Sample with no characteristic absorption can be identified by refractive index features. In this work, qualitative and quantitative identification of THz spectra of polypeptides using self-organization feature map (SOM) artificial neural network has been demonstrated. The absorption and refractive index features of three polypeptides, including Argreline Acetate, Alarelin Acetate, and Bivalirudin Trifluoroacetate, were measured by using the terahertz time-domain spectroscopy technique in the range 0.2–2.2 THz. The experimental results show that the three measured polypeptides present high similarity in absorption spectra but difference in refractive index spectra. After the network training process, the collected spectra were identified by the well-trained SOM network at another time. Analyzing the result we can see that the refractive index spectra are clustered and identify much better than the THz spectra of polypeptides. The study indicates that refractive index spectra can also be clustered by the SOM artificial neural network for identification of THz spectra especially when there is no obvious difference in absorption but significant difference in refractive index spectra.
We design a coupler for coupling parallel terahertz radiation into a terahertz anti-resonate waveguide sensor. It is the combination of a conical column and a short cylinder and made of aluminum. We simulate the coupler working in the case of a parallel terahertz wave and investigate the coupling results of both a broadband terahertz wave and a single frequency terahertz wave from free-space into an anti-resonate waveguide sensor. The results indicate that the transmission spectrum can be described as a sum of the transmission associated with the conical column and the cylinder part. We optimize the best dimension parameter of the coupler, with which we get the coupling ratio of 86.3% and the terahertz intensity concentration factor of 6.9.
We present an experimental study on a flexible terahertz (THz) pipe PMMA waveguide. The attenuation loss of this pipe
at 3.1THz was 9.65dB/m. Further more, bending loss of the pipe waveguides was investigated. The experimental result
shows good transmission properties of the pipe.
We present the simulation of an asymmetric double split-ring metamaterials absorber in terahertz region. The device consists of a metal/dielectric-spacer/metal structure allowing us select absorption by varying the asymmetric characteristics. When the two gaps are gradually away from the center in opposite direction, a giant amplitude modulation is observed at the fundamental inductive-capacitive (LC) resonance and the resonant frequencies are observed to red shifting. Besides, increasing the thickness of dielectric-spacer, the peak absorption can be changed. This theoretical simulation will be good reference for the follow experiments, and these asymmetric metamaterials absorbers is expected to be used as cloaking materials.
We report on transmission enhancement and suppression in rectangular aperture arrays at terahertz range. Experiments
and simulations reveal that transmission maxima and minima of metal film perforated with rectangular apertures arrays
are caused by the shape resonance and the interference between surface waves respectively. To further investigate the
relative contributions of shape resonance and interference between SPPs, we have examined the density of electrons
whose distribution property is identified to the normal component of E-filed which clearly shows that transmission
resonance stems from excitation of shape resonance at the edge of the hole. This resonance dominated by cutoff function
is responsible for resonance peak at transmitted spectrum. The interference of SPPs originated at surface further
enhances the resonances and gives a set of minima in the transmittance spectrum. This study contributes a better
understanding of fundamental physics behind the extraordinary transmission of aperture arrays at THz range and
provides a simple method for the design of THz devices.
The method of spectral dynamics analysis (SDA-method) is used for obtaining the2D THz signature of drugs. This
signature is used for the detection and identification of drugs with similar Fourier spectra by transmitted THz signal. We
discuss the efficiency of SDA method for the identification problem of pure methamphetamine (MA),
methylenedioxyamphetamine (MDA), 3, 4-methylenedioxymethamphetamine (MDMA) and Ketamine.
Terahertz time-domain spectroscopy (THz-TDS) is a new coherent spectral technique. In this
paper the spectral characteristics of air pollution gas, sulfur dioxide and hydrogen sulfide, had
been measured with THz-TDS in the range of 0.2-2.6THz. The result shows that both the gases
have equi-spaced absorption peaks and different gases have different intervals. We also
investigated the influence of pressure on absorption spectrum by changing the pressure of the
gases in a chamber. The experimental results indicate that the absorption peaks become
sharper with increasing the pressure. Our experiments prove that terahertz Time-Domain
Spectroscopy technique should be a powerful candidate for detecting atmospheric pollutants.
