t) performing inverse discrete fourier transform to obtain an absorption spectrum after interference fringe filtering: a is that new (f)＝IFFT[S new (t)]。
In an embodiment of the present invention, the filtering iteration module is configured to perform filtering iteration on the original interference power spectral density curve I (t) to obtain a new interference power spectral density curve I new (t) comprises: taking the component t closest to the delay delta t of the main pulse and the first-stage reflected pulse of the sample signal in the original interference power spectral density curve I (t) n As the center frequency of the filter band, wherein N is the index number of the transverse axis t in I (t) (N E0-N-1); the free spectral range of the interference fringes is FSR: fsr=Δf=c/opd=1/Δt, where c is the speed of light, OPD is the optical path difference of two beams of light, opd=2n sam L is the thickness of the sample, n sam The terahertz wave band refractive index of the sample; taking t n Each of 1 frequency points on both sides is denoted as t n-1 ，t n ，t n+1 Forming a filter band; maximum I (t) corresponding to filter band frequency i ) The value (i=n-1, n, n+1) is noted as the maximum I (t i ) The value is I max Will I max Assigning an average value I to two adjacent frequency points I (t) new The method comprises the steps of carrying out a first treatment on the surface of the Repeating the maximum I (t) corresponding to the filter band frequency i ) The value (i=n-1, n, n+1) is noted as the maximum I (t i ) The value is I max Will I max Assigning an average value I to two adjacent frequency points I (t) new The method comprises the steps of carrying out a first treatment on the surface of the Until any of the following cycle stop conditions is reached: reaching the appointed filtering times; or I max <I th ，I th Is a set threshold value; or when I new ≥I max When in use; thereby obtaining a filtered interference power spectral density curve I new (t), wherein t=t k ,(k∈0～N-1)。
In an embodiment of the invention, the method for filtering the reflected pulse interference during the THz-TDS test is applied to the transmission THz-TDS; placing a sample in the terahertz wave beam focusing position to obtain a time domain signal T of the sample after the terahertz wave beam penetrates through the sample Sam (t)。
In one embodiment of the present invention, the property S (t k )＝S(t N-k ) * (k=1 to N-1), and correcting the corresponding frequency point FFT conversion value in the original S (t), thereby obtaining a filtered and corrected discrete fourier transform S new (t) comprises:
S new (t i )＝S(t i )/a i (i＝n-1,n,n+1)
S new (t N-i )＝S(t N-i )/a i (i＝n-1,n,n+1)
S new (t j )＝S(t j )(j≠n-1,n,n+1,N-n-1,N-n,N-n+1)。
to achieve the above object, the present invention also provides a computer-readable storage medium having stored thereon a computer program which, when executed by a processor, implements any of the above-mentioned THz-TDS test sample reflection pulse interference filtering methods.
In order to achieve the above object, the present invention further provides a reflected pulse interference filtering device for THz-TDS test samples, comprising: a processor and a memory; the memory is used for storing a computer program; the processor is connected with the memory and is used for executing the computer program stored in the memory, so that the reflected pulse interference filtering device for the THz-TDS test sample executes any one of the reflected pulse interference filtering methods for the THz-TDS test sample.
Finally, the invention also provides a reflected pulse interference filtering system for THz-TDS test samples, comprising: the device comprises the THz-TDS test sample time reflection pulse interference filtering device and a communication signal transmitting device; the communication signal transmitting device is used for transmitting N times of transmitting signals with the number of M.
As described above, the method, the system, the medium and the device for filtering the reflected pulse interference during the THz-TDS test sample have the following beneficial effects: the prior acquisition of sample dispersion information or the time domain position of the reflected pulse signal is not needed, and the efficient filtering of the absorption spectrum reflection peak interference fringes is realized.
Drawings
FIG. 1a is a flow chart showing a method of reflection pulse interference filtering in a THz-TDS test sample according to an embodiment of the present invention;
FIG. 1b is a schematic diagram of a terahertz beam propagation model of the method for filtering out reflected pulse interference in a THz-TDS test sample according to an embodiment of the present invention;
FIG. 1c shows the method of the invention for reflected pulse interference filtering of THz-TDS test samples in an embodiment where the time domain signal of THz-TDS is T without sample Ref (T) time-domain signal T with THz-TDS in the presence of sample Sam (t) schematic;
FIG. 1d is a schematic diagram showing the absorption spectrum of the method for filtering the reflected pulse interference in the THz-TDS test sample according to one embodiment of the invention;
FIG. 1e is a diagram showing the original interference power spectral density curve I (t) of the method for filtering the reflected pulse interference in the THz-TDS test sample according to the invention;
FIG. 1f shows the time reversal of the THz-TDS test sample of the inventionMethod for filtering out interference of injection pulse in time domain signal of THz-TDS without sample in another embodiment is T Ref (T) time-domain signal T with THz-TDS in the presence of sample Sam (t) schematic;
FIG. 1g is a schematic diagram showing the absorption spectrum of a method for filtering out reflected pulse interference in a THz-TDS test sample according to another embodiment of the invention;
FIG. 1h is a diagram showing a new interference power spectral density curve of the method for filtering reflected pulse interference in the THz-TDS test sample according to the invention;
FIG. 1i is a schematic diagram showing an absorption spectrum of the method for filtering interference fringes by reflection pulse interference in the THz-TDS test sample according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a system for reflection pulse interference filtering in an embodiment of the THz-TDS test sample according to the present invention;
FIG. 3 is a schematic diagram of the device for filtering out the reflected pulse interference in one embodiment of the THz-TDS test sample according to the invention.
