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Terahertz transmission of several metallic mesh structures is studied based on the finite differential time domain (FDTD) method. The terahertz filtering properties of these metallic meshes are analyzed by the numerical simulation. The shape and size dependence of terahertz transmission of these metallic structures are illustrated. The numeric results show that the terahertz transmission of these metallic meshes have various frequency selectivity. The design of terahertz filters for the different resonance frequencies is presented based on the above simulation. This work provides a good reference for the design and manufactures of terahertz filter.

This paper presents the design and numerical simulation of the double H-shaped metallic periodic structure based on finite difference time domain (FDTD) method in terahertz frequency range. The double H-shaped structure unit cell consists of two H structures overlapped in the same plane. Numerical simulation results show that the double H-shaped structure results in a distinct and strong transmission trap in 0.2～3.0THz range. The position and the full wave at half maximum (FWHM) of transmission trap are changed with different structure size. The surface current distribution of structure is numerical simulated, which clarifies the frequency selection mechanism of the transmission spectra.

Optical limiting property of a novel molybdenum complex of fullerene C 70 , (η 2 -C 70 )Mo(CO) 2 ( o -phen)(DBM), was studied under irradiation of 10-ns laser pulse at 532 nm. The experimental results demonstrated that the derivative performed with better optical limiting behavior than the parent C 70 . An explanation based on the enhanced triplet–triplet absorption dominated by the intramolecular charge transfer was given.

The design optimization of buckling behaviour is studied for complex built-up structures composed of various kinds of elements and implemented within JIFEX95, a general-purpose software for finite element analysis and design optimization. The direct and adjoint methods of sensitivity analysis for critical buckling loads are presented with detailed computational procedures. Particularly, the variations of prebuckling stresses and external loads have been accounted for. The design model and solution methods presented in this paper are available for both shape and size optimization, and buckling optimization can also be combined with static, frequency and dynamic response optimization. The numerical examples show the applications of the buckling optimization method and the effectiveness of the methods and the program of this paper.

The novel cesium chloride-D-ribose complex (CsCl·C5H10O5; Cs-R) and cesium chloride-myo-inositol complex (CsCl·C6H12O6; Cs-I) have been synthesized and characterized using X-ray diffraction and FTIR, FIR, THz, and Raman spectroscopy. Cs(+) is eight-coordinated to three chloride ions, O1 and O2 from one D-ribose molecule, O1 from another D-ribose molecule, and O4 and O5 from the third D-ribose molecule in Cs-R. For one D-ribose molecule, the oxygen atom O1 in the ring is coordinated to two cesium ions as an oxygen bridge, O2 is cocoordinated with O1 to one of the two cesium ions, and O4 and O5 are coordinated to the third cesium ion, respectively. O3 does not coordinate to metal ions and only takes part in forming hydrogen bonds. One chloride ion is connected to three cesium ions. Thus, a complicated structure of Cs-D-ribose forms. For Cs-I, Cs(+) is 10-coordinated to three chloride ions, O1 and O2 from one myo-inositol molecule, O3 and O4 from another myo-inositol molecule, O5 and O6 from the third myo-inositol molecule, and O6 from the fourth myo-inositol molecule. One metal ion is connected to four ligands, and one myo-inositol is coordinated to four Cs(+) ions, which is also a complicated coordination structure. Crystal structure results, FTIR, FIR, THz, and Raman spectra provide detailed information on the structure and coordination of hydroxyl groups to metal ions in the cesium chloride-D-ribose and cesium chloride-myo-inositol complexes.

A. oryzae 3.042 (China) and A. oryzae RIB40 (Japan) used for soy sauce fermentation show some regional differences. We sequenced the genome of A. oryzae 3.042 and compared it to A. oryzae RIB40 in an attempt to understand why different features are shown by these two A. oryzae strains. We predict 11,399 protein-coding genes in A. oryzae 3.042. The genomes of these two A. oryzae strains are collinear revealed by MUMmer analysis, indicating that the differences are not obvious between them. Several strain-specific genes of two strains are identified by genome sequences' comparison, and they are classified into some groups, which have the relationship with cell growth, cellular response and regulation, resistance, energy metabolism, salt tolerance, and flavor formation. A. oryzae 3.042 showed stronger potential for mycelial growth and environmental stress resistance, such as the genes of chitinase and quinone reductase. Some genes unique to A. oryzae RIB40 were related to energy metabolism and salt tolerance, especially genes for Na(+) and K(+) transport, while others were associated with signal transduction and flavor formation. The genome sequence of A. oryzae 3.042 will facilitate the identification of the genetic basis of traits in A. oryzae 3.042, and accelerate our understanding of the different genetic traits of the two A. oryzae strains.

