We have suggested a wide range of real-life applications using novel terahertz imaging techniques. A high-resolution terahertz tomography was demonstrated by ultra short terahertz pulses using optical fiber and a nonlinear organic crystal. We also report on the thickness measurement of very thin films using high-sensitivity metal mesh filter. Further we have succeeded in a non-destructive inspection that can monitor the soot distribution in the ceramic filter using millimeter-to-terahertz wave computed tomography. These techniques are directly applicable to the non-destructive testing in industries.

Terahertz wave (THz, also name T-Ray) belongs to far-infrared electromagnetic radiation. Since its unique properties, THz techniques have been paid more and more attentions during the past decades. In this field, THz digital holography is an important research branch, which can accurately extract three-dimensional optical information of objects. Based on features of this technique, it greatly reduces the experimental time and clearly presents the diffraction phenomena of the transmitted THz waves. We elucidated our works about the THz digital holography in recent years. Some key techniques in the THz digital holography are selected as research objects, which are the reflection measurement, quasi-near-field measurement, balanced electro-optic (EO) imaging, and polarization detection. From these four aspects, including the measurement mode, improvement of the spatial resolution, optimization of the signal to noise ratio (SNR), and acquirement of the polarization information, the THz digital holography imaging system has been investigated experimentally and theoretically. These works enhance the performances of the system and promote the practicability of the THz digital holography. Although there are a lot of theoretical and technical difficulties to be overcome in the practical applications, it is firmly believed that the THz digital holography will present strong abilities in factory and research fields in the future.

Quantitative measurement based on THz absorption spectrum is of great importance in THz applications. Several researchers have worked on it and gained some achievements, but most of them explored pure component or no more than 2-component s samples. In this paper, a mixture sample consisting of Glutamine, Histidine and Threonine is investigated in the frequency range from 0.3 to 2.6 THz. The quantitative measurement principle is the Lambert-Beer's Law which have been accepted in infrared and visible spectra. Our experiments show the validation of the law in THz region. A Least-Mean-Square algorithm is adopted and measurement errors of Glutamine, Histidine and Threonine are 17.60%, 4.44% and 2.59%.

The key point to measure a sample and to carry out its absorption spectrum is that the whole test process is completed in very stable situations. Although the distributed setup of THz-TDS is flexible to implement kinds of experiments, slightly displacements of mirrors may occur in the system. A typical kind of disturbance exists in the system due to shifts of mirrors and accumulation of static charges in THz switch or detector, particularly in a long term test. The resulting of the disturbance is that a deviation is involved in the THz pulse. Furthermore, due to the sample and reference can't be tested simultaneously, the sample's absorption spectrum maybe goes down to negative values at some frequencies. A recovery algorithm is presented to overcome the disturbance. Some examples validate the effects of the algorithm.

In the past decade, spectroscopy and imaging in the terahertz region (0.1-10 THz) of the electromagnetic spectrum has been applied in both basic research and potential industrial applications, such as medical diagnosis, security screening, radio astronomy, atmospheric studies, short-range indoor communication, chemical, biological sensing, medical and biological imaging, and detection of explosives. In this paper, we design a narrow bandpass terahertz wave filter using three kinds of two-dimensional photonic crystals. By using finite-difference time-domain (FDTD) method, we examined the transmittance spectra for the proposed terahertz wave filter. The simulated results show that the proposed filter exhibit excellent transmission performance such as high transmission at the central frequency, adjustable bandpass, and good rejection of the sideband frequencies.