Description of element reference numerals
21. Test module
22. Conversion module
23. Discrete transformation module
24. Filtering iteration module
25. Filtering correction module
26. Inverse transformation module
31. Processor and method for controlling the same
32. Memory device
Detailed Description
Other advantages and effects of the present invention will become apparent to those skilled in the art from the following disclosure, which describes the embodiments of the present invention with reference to specific examples. The invention may be practiced or carried out in other embodiments that depart from the specific details, and the details of the present description may be modified or varied from the spirit and scope of the present invention. It should be noted that the following embodiments and features in the embodiments may be combined with each other without conflict.
It should be noted that the illustrations provided in the following embodiments merely illustrate the basic concept of the present invention by way of illustration, so that only the components related to the present invention are shown in the drawings and are not drawn according to the number, shape and size of the components in actual implementation, the form, number and proportion of each component in actual implementation may be arbitrarily changed, and the layout of the components may be more complicated.
According to the method, the system, the medium and the device for filtering the reflected pulse interference during the THz-TDS test of the sample, the prior acquisition of sample dispersion information or the time domain position of the reflected pulse signal is not needed, and the efficient filtering of the absorption spectrum reflection peak interference fringes is realized.
In one embodiment, as shown in FIG. 1a, the method for filtering the reflected pulse interference during the THz-TDS test of the invention comprises the following steps:
step S11, testing to obtain a reference time domain signal T of THz-TDS without a sample Ref (T) testing the time domain signal of THz-TDS with sample as T Sam (t)。
Specifically, the method for filtering out reflected pulse interference when the THz-TDS test sample is applied to the transmission THz-TDS; placing a sample in the terahertz wave beam focusing position to obtain a time domain signal T of the sample after the terahertz wave beam penetrates through the sample Sam (t). The time domain signal of THz-TDS without sample is T Ref And (t) is the reference time domain signal.
Specifically, for the sample signal received during transmission measurement of the THz-TDS system, a time domain and frequency domain joint analysis is performed to eliminate interference caused by reflection of upper and lower surfaces of the sample. The terahertz beam propagation model of the THz-TDS system in transmission type measurement of the sample is shown in fig. 1b, wherein 11 is an incident terahertz beam, 12 is a main pulse signal transmission path, 13 is a first-stage reflected pulse signal transmission path, and 14 is a transmission type measurement sample thickness L. The application mode of the system is that the time domain signal of THz-TDS is T when no sample is tested firstly Ref (t) then placing a sample at the terahertz beam focusing position, and testing the time domain signal of THz-TDS after passing through the sampleNumber T Sam (T) the time domain signal of THz-TDS without sample is T Ref (T) time-domain signal T with THz-TDS in the presence of sample Sam (T) As shown generally in FIG. 1c, T Sam In addition to the main pulse signal transmitted through the sample, there is a significant reflected pulse signal introduced by reflection from the upper and lower surfaces of the sample. Wherein 15 is the main pulse of the time domain signal of THz-TDS without sample (i.e. the main pulse of the time domain signal of reference THz-TDS), 16 is the main pulse of the time domain signal of THz-TDS with sample, 17 is the first-stage reflected pulse of the time domain signal of THz-TDS with sample, and 18 is the delay delta t of the main pulse of the time domain signal of THz-TDS with sample and the first-stage reflected pulse.