Salmonella typhiis a pathogen that causes the human disease of typhoid fever. The aim of this study was to investigate the viable but nonculturable (VBNC) state ofS. typhi. Some samples were stimulated at 4°C or −20°C, while others were induced by different concentrations of CuSO4. Total cell counts remained constant throughout several days by acridine orange direct counting; however, plate counts declined to undetectable levels within 48 hours by plate counting at −20°C. The direct viable counts remained fairly constant at this level by direct viable counting. Carbon and nitrogen materials slowly decreased which indicated that a large population of cells existed in the VBNC state and entered the VBNC state in response to exposure to 0.01 or 0.015 mmol/L CuSO4for more than 14 or 12 days, respectively. Adding 3% Tween 20 or 1% catalase enabled cells to become culturable again, with resuscitation times of 48 h and 24 h, respectively. The atomic force microscope results showed that cells gradually changed in shape from short rods to coccoids, and decreased in size when they entered the VBNC state. Further animal experiments suggested that resuscitated cells might regain pathogenicity.

The terahertz transmission characteristics of bilayer metallic meshes are studied based on the finite difference time domain method. The bilayer well-shaped grid, the array of complementary square metallic pill and the cross wire-hole array were investigated. The results show that the bilayer well-shaped grid achieves a high-pass of filter function, while the bilayer array of complementary square metallic pill achieves a low-pass of filter function, the bilayer cross wire-hole array achieves a band-pass of filter function. Between two metallic microstructures, the medium need to be deposited. Obviously, medium thicknesses have an influence on the terahertz transmission characteristics of metallic microstructures. Simulation results show that with increasing the thicknesses of the medium the cut-off frequency of high-pass filter and low-pass filter move to low frequency. But the bilayer cross wire-hole array possesses two transmission peaks which display competition effect.

Aspergillus oryzae is the most important fungus for the traditional fermentation in China and is particularly important in soy sauce fermentation. We report the 36,547,279-bp draft genome sequence of A. oryzae 3.042 and compared it to the published genome sequence of A. oryzae RIB40.

Aspergillus oryzae plays a central role in soybean fermentation, particularly in its contribution to the flavor of soy sauce. We present a comparative assessment of the intracellular differences between wild-type strain 3.042 and mutant strain A100-8, at the proteome level. 522 different protein spots were identified by MALDI-TOF MS, with 134 spots being confirmed by MALDI-TOF MS/MS. Of these, 451 were differentially expressed proteins (DEPs). There was at least a two-fold increase for 288 spots, and at least a two-fold decrease for 163 spots, in strain A100-8 when compared to 3.042. Further analysis showed that 63 of the more abundant proteins were involved in glycolysis and the citrate cycle; 43 more abundant proteins and 10 less abundant proteins were related to amino acid biosynthesis and metabolism; two of the more abundant proteins were involved in vitamin biosynthesis; and five of the more abundant proteins and four of the less abundant proteins were related to secondary metabolites. Moreover, quantitative real time PCR showed that the mRNA expression levels of six typical genes we selected were consistent with changes in protein expression. We postulate that there may be a relationship between DEPs and the flavor formation mechanism in A. oryzae.

The coordination of carbohydrate to metal ions is important because it may be involved in many biochemical processes. The synthesis and characterization of several novel lanthanide-erythritol complexes (TbCl(3)·1.5C(4)H(10)O(4)·H(2)O (TbE(I)), Pr(NO(3))(3)·C(4)H(10)O(4)·2H(2)O (PrEN), Ce(NO(3))(3)·C(4)H(10)O(4)·2H(2)O (CeEN), Y(NO(3))(3)·C(4)H(10)O(4)·C(2)H(5)OH (YEN), Gd(NO(3))(3)·C(4)H(10)O(4)·C(2)H(5)OH (GdEN)) and Tb(NO(3))(3)·C(4)H(10)O(4)·C(2)H(5)OH (TbEN) are reported. The structures of these complexes in the solid state have been determined by X-ray diffraction. Erythritol is used as two bidentate ligands or as three hydroxyl group donor in these complexes. FTIR spectra indicate that two kinds of structures, with water and without water involved in the coordination sphere, were observed for lanthanide nitrate-erythritol complexes. FIR and THz spectra show the formation of metal ion-erythritol complexes. Luminescence spectra of Tb-erythritol complexes have the characteristics of the Tb ion.

