Terahertz spectral analysis of Yunpian Lurong

Li-Na Zhang ,Yu-Hui Ma,Ze-Jia Zhang ,Kai-Xuan Hou ,Yan-Ming Wu,Guo-Wei Zhang *

1 College of Traditional Chinese Medicine, Hebei University, Baoding, China. 2 School of Electronics and Information Engineering,Hebei University,Baoding,China

Background

Lurong (cornu cervi pantotrichum), the stag of the Cervus Nippon Temminck or Cervus elaphus Linnaeus without ossification of the young horns [1]. Sexually sweet, warm and salty, with stronging kidney yang,nourishing qi and blood, stronging bones, and strengthening and nourishing marrow and essence. The Yunpian Lurong is one of the"four specialtise"in Qizhou.The so-called " Yunpian Lurong " is a thin sheet of Lurong that is cut into a shape like a cloud, thin as a scorpion,placed on the tip of the tongue,instantly melted[2].At present,many scholars use the traditional Chinese medicine fingerprint technology for the identification of Lurong medicinal materials [3]. This method of quality detection of medicinal materials requires pretreatment of the samples, which is complicated, time consuming and costly. Therefore, it is necessary to establish a non-destructive and rapid detection and analysis method to identify the Yunpian Lurong.

In order to establish a rapid detection method for Yunpian Lurong, this paper studied the similarities and differences between terahertz time domain spectrum,frequency domain spectrum, refractive index and absorption spectrum of Yunpian Lurong and conventional Lurong,which provides a basis for terahertz identification of Yunpian Lurong.

Materials and Methods

Experimental samples and preparation

In the experimental samples, the conventional Lurong is selected from the Oriental Medicine City of Anguo,Hebei, and the Yunpian Lurong is from Hebei Hancaotang Pharmaceutical Co. LTD, Anguo, Hebei(Figure 1). The samples were verified by the Liang Xianmao, a senior experimenter from the College of Traditional Chinese Medicine, Hebei University. The processing technology to produce Yunpian Lurong standard method.Take the Lurong,lick the hair,use a tool to scrape the net, wrap the body with a cloth bag,continuously pour the hot white wine into the small hole from the saw to the filling, infiltrate to the thoroughly,slightly steamed, cross-cut, flattened and dried [4]. Such processing can shorten the working procedure, the Lurong is easy to be steamed soft, with good thick piao clamping and cutting together when it is hot,the finished product surface is smooth, the piece shape is uniform, no peeling off the edge, no cracks, and the two surfaces are parallel. Cut into pieces, shaped like a cloud, thin as a scorpion,placed on the tip of the tongue,can be poured to melt[5].The two samples were dried in a forced air oven at 60 °C for 12 h. The sample name and thickness are shown in Table 1.

Figure 1 Two samples of Lurong

Table 1 sample name and thickness

Experimental device

This experiment uses a terahertz time-domain spectrometer (Daheng Xinjiyuan Technology Co. LTD.,DH-OTB-1000mm*600mm*500mm), and the system uses a femtosecond laser (American Spectroscopic Physics Corporation, Mai Tai). The laser is a pumping and detection source with a center source wavelength of 1550 nm,an output pulse width of approximately 92.3 fs,a pulse repetition rate of 80 MHz,and a Gaussian TEM00 beam of<1.2 mm.Its emitter is InAs crystals and detecter is ZnTe crystals.The spectral width of the source range is 0.2-2.8 THz. The experiment was carried out at room temperature. During the test, in order to avoid the influence of moisture in the air on the experiment, the system was filled with nitrogen gas during the measurement process to maintain a relative humidity<7%.

Experimental methods and data processing

The THz time domain signal of the sample was measured using a THz time domain spectrometer at room temperature using air as a reference. During the experiment, the ambient temperature of the instrument is about(25±1)°C,and the relative humidity is controlled at 7% or less [6]. Under this condition, the terahertz time-domain wave of air is accurately measured, and the measured results were used as a reference for the experiment. Subsequently, the terahertz time-domain spectrum of the conventional Lurong and Yunpian Lurong were measured, and each sample was measured 3 times,and each time was collcted using multiple parallel measurement methods. All the data in the experiment were collected by the terahertz spectroscopy system, and then relevant data were processed.