Step S12, pair T Ref (t) performing FFT and calculating the frequency spectrum amplitude to obtain a corresponding frequency domain signal F without sample Ref (f) For T Sam (t) FFT and calculation of spectral amplitude, transformation to obtain the corresponding frequency domain signal F with sample Sam (f) Thereby obtaining terahertz frequency domain absorption spectrum signals A (F) =F of the sample Ref (f)-F Sam (f)。
Specifically, the amplitude of the TDS time domain signal is proportional to the electric field intensity of the terahertz wave beam, the terahertz wave beam is reflected twice on the upper and lower surfaces of the sample according to the fresnel reflection law, no matter the polarization direction of the incident wave beam is s polarization or t polarization, the phase of the reflected pulse signal is the same as that of the main pulse signal, i.e., in the time domain signal, the polarity of the reflected pulse is identical to that of the main pulse (the same positive or same negative amplitude), so that the time domain delay Δt between the reflected pulse and the main pulse can be obtained from the time domain signal by searching for an extreme point; it should be noted that, because the sample to be measured has dispersion on the terahertz signal, and meanwhile, some samples have certain trailing on the main pulse of the terahertz signal, there is deformation such as pulse broadening in the time domain between the reflection peak signal and the main pulse, so Δt is not the exact position where the reflection pulse occurs, but only approximately reflects the approximate delay relationship between the main pulse and the reflection pulse signal. According to Fresnel reflection law, when the first-stage reflected pulse is subjected to interface reflection twice, the electric field intensity ratio of the reflected signal to the incident signal is (n) sam -n air ) 2 /(n sam +n air ) 2 Wherein n is air Is the refractive index of air (n air ＝1),n sam Is the terahertz wave band refractive index of the sample (typically n of the sample sam >1.3 The electric field amplitude of the multi-stage reflected pulse is therefore negligible relative to the electric field amplitude of the main pulse, i.e. only the effect of the first-stage reflected pulse has to be taken into account in the time-domain signal of the sample. For T Ref (t) performing FFT (fast Fourier transform) to obtain corresponding sample-free time-frequency domain signal F Ref (f) For T Sam (t) FFT transforming to obtain corresponding time-frequency domain signal F with sample Sam (f) From the time-frequency domain signal F with sample Sam (f) Deducting the time-frequency domain signal F without sample Ref (f) Thereby obtaining terahertz frequency domain absorption spectrum signals A (F) =F of the sample Ref (f)-F Sam (f) (the ordinate of the frequency domain signal of the terahertz frequency domain absorption spectrum signal a (f) is logarithmic). The method is a conventional THz-TDS sample terahertz wave band absorption spectrum acquisition method. If the reflected pulse signal is not filtered out, obvious interference fringes can appear in the absorption spectrum. When the contrast of the interference fringes is large, not only false absorption peaks are introduced, but also true absorption peak information can be submerged in severe cases, so that serious errors are generated in the absorption spectrum test, as shown in fig. 1 d. 19 is an interference fringe in the absorption spectrum, and 110 is an interference fringe FSR (which can be regarded as a period of the interference fringe).
Step S13, performing spatial-domain FFT transformation on the absorption spectrum signal a (f) to obtain a corresponding discrete fourier transform spectrum S (t), S (t) =fft [ a (f)]The method comprises the steps of carrying out a first treatment on the surface of the Thus, the original interference power spectrum density curve I (t) with different t as the abscissa is obtained, and I (t) = |S (t)/N| 2 N is the number of points at which the absorption spectrum a (f) is FFT-transformed.
Specifically, N is the number of points for performing FFT transformation on the absorption spectrum a (f), taking the number of data points of a (f), i.e., I (t) = |s (t)/n|s (t) 2 In t=t k (k.epsilon.0-N-1) is a set of discrete points. The physical meaning of I (t) is that for the absorption spectrum signal A (f), it can be decomposed into a superposition of a plurality of sinusoidal interference components, each interference component corresponding to a different main pulse signal and a first-order reflected pulse signalDelay t; in I (t), except for the direct current component and the linear drift (usually caused by scattering), the interference signal power corresponding to delta t is far stronger than the power of other interference components and is weaker, and the delta t component, the direct current component and the linear drift component are far separated from each other on the transverse axis, so that interference and erroneous judgment are not introduced. Wherein, the component t closest to Deltat in the original interference power spectrum density curve I (t) is taken n As the center frequency of the filter band, wherein N is the index number of the transverse axis t in I (t) (N E0-N-1); the free spectral range of the interference fringes is FSR: fsr=Δf=c/opd=1/Δt, where c is the speed of light, OPD is the optical path difference of two beams of light, opd=2n sam L is the thickness of the sample, n sam Is the terahertz wave band refractive index of the sample. Thus, the frequency domain interference period DeltaF of the absorption spectrum interference fringe and the time domain signal T of THz-TDS in the presence of a sample are established Sam The relationship between the main pulse and the first order reflected pulse delay Δt in (t). As can be seen from fsr=Δf=c/opd=1/Δt, when the amount of the sample is increased, the thickness L of the sample can be increased accordingly, so that the OPD of the main beam and the first-stage reflected beam and the separation degree Δt of the two in the time-domain signal are increased, which is the precondition of the conventional time-domain filtering.
S14, filtering and iterating the original interference power spectrum density curve I (t) to obtain a new interference power spectrum density curve I new (t)。
Due to various reasons such as sample dispersion, noise, scattering, uneven sample interface and the like, interference fringes in the obtained sample absorption spectrum are not ideal periodic signals taking 1/deltat as a period, namely, in I (t), an impulse function delta (deltat) taking deltat as an abscissa is usually not existed, but a power spectrum envelope taking deltat as a center is adopted, and interference component power corresponding to different t values in a corresponding interval is gradually reduced by filtering the power spectrum envelope. The fence effect and the influence caused by frequency domain signal leakage in the FFT conversion process can be removed by adopting the following method.