So far, the strong demand for non-destructive testing of adhesive bonds has not sufficiently been met. Here, we demonstrate the capability of terahertz time-domain spectroscopy as a non-destructive technique for the analysis of adhesive layers in terms of thickness and dielectric properties by inspecting three different material systems.

In this paper, the terahertz time domain spectroscopy (THz-TDS) technology is used to study the terahertz (THz) spectral characteristics of the Yungang Grottoes weathered material samples winch collected from No. 4, 9 and 39 these three different caves dug in different periods, A.D.520, A.D.494 and A.D. 484 years. The available effective wave band is between 0.2-2.6 THz. It is found that the transmission coefficient is high in low frequency region but low in high frequency region for all of the three kinds of samples. Experimental results also indicate that all of the samples have weak absorption in low frequency region, but the absorption coefficient increase quickly by exponential function as the frequency increasing. This character is more obvious especially for the absorption spectrum of the samples from the cave of late period. The refraction coefficient for the three kinds of samples has obvious differences in the whole THz wave band. The mean refraction coefficient of them is 1.53, 1.57 and 1.51 separately. According the results above, different periods of caves weathered samples can be identified. In addition, we can also offer the various optic constant of Yungang Grottoes samples in THz wave band for other studies work.

The transmission spectra of sub-wavelength cross metallic fractal slits in terahertz (THz) frequency region are presented by means of finite-difference-time-domain (FDTD) simulation. The transmission spectra with multiple pass bands and stop bands are observed. To understand the physical mechanism of the enhanced transmissions, we simulated the electric field distribution of THz radiation within the metallic slits at the resonance frequencies by the electromagnetic design software named CONCERTO. Further analysis reveals that the two transmission peaks in the low frequency is the local resonance of electric field of the two cross slit, respectively. The third transmission peak is the co-effect of the two level cross slits. Our simulation is helpful for the understanding of THz wave propagation and THz transmission through the cross metallic fractal structures. It is also useful for the development of THz photonic devices.

Terahertz time-domain spectroscopy (THz-TDS) is a new coherent spectral technique. The spectral characteristics of Acesulfame-K in the range of 0.2-2.6THz had been measured with THz-TDS. We obtained its transmission spectrum, refractive index spectrum and absorption spectrum at room temperature in the nitrogen atmosphere. The results show that Acesulfame-K had the abnormal dispersions at 0.40THz, 0.66THz, 0.94THz, 1.79THz and 2.30THz. The vibration absorption spectrum of single molecule of Acesulfame-K is simulated based on the Density Functional Theory (DFT). It is found that Acesulfame-K has the obvious absorbance in THz region. This result shows that THz-TDS has a potential application in the field of food security.

In this paper, the terahertz transmission properties of metallic fractal structures are presented by the terahertz time domain spectroscopy and the numerical analysis based on the finite differential time domain simulation. Several metallic fractal structures including the H-shape fractal pattern and the square-hole fractal pattern are studied. The terahertz transmission spectra of these metallic fractal structures are shown at two polarization of terahertz field perpendicularly. The results show that the asymmetric metallic fractal structures such as H-shape fractal structure have an obvious polarization dependent and frequency selective transmission. The symmetric structures have no such polarization dependence. Terahertz transmission through the H-shape metallic fractal structure can be switched between the different pass bands by changing the polarization direction of terahertz field relative to the first-level fractal line. Therefore, a potential application may be to realize a polarization tunable terahertz filter based on this kind of H-shape metallic fractal structure.

SrB 4 O 7 (SBO) is a promising nonlinear optical crystal. It has the orthorhombic structure with group classified as Pnm2. The sample for the experiment was cut along the (001) plane and twin polishing with 1.632mm thickness. It exhibits a wider transparency range from UV to far-IR. And its absorption edge lies at 160nm. The forbidden band gap is about 7.76eV. The THz spectra of SBO crystal had been studied from 0.1 to 2.5THz. The THz time domain spectrum of SBO shows the strong resonance characters. In THz experiment, the vertical incident electromagnetic waves radiate the polished side twice along (001) orientation. The crystal turned 90 degrees relative to the first in the vertical direction. There are different optical properties in two directions. We gained the curves of the refractive index and absorption coefficient dependence of frequency in the region of 0.1-2.5THz. The absorption curves shows opposite parabola character. One is upward opening and the largest absorption coefficient is 10cm -1 . The other is down opening and the less absorption coefficient is 1cm -1 . The refractive index n is stable linear with frequency and it is 3 from 0.4THz to 2.5THz. But the refractive index of two directions shows the opposite tendency from 0.1 to 0.4THz. The reason of the difference is that polarized beam radiates the orthorhombic crystal. The properties of the sample show that it is possible to apply it to laser field.