The time domain spectrum of the sample can be obtained first during the experiment, and the optical parameters of the sample are determined by the method proposed by Timothy et al. [7]. The reference signal and the sample signal distribution obtained by the Fourier transform are obtained to obtain the corresponding frequency domain spectrum [8], and the spectrum Er(ω) and Es(ω) can be obtained. The amplitude ratio wasand the phase difference was)(. The absorption coefficient and the refractive index were extracted by the Duvillaret method[9],and the absorption coefficient spectrum and a refractive index spectrum are obtained. And the formula for calculating the refractive index is:

The calculation formula of absorption coefficient is:

The approximate calculation formula for the absorption coefficient is:

In the calculation process of the above formula, c is the speed of light in vacuum, ω is the angular frequency,n(ω) represents the real part of the refractive index,which is closely related to the dispersion characteristics of the sample, while k（ω） represents the extinction coefficient,in which n(ω)=2ωk（ω）/c.This coefficient is also closely related to the absorption characteristics of the sample.A（ω） represents the ratio of the amplitude between the sample and the reference signal,(ω)represents the phase difference of the terahertz wave signal,and d represents the thickness of the tested sample,which can be obtained during the experiment.The unit of phase is the amplitude. Due to the effect of noise at low frequencies, the phase will undergo a 2 πjump [10]. In order to make the phase at the zero frequency closer to zero, the calibration method can be used as follows: the phase spectrum between the 0.5-1.2 THz linear range can be obtained by linear fitting method the phase valueat the zero frequency,such asπ can be integer N,and then the phase of all frequencies will be subtracted by 2πN[11].

Results

Terahertz time-domain spectrogram and analysis

According to the experimental data, the terahertz time-domain spectra of two kinds of Lurong samples and the reference signal were made respectively(Figure 2).In order to facilitate the observation, the time-domain spectra of the two kinds of samples and the reference signal were processed uniformly. The time-domain spectra of two kinds of Lurong samples and the reference signal at 0-1.5ps are shown in the figure. It can be seen from the time-domain spectrum that due to the differences in the thickness, refractive index and absorption coefficient of the samples, the THz spectrum of the sample has a certain degree of absorption and time delay of the terahertz pulse compared with the reference wave.Because of the scattering,reflection and absorption of the sample, the terahertz spectral amplitude is attenuated to a certain extent compared with the reference wave.

Terahertz frequency domain spectrum and analysis

The time-domain spectra of the two samples and the reference signal are processed by fast Fourier transform(FFT) to obtain the spectrum diagram of the sample signal and the reference signal (Figure 3). It can be seen from the figure that the terahertz frequency spectrum of Yunpian Lurong is obviously different from that of conventional Lurong, and the spectral intensity of pilose antler is larger than that of conventional velvet antler.There is a depression near 211 THz due to the absorption of water vapor. Due to the gradual enhancement of THz absorption and the gradual weakening of sample signal,the signal-to-noise ratio after 298 THz was too low. The effective spectrum range of the two Lurong samples in this paper was 0-298 THz. Compared with the spectrum of free space, the two kinds of Lurong samples have obvious absorption of THz wave, while the intensity and position of the absorption of yunpian Lurong and conventional Lurong were different, which provides a basis for the identification of yunpian Lurong.

Figure 2 The time-domain spectra of different samples

Figure 3 The frequency-domain spectra of samples

Refractive index curve and analysis

According to the above refraction index formula, the refraction index of two kinds of Lurong samples was obtained. Make the refractive index curve of the sample(Figure 4). By comparing and analyzing the refractive index curves of yunpian Lurong and conventional Lurong,it can be seen that the refractive index of yunpian Lurong and conventional Lurong was significantly different in the range of 0-8 THz. At 2.81, 5.82 and 7.63 THz, the refractive index of the two kinds of Lurong has obvious fluctuation. The average refractive index of the Yupian Lurong and conventional Lurong were about 1.11 and 0.56, respectively. Because the internal structure and composition of Yunpian Lurong are different from that of conventional Lurong,the difference of its refractive index may be related to the different internal structure and composition of Lurong.