Specifically, as shown in FIG. 1e, the original interference power spectral density curve I (t), wherein 111 is the original interference power spectral density curveCorresponding maxima t in the line n Position. Filtering and iterating the original interference power spectrum density curve I (t) to obtain a new interference power spectrum density curve I new (t) comprises: taking the component t closest to the delay delta t of the main pulse and the first-stage reflected pulse of the sample signal in the original interference power spectral density curve I (t) n As the center frequency of the filter band, wherein N is the index number of the transverse axis t in I (t) (N E0-N-1); the free spectral range of the interference fringes is FSR: fsr=Δf=c/opd=1/Δt, where c is the speed of light, OPD is the optical path difference of two beams of light, opd=2n sam L is the thickness of the sample, n sam The terahertz wave band refractive index of the sample; the free spectral range of the interference fringes is the FSR (i.e., the frequency separation between two adjacent minima or maxima in the interference fringes). Taking t n Each of 1 frequency points on both sides is denoted as t n-1 ，t n ，t n+1 Forming a filter band; maximum I (t) corresponding to filter band frequency i ) The value (i=n-1, n, n+1) is noted as the maximum I (t i ) The value is I max Will I max Assigning an average value I to two adjacent frequency points I (t) new The method comprises the steps of carrying out a first treatment on the surface of the Note that if I max The corresponding frequency point is not t n But t n-1 Or t n+1 Then the sequence number of one adjacent frequency point is not in the filter band. Repeating the maximum I (t) corresponding to the filter band frequency i ) The value (i=n-1, n, n+1) is noted as the maximum I (t i ) The value is I max Will I max Assigning an average value I to two adjacent frequency points I (t) new The method comprises the steps of carrying out a first treatment on the surface of the Until any of the following cycle stop conditions is reached: reaching the appointed filtering times; or I max <I th ，I th Is a set threshold value; or when I new ≥I max When in use; thereby obtaining a filtered interference power spectral density curve I new (t), wherein t=t k (k.epsilon.0-N-1). Wherein S (t) k )＝S(t N-k ) * (k=1 to N-1) and I new (t)，t＝t k And k (k E0-N-1) belongs to the same k, but the value ranges are different.
S15, combining the original interference power spectral density curve I (t) and the new interference power spectral density curve I new (t) comparing to obtain amplitude attenuation coefficient a of the corresponding filter band i ＝[I new (t i )/I(t i )] 1/2 (i=n-1, n, n+1); and according to the property S (t k )＝S(t N-k ) * (k=1 to N-1), and correcting the corresponding frequency point FFT conversion value in the discrete fourier transform spectrum S (t), thereby obtaining a filtered and corrected discrete fourier transform S new (t)。
Specifically, the property S (t k )＝S(t N-k ) * (k=1 to N-1), and correcting the corresponding frequency point FFT conversion value in the original S (t), thereby obtaining a filtered and corrected discrete fourier transform S new (t) comprises: s is S new (t i )＝S(t i )/a i (i＝n-1,n,n+1)；S new (t N-i )＝S(t N-i )/a i (i＝n-1,n,n+1)；S new (t j )＝S(t j )(j≠n-1,n,n+1,N-n-1,N-n,N-n+1)。
Step S16, performing discrete Fourier transform S after filtering correction new (t) performing inverse discrete fourier transform to obtain an absorption spectrum after interference fringe filtering: a is that new (f)＝IFFT[S new (t)]。
Specifically, the filtered absorbance spectrum A is completed new (f) Compared with the original absorption spectrum A (f), the method can effectively reduce the interference fringes of the absorption spectrum introduced by the first-stage reflection pulse of the sample, and simultaneously can effectively maintain the form of the real absorption peak of the sample in the absorption spectrum. By the method, under the condition that the prior acquisition of the sample dispersion information is not needed, the accurate time domain position of the reflected pulse signal is not needed to be known, the efficient filtering of the absorption spectrum reflection peak interference fringes is realized, and the real absorption peak waveform is not seriously influenced. Meanwhile, the method does not need the precondition that the reflection pulse and the main pulse required by the conventional time domain reflection peak filtering method are completely separated in the time domain, so that the common time domain filtering method fails when the reflection pulse and the main pulse overlap for some thinner samples or samples with longer tail of the main pulse, and the method can still effectively filter the absorption spectrumThereby widening the application range of THz-TDS.