THz time domain spectra of Bi 4 Ge 3 O 12 (BGO) crystal were measured. The refractive index and power absorption function and optical dielectric function were obtained. The time domain spectrum shows resonance characteristic. There was one strong absorption band in the range of 1.5–2.3 THz. And the refractive index exist abnormal dispersion in the range. The time domain spectra characteristic of photon-phonon interaction were presented and it show that the phonon polariton arises in BGO crystal.

We have performed a large set of spectroscopic measurements on a set of material samples and metal mesh grids with a THz Fourier transform spectrometer and two THz Time domain spectrometers. We used the statistical nature of the measurements from their repeatability and compared the results for the two different spectroscopic techniques. We find that the two systems are roughly equivalent with functional differences related to the frequencies of operation.

A new effective method for computing the acoustic radiation and its sensitivity analysis of a structure subjected to stochastic excitation is presented. Previous work in the area of structural and acoustic sensitivity analysis systems was mostly focused on the deterministic excitation. New methods are developed to account for stochastic excitation. The structural-acoustic response is calculated using finite element method and boundary element method combined with stochastic analysis techniques. An accurate and highly efficient algorithm series for structural stationary random response analysis, pseudo-excitation method (PEM), is extended to acoustic random analysis in this paper, which was used to calculate structural random analysis in the past. So the acoustic radiation problems of random responses are transformed to the structural-acoustic harmonic analyses. This is a time-saving progress in comparison with traditional method. Based on the PEM, the acoustic radiation sensitivities of the structure are developed in emphasis that are transformed to harmonic sensitivity analyses. They are validated by comparing with the results of finite difference sensitivity method. Numerical examples are given to demonstrate the effectiveness of the methods and the program.

THz emission characteristics of the low-temperature grown GaAs photoconductive antenna under the various types of biased electrical fields are investigated. The biased electric fields including DC (direct current) and AC (sine wave and square wave) are applied on the antenna to reveal the evolution of THz wave. At the condition of effective voltage kept as same and the various frequencies lied between 1 kHz and 9 kHz, we confirmed that the optimized frequency of the biased electrical field is 6 kHz for the sine wave and square wave, respectively. For the case of same effective voltage or biased electric field, the experimental results show that THz signal generated by the sine wave is more efficient than the DC and square wave; this is attributed to the sine wave with higher amplitude of biased electric field. Whereas the experimental results show that the intensity and the signal-to-noise ratio of the THz radiations generated by the square wave are stronger than that of sine wave under the same amplitude of biased electric field, this is caused by the higher effective voltage for the square wave. Therefore, our results indicate that the frequency and type of biased electric fields take an important effect on the intensity and signal-to-noise ratio of the generated THz radiations.

The enhanced transmission spectra and reflection spectra of sub-wavelength fractal structure named Sierpinski fractal structure are presented by means of finite-difference-time-domain (FDTD) simulation. It is found that there are several transmission peaks in the transmission spectra and several reflection peaks in the reflection spectra. The transmission peaks appears red shift and increases with increasing of side length of center square holes when keeping the period of array as a constant. To investigate the physical mechanism of the enhanced transmissions, we simulated the incidence and transmission of THz radiation field at certain transmission peak and show the propagation and distribution of the interior electromagnetic field by the electromagnetic design software named CONCERTO. It is found that different transmission peaks are caused by the different level of square holes. Further analysis reveals that the transmission enhancement is from the interaction of the complicated waveguide coupling effect and the local resonance of electric field. Our simulation is helpful for the understanding of THz wave propagation and THz transmission through the fractal structures of the metal foil.