A terahertz time-domain spectrometer is employed to study various properties of jade, including the
kind identification and polarization analysis. The characteristic absorption spectra and refractive index
of jade are obtained in the range of 0.2 to 2.6 THz. Studying the absorption spectra and the
transmission temporal THz waveform with two peaks, which were confirmed to be coming from
ordinary and extraordinary beams, respectively, and result in fake absorption features. A practical ways
are suggested to remove the fake absorption features and therefore the real absorption spectra of jade
which accurately indicate the information of the samples can be obtained.
The terahertz(THz) fingerprint spectra of Ephedrine Hydrochloride and Papaverine Hydrochloride have been measured
using THz time-domain Spectroscopy (THz-TDS) system in the region of 0.2~2.6 THz. To explain the spectra, both
gas-phase simulation methods and solid-state simulation methods were performed in the efforts to extract pictures of the
molecular interior vibrational modes. By comparing the results of various gas-phase simulation methods, It was found
that using the semi-empirical theory is more applicable than the density functional theory (DFT) for some chemical
compounds. In the solid-state calculations, solid-state density functional theory (DFT) was employed to obtain the
vibration frequencies and Difference-Dipole Method (DDM) was used to calculate the corresponding infrared (IR)
intensity. In the process of calculating the IR intensity of Papaverine Hydrochloride in terahertz range, we found that the
results by Hirshfeld partitioning method agree better with the experiments than the ones derived from Mulliken atomic
charges. Moreover, the accuracy of simulation results depends on the basis sets and grid size being chosen.
Experimental measurement and theoretical analysis of THz spectrum for methylenedioxy amphetamine are introduced.
The refractive index and absorption coefficient of the sample were observed by terahertz time-domain spectroscopy
(THz-TDS) technique in the range of 0.2~2.6 THz. It exhibits obvious absorption feature at 1.40 THz and weak THz
absorption at around 1.68 and 2.21 THz. The spectral absorption characteristic in THz band was useful for the inspection
and identification of drugs using THz-TDS. The theoretical calculation was performed using Density functional theory
(DFT) with the GAUSSIAN 03 software package. Fully geometry optimization and frequency analysis of the optimized
structure were performed at the B3LYP/6-21G levels. The simulated absorption spectrum was in agreement with the
experimental data, and can hence be used for the assignment of observed THz spectrum. The theoretical simulation result
showed that absorption peaks mainly result from intra-molecule and inter-molecule vibrations, different absorption peaks
are corresponding to different vibrational modes and intensity. So the combination of the THz-TDS and DFT is an
effective way to investigate characteristic spectra of illicit drugs.
The applications of ultrasonic infrared thermal wave nondestructive evaluation for crack detection of several
materials, which often used in aviation alloy. For instance, steel and carbon fiber. It is difficult to test cracks interfacial or
vertical with structure's surface by the traditional nondestructive testing methods. Ultrasonic infrared thermal wave
nondestructive testing technology uses high-power and low-frequency ultrasonic as heat source to excite the sample and
an infrared video camera as a detector to detect the surface temperature. The ultrasonic emitter launch pulses of
ultrasonic into the skin of the sample, which causes the crack interfaces to rub and dissipate energy as heat, and then
caused local increase in temperature at one of the specimen surfaces. The infrared camera images the returning thermal
wave reflections from subsurface cracks. A computer collects and processes the thermal images according to different
properties of samples to get the satisfied effect. In this paper, a steel plate with fatigue crack we designed and a juncture
of carbon fiber composite that has been used in a space probe were tested and get satisfying results. The ultrasonic
infrared thermal wave nondestructive detection is fast, sensitive for cracks, especially cracks that vertical with structure's
surface. It is significative for nondestructive testing in manufacture produce and application of aviation, cosmography
A method was proposed to quantitatively inspect the mixtures of illicit drugs with terahertz time-domain spectroscopy
technique. The mass percentages of all components in a mixture can be obtained by linear regression analysis, on the
assumption that all components in the mixture and their absorption features be known. For illicit drugs were scarce and
expensive, firstly we used common chemicals, Benzophenone, Anthraquinone, Pyridoxine hydrochloride and L-Ascorbic
acid in the experiment. Then illicit drugs and a common adulterant, methamphetamine and flour, were selected for our
experiment. Experimental results were in significant agreement with actual content, which suggested that it could be an
effective method for quantitative identification of illicit drugs.