Specifically, as shown in fig. 1f, in an embodiment, 60mg of pyrazinamide pure product is ground and pressed into tablets to form a test sample piece with the diameter of 13mm and the thickness of L of 0.4mm, and a transmission type THz-TDS system is used for respectively testing and obtaining a time domain signal of THz-TDS without sample as T Ref (T) 112, testing the THz-TDS time domain signal with sample as T Sam (t) 113 As shown in FIG. 1f, the first order reflected signal and the main pulse have a delay Δt of 8.16ps, which is derived from the time domain signal of THz-TDS with sample (sample transmitted time domain signal 113). The time domain signal T of THz-TDS without sample Ref (T) 112 and THz-TDS with sample time Domain Signal T Sam (t) 113 performing FFT conversion to obtain respective frequency domain signals, and subtracting the frequency domain signals of the sample from the reference frequency domain signals to obtain absorption spectrum signals of the sample sheet of the pyrazinamide to be tested, as shown in fig. 1g, when no processing is performed on the reflection peak in the time domain signal of THz-TDS when the sample is present, there is a very obvious interference fringe in the absorption spectrum, and serious interference exists on the true absorption peak of the sample. The absorption spectrum shown in fig. 1g is subjected to interference power spectrum analysis, specifically, the absorption spectrum signal a (f) is subjected to spatial-domain FFT transformation, to obtain a corresponding discrete fourier transform spectrum S (t), S (t) =fft [ a (f) ]The method comprises the steps of carrying out a first treatment on the surface of the Thus, the original interference power spectrum density curve I (t) with different t as the abscissa is obtained, and I (t) = |S (t)/N| 2 N is the number of points for performing FFT transformation on the absorption spectrum A (f), and the corresponding I (t) is obtained. Then, find the filter band center point t corresponding to Δt from I (t) n Filtering and iterating the original interference power spectrum density curve I (t) to obtain a new interference power spectrum density curve I new (t) as shown in FIG. 1 h. In this example, the iteration termination condition used is when I new ≥I max And when the filtering iteration is stopped, in the example, the filtering is completed after 3 iterations, and the speed is high. For the new interference power spectrum density curve I after the filtering new (t) performing inverse discrete Fourier transform to obtain an absorption spectrum with interference fringes removed, as shown in FIG. 1 i. As can be seen by comparing FIGS. 1g and 1iThe interference fringes are greatly inhibited, and the real absorption peak of the pyrazinamide can still be maintained, for example, in the figure 1i, three obvious absorption peaks are respectively positioned at 0.50,0.72 and 1.47THz in the filtered pyrazinamide absorption spectrum, and the obtained product corresponds to literature (Zhang Qi, fang Hongxia, qin Dan, and the like), "the terahertz time-domain spectroscopy technology is used for qualitatively and quantitatively analyzing pyrazinamide and isoniazid in antitubercular drugs", "journal of drug analysis, volume 36, 6 th period, 1082-1088, 2016); in the example, the total amount of the used substances is only 60mg, the thickness is only 0.4mm, and compared with the 280mg and the test sample sheet with the thickness of 1.5mm used in the literature, the sample consumption and the thickness of the sample sheet can be greatly reduced, so that the test capability of the THz-TDS system on the sample with less substance content is improved.
As shown in fig. 2, in one embodiment, the system for filtering out reflected pulse interference during THz-TDS testing of a sample of the present invention includes a testing module 21, a transforming module 22, a discrete transforming module 23, a filtering iteration module 24, a filtering correction module 25 and an inverse transforming module 26; the test module is used for testing that the reference time domain signal of THz-TDS is T when no sample is obtained Ref (T) testing the time domain signal of THz-TDS with sample as T Sam (t); the transformation module is used for T Ref (t) performing FFT and calculating the frequency spectrum amplitude to obtain a corresponding frequency domain signal F without sample Ref (f) For T Sam (t) performing FFT conversion and calculating the frequency spectrum amplitude to obtain a corresponding frequency domain signal F with a sample Sam (f) Thereby obtaining terahertz frequency domain absorption spectrum signals A (F) =F of the sample Ref (f)-F Sam (f) The method comprises the steps of carrying out a first treatment on the surface of the The method comprises the steps of carrying out a first treatment on the surface of the The discrete transformation module is used for performing FFT transformation of a spatial domain on the absorption spectrum signal A (f) to obtain a corresponding discrete Fourier transformation spectrum S (t), S (t) =FFT [ A (f)]The method comprises the steps of carrying out a first treatment on the surface of the Thus, the original interference power spectrum density curve I (t) with different t as the abscissa is obtained, and I (t) = |S (t)/N| 2 N is the number of points for performing FFT conversion on the absorption spectrum A (f); the filtering iteration module is used for carrying out filtering iteration on the original interference power spectrum density curve I (t) to obtain a new interference power spectrum density curve I new (t); the filtering correction module is used for correcting the original interference power spectrum density curve I #t) and a new interference power spectral density curve I new (t) comparing to obtain amplitude attenuation coefficient a of the corresponding filter band i ＝[I new (t i )/I(t i )] 1/2 (i=n-1, n, n+1); and according to the property S (t k )＝S(t N-k ) * (k=1 to N-1), and correcting the corresponding frequency point FFT conversion value in the discrete fourier transform spectrum S (t), thereby obtaining a filtered and corrected discrete fourier transform S new (t); the inverse transformation module is used for transforming the discrete Fourier transform S after the filtering correction new (t) performing inverse discrete fourier transform to obtain an absorption spectrum after interference fringe filtering: a is that new (f)＝IFFT[S new (t)]。