Gallic acid is natural polyphenol compound found in many green plants. More and more experiments have demonstrated that the gallic acid has comprehensive applications. In the field of medicine, the gallic acid plays an important role in antianaphylaxis, antineoplastic, antimycotic, anti-inflammatory, antivirotic, antiasthmatic and inhibiting the degradation of insulin. It also has a lot of applications in chemical industry, food industry and light industry. So it is important to study the terahertz time-domain spectroscopy of gallic acid. Terahertz time-domain spectroscopy (THz-TDS) is a new coherent spectral technology based on the femtosecond laser. In this work, the spectral characteristics of gallic acid in the range of 0.4 THz to 2.6 THz have been measured by THz-TDS. We obtained its absorption and refraction spectra at room temperature. The vibration absorption spectrum of the single molecule between 0.4 THz and 2.6 THz is simulated based on the Density Functional Theory (DFT). It is found that the gallic acid has the spectral response to THz wave in this frequency range. The results show the abnormal dispersion at 1.51 THz and 2.05 THz. These results can be used in the qualitative analysis of gallic acid and the medicine and food inspection.

The absorption and refractive index of ellagic acid in the range of 0.2–2.4 THz have been measured by THz-TDS. It is found that the ellagic acid has the fingerprint absorption in this frequency region. The vibration absorption spectrum of the single molecule of ellagic acid between 0.2 and 2.4 THz is simulated based on the Density Functional Theory (DFT). THz absorption at low frequencies is attributed to the vibration absorption of water of crystallization. The results presented in this paper will be helpful for the inspection of medicine and food.

In this paper, the propagation characteristics of THz wave through two-dimension photonic crystals of square lattices are studied. The band structures of photonic crystals are calculated by means of the plane wave expansion (PWE) and the self-compiled MATLAB program. It is found that when lattice constant is the scale of sub-millimeter, the periodic dielectric with air cylinders in silicon (e =11.9 ), gallium arsenide (e =13.6 ), and germanium (e =16.0 ) matrix can generate the absolute photonic band-gaps (PBG) at terahertz frequencies. The larger photonic band-gap can be obtained by increasing the difference of dielectric constant properly. The relation between the maximum PBG and the filling ratio for germanium with the larger PBG is given. These results provide theoretical guide for the development of THz waveguide devices.

The terahertz (THz) emission properties of four kinds of bow-tie photoconductive antennas are studied. The characteristic of THz radiation generated by them is compared. The emission spectra of the photoconductive antennas are obtained by THz time domain spectroscopy (TDS) technology. The corresponding frequency domain spectra are obtained by Fast Fourier Transformation (FFT). The results show that when we increase the bias voltage, the peak value of THz radiation is increased and tends to saturation when the pump power is strong enough. Under the same bias voltage and the pump power, the properties of THz radiation generated by four bow-tie photoconductor antennas are compared. It shows that under low bias voltage, the full width of half maximum (FWHM) of frequency a domain spectrum which is generated by small-aperture bow-tie photoconductor antenna is broader than that of the large aperture one. The gap size of small-aperture photoconductive antenna is smaller, the FWHW is broader. On the other hand, under the high bias voltage, the intensity of THz radiation of the large aperture photoconductor antenna is much larger than the small aperture one. Our results provide a reference to investigate and fabricate the high efficient of THz emission source.

In this paper, the imaging ability of terahertz wave in time-domain spectroscopy (THz-TDS) imaging system is assessed by using the step-by-step scan imaging method to four small structures: thread, dots, round hole, and square on the focus of the imaging system. We utilize THz-TDS energy imaging model to acquire the energy distribution of terahertz wave passing through the different small structure, which can be use as a criterion of imaging ability. Theoretically, terahertz imaging technology possesses highly spatial resolution because the size of spot is inversely proportional to the frequency. Our experimental results also show that THz-TDS technology has a preferable spatial resolution on the millimeter scale. In addition, a more delicate and smooth image can be obtained by means of the nearest neighbor interpolation algorithm. A method to measure the size of target is provided. These results are important references for the further terahertz spectroscopy imaging research.

Beam profile and spectral characteristic of terahertz (THz) wave in free space are presented in this paper. The beam width of THz wave at the focus point of parabolic mirror is obtained by means of the narrow-slit measurement. By the spectroscopic imaging, we present the transverse mode distribution of THz beam on the cross-section of focus point. Our experimental results show that the centre wavelength of THz spectra has a distinguished red-shift when it is far away the centre of THz focus point. The spectral range of THz wave far from the focus point is less than that of the centre. This kind of spectral characteristic of THz wave is closely related to the diffraction effect of electromagnetic wave.