We briefly review the key technology of modern fiber based femtosecond laser sources summarizing advantages and disadvantages of different mode-locking solutions. A description of possible extensions of a FemtoFiber-type modelocked Er-doped fiber laser oscillator (1560 nm) reveals the flexibility with respect to wavelength coverage (488 nm .. 2200 nm) and pulse duration (10 fs .. 10 ps). The resulting FemtoFiber family and its versions for instrument integration allow one to use these state-of-the-art light sources in many important applications, e.g. THz spectroscopy and microscopy. We show that, depending on the fiber laser model and the THz emitter, THz radiation can be produced with 4-10 THz bandwidth and detected with up to 60 dB signal-to-noise ratio (SNR). Electronically controlled optical scanning (ECOPS) - a unique method for fast, precise and comfortable sampling of the THz pulse or other pump-probe experiments - is described and recommended for efficient data acquisition. As examples for modern microscopy with ultrafast fiber lasers we present results of two-photon fluorescence, coherent microscopy techniques (SHG/THG/CARS) and fluorescence lifetime imaging (FLIM).

Experimental studies on a tunable efficient high-efficient pulsed NH₃ terahertz (THz) lasers pumped by TEA CO₂ lasers are presented. When NH₃ is pumped by the different lines with the CO₂ lasers, the generation of different terahertz radiations is discussed. The lines of the CO₂ lasers are 9R(08), 9P(20), 10R(14), 10R(08), and 10R(06). To improve THz laser energy and photon conversion efficiency, different higher power of the CO₂ laser can effectively improve THz laser energy and photon conversion efficiency. When the 9P(20) CO₂ lasers with 9.68 J and 4.12 J pump NH₃, the corresponding energy conversion efficiencies are 0.28% and 0.19%, increasing by a factor of about 1.5. The generation of terahertz radiations with energy as high as 27.29 mJ and 7.73 mJ are obtained, respectively, increasing by a factor of about 3.5. Meanwhile, for 10R(14) line, the energy conversion efficiencies increase to 8.5 times and the energy of THz lasers increase to 32 times.

The experiment collected some spinach leaves which were irradiated by pulsed CO₂ laser with energy 5.6J, 8.0J and 9.5J respectively. Each of them was soaked in three kinds of solvents (water, ethanol, the mixture of ethanol and petroleum ether) respectively. The experiment shows that the ethanol solution which contains the irradiated leaves turn dark green than the ethanol solution which contains the intact leaves and the color of solution with the leaves irradiated by CO₂ laser with 9.5J changes the most significantly. Further, selective excitation on the molecular level of the cell wall were used to explain the phenomenon.

One polarization measurement technology is proposed to apply in the basic Terahertz time domain spectroscopy (THz- TDS) using only one rotatable polarizer. The method to upgrade such a polarimetric Terahertz time-domain Spectroscopy (P-THz-TDS) was presented. The method is verified by measured important polarization parameters including Stokes parameters, polarization dependent loss, and birefringence of materials.

A switchable multi-wavelength Erbium-doped photonic crystal fiber (ED-PCF) ring laser based on a length of polarization-maintaining photonic crystal fiber(PM-PCF) is presented and demonstrated experimentally. A segment of ED-PCF is used as linear gain medium in the resonant cavity. Due to the polarization hole burning (PHB) caused by the PM-PCF and a polarization controller (PC), the laser can operate in stable dual- or triple- wavelength modes at room temperature. The optical signal-to-noise ratio (OSNR) of the laser without any wavelength-selective components is greater than 30 dB. The amplitude variations of lasing peaks in ten minutes are less than 0.26dB for two different operating modes.

Over the past ten years, electromagnetic terahertz (THz) frequencies region from 100 GHz to 10 THz (or wavelengths of 30μm-3mm) have received extensive attention and investigation. Terahertz wave detection enables direct calculations of both the imaginary and the real parts of the refractive index without using the Kramers-Kronig relations. There are many potential applications such as radio astronomy, atmospheric studies, remote sensing, and plasma diagnostics. Photonic crystal (PC) is a low-loss periodic dielectric medium. With special design and construct the PCs can control the propagation of THz wave in certain directions with specified frequencies. In this letter, we present the numerical design and analysis of three kinds of compact terahertz wave beam splitter based on photonic crystals structure. The novel terahertz wave polarizing beam splitter has been designed and calculated through finite element method. The simulation results show that the proposed polarizing beam splitter has high efficiency and a high extinction ratio. We confirm theoretically that the photonic crystal structures can be used for separating TE and TM-polarized modes of the electromagnetic waves in the terahertz range.