The filtering iteration module is used for carrying out filtering iteration on the original interference power spectrum density curve I (t) to obtain a new interference power spectrum density curve I new (t) comprises: component t of the delay delta t of the main pulse and the first-stage reflected pulse of the sample signal n As the center frequency of the filter band, wherein N is the index number of the transverse axis t in I (t) (N E0-N-1); the free spectral range of the interference fringes is FSR: fsr=Δf=c/opd=1/Δt, where c is the speed of light, OPD is the optical path difference of two beams of light, opd=2n sam L is the thickness of the sample, n sam The terahertz wave band refractive index of the sample; taking t n Each of 1 frequency points on both sides is denoted as t n-1 ，t n ，t n+1 Forming a filter band; maximum I (t) corresponding to filter band frequency i ) The value (i=n-1, n, n+1) is noted as the maximum I (t i ) The value is I max Will I max Assigning an average value I to two adjacent frequency points I (t) new The method comprises the steps of carrying out a first treatment on the surface of the Repeating the maximum I (t) corresponding to the filter band frequency i ) The value (i=n-1, n, n+1) is noted as the maximum I (t i ) The value is I max Will I max Assigning an average value I to two adjacent frequency points I (t) new The method comprises the steps of carrying out a first treatment on the surface of the Until any of the following cycle stop conditions is reached: reaching the appointed filtering times; or I max <I th ，I th Is a set threshold value; or when I new ≥I max When in use; thereby obtaining a filtered interference power spectral density curve I new (t), wherein t=t k ,(k∈0～N-1)。
In an embodiment of the invention, the method for filtering the reflected pulse interference during the THz-TDS test is applied to the transmission THz-TDS; placing a sample in the terahertz wave beam focusing position to obtain a time domain signal T of the sample after the terahertz wave beam penetrates through the sample Sam (t)。
In one embodiment of the present invention, the property S (t k )＝S(t N-k ) * (k=1 to N-1), and correcting the corresponding frequency point FFT conversion value in the original S (t), thereby obtaining a filtered and corrected discrete fourier transform S new (t) comprises:
S new (t i )＝S(t i )/a i (i＝n-1,n,n+1)
S new (t N-i )＝S(t N-i )/a i (i＝n-1,n,n+1)
S new (t j )＝S(t j )(j≠n-1,n,n+1,N-n-1,N-n,N-n+1)。
it should be noted that, the structures and principles of the test module 21, the transform module 22, the discrete transform module 23, the filter iteration module 24, the filter correction module 25 and the inverse transform module 26 are in one-to-one correspondence with the steps in the reflection pulse interference filtering method when the THz-TDS test sample is performed, so that the description thereof is omitted here.
It should be noted that, it should be understood that the division of the modules of the above system is merely a division of a logic function, and may be fully or partially integrated into a physical entity or may be physically separated. And these modules may all be implemented in software in the form of calls by the processing element; or can be realized in hardware; the method can also be realized in a form of calling software by a processing element, and the method can be realized in a form of hardware by a part of modules. For example, the x module may be a processing element that is set up separately, may be implemented in a chip of the apparatus, or may be stored in a memory of the apparatus in the form of program code, and the function of the x module may be called and executed by a processing element of the apparatus. The implementation of the other modules is similar. In addition, all or part of the modules can be integrated together or can be independently implemented. The processing element described herein may be an integrated circuit having signal processing capabilities. In implementation, each step of the above method or each module above may be implemented by an integrated logic circuit of hardware in a processor element or an instruction in a software form.
For example, the modules above may be one or more integrated circuits configured to implement the methods above, such as: one or more application specific integrated circuits (Application Specific Integrated Circuit, abbreviated as ASIC), or one or more microprocessors (Micro Processor Uint, abbreviated as MPU), or one or more field programmable gate arrays (Field Programmable Gate Array, abbreviated as FPGA), or the like. For another example, when a module above is implemented in the form of a processing element scheduler code, the processing element may be a general-purpose processor, such as a central processing unit (Central Processing Unit, CPU) or other processor that may invoke the program code. For another example, the modules may be integrated together and implemented in the form of a system-on-a-chip (SOC).
In an embodiment of the present invention, the present invention further includes a computer readable storage medium having a computer program stored thereon, which when executed by a processor implements any of the above methods for reflected pulse interference filtering of THz-TDS test samples.
Those of ordinary skill in the art will appreciate that: all or part of the steps for implementing the method embodiments described above may be performed by computer program related hardware. The aforementioned computer program may be stored in a computer readable storage medium. The program, when executed, performs steps including the method embodiments described above; and the aforementioned storage medium includes: various media that can store program code, such as ROM, RAM, magnetic or optical disks.
In one embodiment, as shown in FIG. 3, the reflected pulse interference filtering device for THz-TDS test sample of the present invention comprises: a processor 31 and a memory 32; the memory 32 is used for storing a computer program; the processor 31 is connected to the memory 32, and is configured to execute a computer program stored in the memory 32, so that the reflection pulse interference filtering device executes any one of the reflection pulse interference filtering methods when the THz-TDS test sample is tested.
Specifically, the memory 32 includes: various media capable of storing program codes, such as ROM, RAM, magnetic disk, U-disk, memory card, or optical disk.