We present the enhanced transmission spectrum of a copper foil with the sub-wavelength fractal structures by means of the terahertz time domain spectroscopy (THz-TDS) and FDTD simulation. In the view of experimental measurement and finite-difference-time-domain (FDTD) simulations, respectively, we studied the influence of the electric field and magnetic field on the enhanced transmission of THz wave through each level of fractal pattern generated by the repeated affine transformations of an H-shaped mother element on the copper foil. We simulate the incidence and transmission of the THz wave and show the propagation and distribution of the interior electromagnetic field by the software for electromagnetic design named CONCERTO. To compare with the experimental results, we simulate the cases that the certain levels of the pattern are deleted. The results of simulation agree with the experimental one. It is found that the transmission enhancement in the low frequency regime is caused by the radiation of electron resonance in the low fractal levels, and the transmission enhancement in the high frequency regime is caused by the radiation of electron resonance in the high fractal level, that is, the localization resonance of the fractal structures. These results indicate that the flat surface fractal structure like an ideal wave-guide. The vertically incident THz wave is confined on the surface and transmitted along the fractal slits. The controlling ability of fractal structures will offer a powerful tool for the design of THz photonic devices.

Experimental measurement and theoretical analysis of THz vibration spectra of four different kinds of vitamins are presented. The refractive index and absorbance of these vitamins are measured at room temperature by THz-TDS in the frequency region of 0.2-2.6 THz. The full-geometry optimizations and frequency calculations using the density functional theory (DFT) are applied to obtain the structure and vibration frequencies of these vitamins. The calculated results are in agreement with the experimental data. The simulation results show that the intermolecular interactions are considerably weak so that the gas-phase simulations spectra are closely to the solid-phase. The calculated results confirm that most of the absorption peaks result from the intra-molecular modes; the others have been ascribed to intermolecular interaction or phonon modes.

In this paper several polycrystalline molecules with sulfonate groups and some of their metal complexes, including DL-homocysteic acid (DLH) and its Sr- and Cu-complexes, pyridine-3-sulphonic acid and its Co- and Ni-complexes, sulfanilic acid and L-cysteic acid were investigated using THz time-domain methods at room temperature. The results of THz absorption spectra show that the molecules have characteristic bands in the region of 0.2-2.7 THz (6-90 cm(-1)). THz technique can be used to distinguish different molecules with sulfonate groups and to determine the bonding of metal ions and the changes of hydrogen bond networks. In the THz region DLH has three bands: 1.61, 1.93 and 2.02 THz; and 0.85, 1.23 and 1.73 THz for Sr-DLH complex, 1.94 THz for Cu-DLH complex, respectively. The absorption bands of pyridine-3-sulphonic acid are located at 0.81, 1.66 and 2.34 THz; the bands at 0.96, 1.70 and 2.38 THz for its Co-complex, 0.76, 1.26 and 1.87 THz for its Ni-complex. Sulphanilic acid has three bands: 0.97, 1.46 and 2.05 THz; and the absorption bands of l-cysteic acid are at 0.82, 1.62, 1.87 and 2.07 THz, respectively. The THz absorption spectra after complexation are different from the ligands, which indicate the bonding of metal ions and the changes of hydrogen bond networks. M-O and other vibrations appear in the FIR region for those metal-ligand complexes. The bands in the THz region were assigned to the rocking, torsion, rotation, wagging and other modes of different groups in the molecules. Preliminary assignments of the bands were carried out using Gaussian program calculation.

Absorption coefficient epsiv(nu) and dielectric coefficient epsiv(nu) of crystal Cr3+:LiSrAlF6 were obtained by THz time domain spectroscopy (THz-TDS) in the range of 0.2-1.2THz. The infrared transmission spectrum R(kappa) was measured from 6.7 cm-1(0.2 THz) to 4000 cm-1. There is a band of the phonon absorption in the crystal. The frequency omegaLO of the longitudinal optical phonon model LO is about 236 THz. And the omegaTO of the transverse optical phonon model TO is about 9.42 THz.

THz time domain spectrum of KH2PO4 crystal has been measured in the range from 0.2 THz to 1.6 THz. Ultraviolet-visible-infrared spectra have been measured in the range from 190 nm to 1600 nm at the room temperature. The energy band gap Eg of KH2PO4 crystal is 5.90 eV. There is a wide band of the phonon absorption in the KDP crystal. The frequency omegaLO of the longitudinal optical phonon model LO is about 1.29times1015 Hz. Frequency omegaTO of the transverse optical phonon model TO is about 6.28times1012Hz.