Absorption coefficient curve and analysis

The absorption coefficients of two kinds of Lurong samples were obtained by calculating the experimental data in accordance with the above formula. The absorption coefficient curve of the sample was made(Figure 5). We can find that the absorption curve of yunpian Lurong and conventional Lurong is fluctuating greatly. The absorption coefficient of yunpian Lurong is less than that of conventional Lurong.And the absorption coefficient is obviously different, which may be caused by the difference of main chemical products contained in yunpian Lurong and conventional Lurong. When the frequency is between 0 and 2.4 THz, the terahertz absorption wave of Yupian Lurong and conventional velvet antler has no obvious characteristic absorption peak, but the absorption coefficient has obvious difference, which is convenient to distinguish the Yupian Lurong and can be used as an intuitive identification.When the frequency is between 2.4-3.5 Thz, with the increase of the terahertz incident wave frequency, the wave trends of two samples were similar and interlace with each other. To some extent, this trend further indicates that the basic substances of Yunpian Lurong are very similar to those of conventional Lurong, which is related to the fact that both of them are medicinal materials of Lurong.

Figure.4 The index of refraction of different samples

Figure 5 The absorption coefficient of different samples

Conclusion

Terahertz (1 THz=1O12 Hz) waves are electromagnetic waves with a frequency of 0.110 THz and a wavelength of 3 mm ~ 30 μ m, also known as T-rays. Its band is between infrared and microwave, which is the transition region from macroscopic electronics to microscopic photonics, and also the transition region from macroscopic classical theory to microscopic quantum theory [12], occupying a special position in the electromagnetic spectrum. Terahertz radiation can penetrate various materials[13],and is an effective means to identify the authenticity of traditional Chinese medicine,evaluate the quality of medicinal materials,and analyze the composition of medicinal materials [14]. It can detect the chemical and physical information contained in the materials [15]. Terahertz spectroscopy can be used to effectively identify different Lurongs.

As one of the " four specialties”in qizhou [16], the Yunpian Lurong has great significance in developing the detection method of its commodity specifications. In this study, under the condition of constant room temperature and drying, THz time-domain spectroscopy was used to detect and analyze the Lurong, providing a rapid and simple method for the identification of Lurong.The study found that the terahertz pulse can be absorbed and delayed to some extent due to the different thickness and refractive index between Yunpian Lurong and conventional Lurong. Because of scattering, reflection and absorption of the samples, the spectral amplitudes of the two samples decreased obviously compared with the reference waves.The terahertz spectra of the two kinds of Lurong are obviously different. Compared with the frequency spectrum of free space, both of them have obvious absorption of THz wave,but there are differences in the absorption intensity and location between Yunpian Lurong and conventional Lurong, which provides a basis for the identification of Yunpian Lurong. The refraction index of Yunpian Lurong is obviously different from that of conventional Lurong. The average refractive index of the Yunpian Lurong is greater than that of the conventional Lurong. This difference in refractive index may be related to the difference in the internal structure and composition of Yunpian Lurong and conventional Lurong. Therefore, the refractive index has guiding significance for the identification of Yunpian Lurong.The absorption coefficient of Yunpian Lurong was smaller than that of conventional Lurong, and there was a significant difference between the two samples, which may be related to the difference of main chemical products contained in the two samples. When the frequency is within the range of 0-2.4 Thz, there was a significant difference in the absorption coefficient between Yunpian Lurong and conventional Lurong,which is convenient to distinguish Yunpian Lurong and can be used as an intuitive identification. When the frequency is between 2.4-3.5 Thz,the fluctuation trend of the absorption wave of the two samples was similar and interlace with each other. To some extent, this further indicates that the basic substance of Yunpian Lurong is very similar to that of conventional Lurong. This is related to the fact that both of them are the medicinal materials of Lurong. We can detect this change by terahertz spectroscopy.

The experimental results show that the terahertz spectroscopy technology can quickly identify the Yunpian Lurong without destroying its surface and internal structure, and it can be used as a new detection technology. It has the characteristics of simple operation,short time-consuming, low cost, pollution-free. It can play a positive role for rapid detection of Yunpian Lurong.And it is a kind of promising Chinese herbal medicine quality analysis and identification of non-destructive sting methods. With the continuous combination of terahertz spectroscopy technology and the research field of traditional Chinese medicine, terahertz spectroscopy technology can be applied to the commercial specifications of Chinese medicinal materials,identification of authentic and fake products, and rapid detection of Chinese herbal medicine decoction pieces,providing a new method reference for the detection of traditional Chinese medicine [17], which will have a positive significance for the development of Chinese herbal medicine modernization.

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