Preferably, the processor 31 may be a general-purpose processor, including a central processing unit (Central Processing Unit, abbreviated as CPU), a network processor (Network Processor, abbreviated as NP), etc.; but also digital signal processors (Digital Signal Processor, DSP for short), application specific integrated circuits (Application Specific Integrated Circuit, ASIC for short), field programmable gate arrays (Field Programmable Gate Array, FPGA for short) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components.
In summary, the method, the system, the medium and the device for filtering the reflected pulse interference during the THz-TDS test of the sample do not need to acquire the dispersion information of the sample or the time domain position of the reflected pulse signal in advance, and the efficient filtering of the interference fringes of the reflection peak of the absorption spectrum is realized. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.
The above embodiments are merely illustrative of the principles of the present invention and its effectiveness, and are not intended to limit the invention. Modifications and variations may be made to the above-described embodiments by those skilled in the art without departing from the spirit and scope of the invention. Accordingly, it is intended that all equivalent modifications and variations of the invention be covered by the claims, which are within the ordinary skill of the art, be within the spirit and scope of the present disclosure.
Claims (8)
1. The method for filtering the reflected pulse interference during THz-TDS test of the sample is characterized by comprising the following steps:
testing to obtain a reference time domain signal T of THz-TDS without a sample Ref (t) testObtaining the time domain signal of THz-TDS as T when the sample exists Sam (t)；
For T Ref (t) performing FFT and calculating the frequency spectrum amplitude to obtain a corresponding frequency domain signal F without sample Ref (f) For T Sam (t) FFT and calculation of spectral amplitude, transformation to obtain the corresponding frequency domain signal F with sample Sam (f) Thereby obtaining terahertz frequency domain absorption spectrum signals A (F) =F of the sample Ref (f)-F Sam (f)；
Performing FFT conversion of a spatial domain on the absorption spectrum signal A (f) to obtain a corresponding discrete Fourier transform spectrum S (t) i )，S(t i )＝FFT[A(f)]The method comprises the steps of carrying out a first treatment on the surface of the Thereby obtaining the reflected pulse to-be-filtered signal I (t) i )，I(t i )＝|S(t i )/N| 2 (i=0, 1, …, N-1), N being the number of points at which the absorption spectrum a (f) is FFT-transformed;
for the reflected pulse to be filtered signal I (t i ) Filtering and iterating to obtain a reflected pulse filtered signal I new (t i ) The method comprises the steps of carrying out a first treatment on the surface of the -filtering said reflected pulse signal I (t i ) And reflected pulse filtered signal I new (t i ) Comparing to obtain amplitude attenuation coefficient a of corresponding filter band i ＝[I new (t i )/I(t i )] 1/2 (i=0, 1, …, N-1); correcting the discrete fourier transform spectrum S (t i ) Corresponding frequency point FFT conversion value in the filter correction, thereby obtaining the filtered and corrected discrete Fourier transform S new (t i )；
Discrete fourier transform after filtering correction S new (t i ) And then performing inverse discrete Fourier transform to obtain an absorption spectrum after interference fringe filtering: a is that new (f)＝IFFT[S new (t i )]；
The pair of reflected pulses is to be filtered signal I (t i ) Filtering and iterating to obtain a reflected pulse filtered signal I new (t i ) Comprising the following steps:
taking the reflected pulse to-be-filtered signal I (t) i ) The component t closest to the delay delta t of the main pulse and the first-stage reflected pulse of the sample signal n As the center frequency of the filter band, where n is I (t i ) Subscript number of middle horizontal axis t, (n=1, …, N-2); the free spectral range of the interference fringes is FSR: fsr=Δf=c/opd=1/Δt, where c is the speed of light, OPD is the optical path difference of two beams of light, opd=2n sam L is the thickness of the sample, n sam The terahertz wave band refractive index of the sample;
taking t n Each of 1 frequency points on both sides is denoted as t n-1 ，t n ，t n+1 Forming a filter band;
find the maximum I (t) corresponding to the filter band frequency j ) The value (j=n-1, n, n+1) is noted as the maximum I (t j ) The value is I max Will I max Assigned as two adjacent frequency points I (t j ) Average value of the values I new ；
Repeating the above steps until any one of the following cycle stop conditions is reached: reaching the appointed filtering times; or I max <I th ，I th Is a set threshold value; or when I new ≥I max When in use; thereby obtaining a reflected pulse filtered signal I new (t i )。
2. The method for filtering out reflected pulse interference when testing a sample according to claim 1, wherein the method for filtering out reflected pulse interference when testing a sample is THz-TDS is applied to transmission type THz-TDS; placing a sample in the terahertz wave beam focusing position to obtain a time domain signal T of the sample after the terahertz wave beam penetrates through the sample Sam (t)。
3. The method of claim 1, wherein the correction of the original S (t i ) Corresponding frequency point FFT conversion value in the filter correction, thereby obtaining the filtered and corrected discrete Fourier transform S new (t i ) Including using formula S new (t i )＝S(t i )/a i (i＝0,1,…,N-1)。