Absorption spectra in the range from 0.2 to 2.6 THz of chemicals such as illicit drugs and antibiotics obtaining
from Terahertz time-domain spectroscopy technique were identified successfully by artificial neural networks. Back
Propagation (BP) and Self-Organizing Feature Map (SOM) were investigated to do the identification or classification,
respectively. Three-layer BP neural networks were employed to identify absorption spectra of nine illicit drugs and six
antibiotics. The spectra of the chemicals were used to train a BP neural network and then the absorption spectra
measured in different times were identified by the trained BP neural network. The average identification rate of 76% was
achieved. SOM neural networks, another important neural network which sorts input vectors by their similarity, was used
to sort 60 absorption spectra from 6 illicit drugs. The whole network was trained by setting a 20×20 and a 16×16 grid,
and both of them had given satisfied clustering results. These results indicate that it is feasible to apply BP and SOM
neural networks model in the field of THz spectra identification.
The absorption spectra of two illicit drugs, methylenedioxyamphetarnine (MDA) and methamphetamine (MA), within
and without two conventional envelopes are studied using terahertz time-domain spectroscopy technique. The
characteristic absorption spectra of MDA and MA are obtained in the range of 0.2 THz to 2.5 THz. MDA has an obvious
absorption peak at 1.41 THz while MA has obvious absorption peaks at 1.23 THz, 1.67 THz, 1.84 THz and 2.43 THz. We
find that the absorption peaks of MDA and MA within the envelopes are almost the same as those without the envelopes
respectively although the two envelopes have some different absorption in THz waveband. This result indicates that the
type of illicit drugs in envelopes can be determined by identifying their characteristic absorption peaks, and THz
time-domain spectroscopy is one of the most powerful candidates for illicit drugs inspection.
Digital holography is a powerful imaging technology in which the reconstruction processing is accomplished via a computer and no wet processing is required. Therefore, it can obtain the image of an object in real time. Furthermore, both the amplitude and phase information of a wave front can be obtained simultaneously. In-line digital holography can effectively utilize the spatial-bandwidth product of the digital recorder, such as CCD or CMOS. Reconstruction algorithms allow a continuous development and expand the applications of the digital holography. In this presentation, a novel method will be presented for reconstruction of wave front from a series of in-line holograms. After determining the phase and amplitude distribution of the wave front at a given plane, the original object can be reconstructed via the inverse propagation. Due to no reference wave is required in this approach, the optical setup is relatively simplified, the size of the recording object can be enlarged, and the signal-noise-ratio of the system can be improved. The simulation results based on the Fresnel transform are presented to demonstrate the validity of this new approach. The image reconstructed from experimentally recorded holograms by using the Rayleigh-Sommerfeld approximation corresponds to the original object well.
In-line holography is a simple way for small object imaging. The Gabor transform is used for object characterization directly from in-line holograms. Three-dimensional locations of an object can be determined from the Gabor transform spectrum of its in-line hologram. The relationship between the Gabor angle and the location of the object is established, Computer simulations and experimental result have been presented to demonstrate the validity of this method for object charactering. The promising application of this method is particle field analysis.
We described an electro-optic detection technique-chirped-pulse cross correlation technique for measurement of an electron-beam bunch length. This is a high temporal resolution, single shot technique compared with the other two electro-optic detection techniques: the delay-scan method and the chirped-pulse spectrometer method. In delay-scan method temporal resolution is high, but measurement speed is not ideal. Although in the method of chirped-pulse spectrometer is single-shot with a high measurement speed, the temporal resolution is limited, which has been proved theoretically and experimentally. In chirped-pulse cross correlation technique, resolution and measurement speed are both satisfied. The technique is used to measure electron-beam bunch length in an accelerator.