As a new technology, the terahertz technology had made a great progress in security inspection and medical field. This paper shows the application of the terahertz time-domain spectroscopy (THz-TDS) technology on cosmetic testing. We obtain the THz spectra of three kinds of usual cosmetics powders. Two kind of powder have an obvious absorption peak at 1.14 THz, but the third one has no absorption peak. The positions of absorption peaks in the infrared spectra of three kinds of powders are approximately identical. These results show that THz-TDS technology has the advantage and potential application on the cosmetic testing. In addition, we also measure some solid and liquid cosmetic components, such as Titanium-dioxide, Magnesium Stearate, Kaolin, Glycerol, etc. THz spectra of their refractive index and absorption coefficient are obtained experimentally. We are trying to establish the fingerprint spectra database of cosmetic components for further research and application.

In this paper, we present experimentally the transmission properties of THz pulse through subwavelength planar fractal slits on the copper foil. The transmission measurement is carried out using THz time-domain spectroscopy. THz spectroscopy of these fractal slits shows the featured frequency selectivity. Multiple band gaps and pass bands for THz wave are observed. THz transmission under different polarization for a 7-level fractal pattern is analyzed. The transmission spectra with the different levels of fractal slits are compared and discussed. Polarization dependent THz transmission is attributed to the localized resonance induced by the fractal pattern.

We experimentally investigate the resonantly enhanced transmission of the terahertz radiation through a periodic array of subwavelength apertures on metal films. We fabricated the periodic arrays of subwavelength apertures with different periods and different diameters on silicon substrate. THz transmission spectra of these samples are measured by means of terahertz time-domain spectroscopic system. The resonantly enhanced transmissions with the frequency selectivity are observed. Our experimental results show that the resonantly transmission peak appears red shift and increases with increasing of hole diameter when keeping the period of array as a constant. On the other hand, the resonantly transmission peak with the same hole diameter appears red shift with increasing of the array period.

In the terahertz (THz) spectroscopic system, the research of propagation characteristics of terahertz electromagnetic field is very important. Using a single slit which width is close to the central wavelength of terahertz pulse, we investigate the spectral distribution of terahertz beam at the location of samples. We obtain the following results by analyzing the experimental data. Firstly, the size of THz beam is different for the THz wave of the different frequency. The width of THz beam is small for the high frequency of THz radiation. At the same frequency, THz beam becomes wider for the narrower slit, that is, THz wave show the obvious diffraction phenomenon. Secondly, the frequency spectra distribution is different at the different position of THz beam. The peak position of frequency spectra appears red shift with the increasing of the distance away from the center of terahertz beam. These results provide an important reference for the further terahertz experiments of spectroscopy and imaging.

We experimentally investigated the polarization dependence of enhanced transmission of terahertz radiation through the periodic array of sub-wavelength rectangle holes. The array patterns of rectangle holes are fabricated by the cutting of YAG laser to the copper foils with 100 mum thickness. These patterns are designed as different sizes and different shapes of rectangular holes on the copper foils. The optical transmission properties in terahertz range are obtained by measuring terahertz time-domain spectra of these samples. Our results show that the transmission of periodic array of sub-wavelength rectangular holes proposes distinct frequency selectivity. The transmission peaks at the lower frequency increase with increasing of the angle of incident THz wave polarization relative to the long side of rectangle hole. The frequency locations of the transmission peaks do not change when the polarization of incident THz wave change. Our experimental results are going to be a important reference for developing photonic devices of THz frequency range.

We have built up two sets of THz generation and detection system. One uses the photoconductor antenna as the THz emitter, which can generate a stronger THz electromagnetic radiation. Its spectral range is relative narrow 0.1 - 1.1 THz, so it is suitable to the application of THz imaging. Another uses a femto-second laser pulse to excite semiconductor surface and generates the broadband THz radiation with the spectral range between 0.2 THz and 3.0 THz, which is suitable for the study on THz time resolved spectroscopy. Both of the THz setups utilize the detection technology of free-space electro-optic sampling, and realize the experimental function of low noise, high sensitivity high signal-to-noise ratio and very large of dynamical range. The signal-to-noise ratio of our system achieve at above 600. The dynamical range is 10 4 . Therefore, our setup provides a strong experimental basis for THz spectroscopy and imaging, and is ready to study on the application of THz optics, THz chemistry, material science, biology and medicine.