4. A reflected pulse interference filtering system for THz-TDS testing of a sample, comprising: the device comprises a testing module, a transformation module, a discrete transformation module, a filtering iteration module, a filtering correction module and an inverse transformation module;
the test module is used for testing that the reference time domain signal of THz-TDS is T when no sample is obtained Ref (T) testing the time domain signal of THz-TDS with sample as T Sam (t)；
The transformation module is used for T Ref (t) performing FFT and calculating the frequency spectrum amplitude to obtain a corresponding frequency domain signal F without sample Ref (f) For T Sam (t) performing FFT conversion and calculating the frequency spectrum amplitude to obtain a corresponding frequency domain signal F with a sample Sam (f) Thereby obtaining terahertz frequency domain absorption spectrum signals A (F) =F of the sample Ref (f)-F Sam (f)；
The discrete transformation module is used for performing FFT transformation of a spatial domain on the absorption spectrum signal A (f) to obtain a corresponding discrete Fourier transformation spectrum S (t) i )，S(t i )＝FFT[A(f)]The method comprises the steps of carrying out a first treatment on the surface of the Thereby obtaining the reflected pulse to-be-filtered signal I (t) i )，I(t i )＝|S(t i )/N| 2 (i=0, 1, …, N-1), N being the number of points at which the absorption spectrum a (f) is FFT-transformed;
the filtering iteration module is used for filtering the reflected pulse signal I (t i ) Filtering and iterating to obtain a reflected pulse filtered signal I new (t i )；
The filtering correction module is used for filtering the reflected pulse signal I (t i ) And reflected pulse filtered signal I new (t i ) Comparing to obtain amplitude attenuation coefficient a of corresponding filter band i ＝[I new (t i )/I(t i )] 1/2 (i=0, 1, …, N-1); correcting the discrete fourier transform spectrum S (t i ) Corresponding frequency point FFT conversion value in the filter correction, thereby obtaining the filtered and corrected discrete Fourier transform S new (t i )；
The inverse transformation module is used for transforming the discrete Fourier transform S after the filtering correction new (t i ) Re-enterInverse discrete fourier transform is performed to obtain an absorption spectrum after interference fringe filtering: a is that new (f)＝IFFT[S new (t i )]；
The filtering iteration module is used for filtering the reflected pulse signal I (t i ) Filtering and iterating to obtain a reflected pulse filtered signal I new (t i ) Comprising the following steps:
taking the reflected pulse to-be-filtered signal I (t) i ) The component t closest to the delay delta t of the main pulse and the first-stage reflected pulse of the sample signal n As the center frequency of the filter band, where n is I (t i ) Subscript number of middle horizontal axis t, (n=1, …, N-2); the free spectral range of the interference fringes is FSR: fsr=Δf=c/opd=1/Δt, where c is the speed of light, OPD is the optical path difference of two beams of light, opd=2n sam L is the thickness of the sample, n sam The terahertz wave band refractive index of the sample;
taking t n Each of 1 frequency points on both sides is denoted as t n-1 ，t n ，t n+1 Forming a filter band;
maximum I (t) corresponding to filter band frequency j ) The value (j=n-1, n, n+1) is noted as the maximum I (t j ) The value is I max Will I max Assigned as two frequency points I (t j ) Average value of the values I new ；
Repeating the above steps until any one of the following cycle stop conditions is reached: reaching the appointed filtering times; or I max <I th ，I th Is a set threshold value; or when I new ≥I max When in use; thereby obtaining a reflected pulse filtered signal I new (t i )。
5. The THz-TDS test sample time reflection pulse interference filtering system of claim 4, wherein the THz-TDS test sample time reflection pulse interference filtering method is applied to transmission THz-TDS; placing a sample in the terahertz wave beam focusing position to obtain a time domain signal T of the sample after the terahertz wave beam penetrates through the sample Sam (t)。
6. The THz-TDS test sample time reflection pulse interference filtering system according to claim 4, wherein the correction of the original S (t i ) Corresponding frequency point FFT conversion value in the filter correction, thereby obtaining the filtered and corrected discrete Fourier transform S new (t i ) Including using formula S new (t i )＝S(t i )/a i (i＝0,1,…,N-1)。
7. A computer readable storage medium having stored thereon a computer program, wherein the computer program is executed by a processor to implement the method of reflected pulse interference filtering when testing a sample according to any of claims 1 to 3.
8. A reflected pulse interference filtering device for THz-TDS test samples, comprising: a processor and a memory;
the memory is used for storing a computer program;
the processor is connected to the memory for executing the computer program stored in the memory, so that the reflected pulse interference filtering device when the THz-TDS test sample executes the reflected pulse interference filtering method when the THz-TDS test sample is any one of claims 1 to 3.
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Non-Patent Citations (1)
| Title |
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| THz-TDS测试中时域脉冲的本质段及其截取模型;苏海霞等;《光谱学与光谱分析》;20130415(第04期);全文 * |
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