Terahertz (THz) emission properties of p-InAs surface radiation under the different excitations of femtosecond pulses are studied by means of time-domain spectroscopy. The experimental results show that the spectral waveform and amplitude of terahertz radiation are different for the excitations with different wavelengths. The full-width of half-maximum (FWHM) of THz radiation excited by the short wavelength of pulse is larger than that of the long wavelength. THz emission strength increases with increasing of pump wavelength. The peak amplitude of THz pulse increases linearly with increasing of the excitation power. It provides a useful reference for the application of THz emitter.

Low-temperature-grown GaAs (LT-GaAs) of 1-um thickness was grown at 250degC on semi-insulating GaAs (001) substrate using EPI GEN-II solid-source MBE system. The sample was then in situ annealed for 10 min at 600degC under As-rich condition. THz emitters were fabricated on this LT-GaAs with three different photoconductive dipole antenna gaps of 1-mm, 3-mm, and 5-mm, respectively. The spectral bandwidth of 2.75 THz was obtained with time domain spectroscopy. It is found that THz emission efficiency is increased with decreasing antenna gap. Two carrier lifetimes, 0.469 ps and 3.759 ps, were obtained with time-resolved transient reflection-type pump-probe spectroscopy.

THz wave imaging is a new and promising technology for material distinguishing and non-destructive testing. The processing of the time domain waveform acquired at each pixel of the image is one of the most important aspects of the THz imaging. Due to the diversity of samples in the practical applications, signal processing approaches are quite different. A good method permits high quality of the images. In the previous papers, some methods have been adopted to generate the image of the object; however, these methods have not been compared, and the reason for choosing certain approach has not been given. Therefore, it is very important to discuss the difference of different imaging approaches for a sample and to choose the best one. In this presentation, several data processing methods for terahertz transmitted spectral imaging based on classical transmitted scanning imaging setup and the Fourier transform, including time-domain maximum-amplitude (minimum-amplitude) imaging, time-domain peak-to-peak amplitude imaging, time-domain time delay imaging, frequency-domain fixed frequency amplitude (power) imaging, as well as frequency-domain fixed frequency phase imaging, are discussed and compared. The results indicate that the imaging quality is different for different approaches; furthermore, the optimal imaging methods for the samples used in this paper are also different.

Optical transmission properties of subwavelength planar fractals in terahertz (THz) frequency region are studied by means of time-domain spectroscopy. The transmission spectra with multiple pass bands and stop bands are observed. The tunable photonic band gaps are realized by changing the angle between the principle axis of planar fractal and the polarization of THz wave. The possible application of the subwavelength optical component is discussed. We attribute the detected transmittance from subwavelength fractals to localized resonance.

In this paper, a sub-layer design variable method is proposed to the design optimization of composite laminate plate structures. With this method, the laminated plate is divided into several sub-layers and each sub-layer is composed of some plies, which have the same thickness and orientation angles. The direct design variables of optimization are the thickness and angle of the sub-layers. This sub-layer variable method meets the requirement of practical design. The objectives and/or constraints include structural weight, displacements, free-vibration frequencies, and buckling critical load. The accurate sensitivity analysis is performed in detail, and the optimization of asymmetric laminate plate is also available. It should be noticed that the centerline of the laminated plate changes with the variation of the thickness of sub-layers. This aspect has been considered to maintain the accuracy of sensitivity analysis and process the design optimization of asymmetric laminated plates. The Sequential Linear Programming (SLP) or the Sequential Quadratic Programming (SQP) algorithms are employed in the optimization solution. The methods proposed in this paper have been implemented in the software JIFEX of the finite element analysis and design optimization of general purposed structures and applied to the problems of the static, buckling, and vibration optimization of composite laminate structures. The numerical examples are given to demonstrate the validation of algorithms and program.

We report the growth of a-plane InN on an r-plane sapphire substrate by plasma-assisted molecular-beam epitaxy. It is found that the a-plane InN is successfully grown by using a GaN buffer layer, which has been confirmed by reflection high-energy electron diffraction, x-ray diffraction and Raman scattering measurements. The Hall effect measurement shows that the electron mobility of the as-grown a-plane InN is about 406 cm2 /Vs with a residual electron concentration of 5.7 × 10 cm−3. THz emission from the a-plane InN film is also studied, where it is found that the emission amplitude is inversely proportional to the conductivity.