There are increasing demands for experiments in terahertz frequencies, in different areas such as biotechnology, nanotechnology, space science, security, terahertz wave communications, and plasma diagnostics. For potential applications, the functional devices, such as beam polarizers, modulators and filters, are crucuial components for a terahertz system. As a dispensable device for ultrafast information processing and interconnection of terahertz wave communication, terahertz wave filter has attracted considerable attention. In this paper, we design the terahertz wave filter structure based on three kinds of photonic crystals structures. The finite-difference time-domain (FDTD) has been employed to analysis the performances of these terahertz wave filters. The simulation results show that these designed filters exhibit excellent transmission performance such as high transmission at the central frequency, adjustable bandpass, and good rejection of the sideband frequencies. Three kinds of compact and integrated terahertz wave filters are obtained.

Terahertz radiations, which refer to the frequencies from 100GHz to 10THz, lie in the frequency gap between the infrared and microwave, have received considerable attention during the past decades. Due to their special prosperties, THz radiations have been applied in many fields such as gases, semiconductors, explosives materials, and environment pollutants. The technique is based on recording the time dependence of the electric field of a short electromagnetic pulse transmitted through a sample. The ratio of the Fourier transforms of the data recorded with and without the sample yields the complex transmission coefficient of the sample in the frequency domain. The absorption coefficient and the refractive index of the material studied are directly related to the amplitude and phase respectively of the transmitted field. Terahertz wave filter, a frequency-selective surface structure, has been characterized by terahertz time-domain spectroscopy in the region from 0.1 to 3THz. We have compared THz-TDS measurement and calculation results of the mode-matching theory of the terahertz wave filter, and find that the two data sets agree very closely. The peak of the transmittance of about 90.5%occurs at 0.45THz for the first case and the peak of the transmittance of about 89.4% occurs at 0.79THz for the second case.

Pulsed THz time-domain spectroscopy is a coherent technique, in which both the amplitude and the phase of a THz pulse are measured. Recently, material characterization using THz spectroscopy has been applied to biochemicals, pharmaceuticals, polymers and semiconductors and has given us important information. Moreover, THz imaging has progressed and is expected to be applicable for the identification of narcotics and explosives. The most important and characteristic point of THz spectroscopy is said to be its ability to observe intermolecular vibrations in contrast to infrared spectroscopy (IR), which observes intramolecular vibrations. Coherent detection enables direct calculations of both the imaginary and the real parts of the refractive index without using the Kramers-Kronig relations. Terahertz wave spectroscopy has been used to study the properties and absorption spectra characteristic of materials. In this paper, the spectral characteristics of cow skin, pig skin sheep skin, horse skin and deer skin have been measured with terahertz time-domain spectroscopy in the range of 0.1~2.0THz. The results show that THz-TDS technology provides an important tool for quality analysis and detection of leathers.

Terahertz wave is a kind of electromagnetic wave ranging from 0.1~10THz, between microwave and infrared, which occupies a special place in the electromagnetic spectrum. Terahertz radiation has a strong penetration for many media materials and nonpolar substance, for example, dielectric material, plastic, paper carton and cloth. In recent years, researchers around the world have paid great attention on terahertz technology, such as safety inspection, chemical biology, medical diagnosis and terahertz wave imaging, etc. Transmission properties of two-dimensional metal microstrip structures in the terahertz regime are presented and tested. Resonant terahertz transmission was demonstrated in four different arrays of subwavelength microstrip structure patterned on semiconductor. The effects of microstrip microstrip structure shape were investigated by using terahertz time-domain spectroscopy system. The resonant terahertz transmission has center frequency of 2.05 THz, transmission of 70%.

The terahertz (THz) band, which refers to the spectral region between 0.1 and 10THz, covers the fingerprints of many chemical and biological materials. Within the past few years, there are increasing demands for experiments in terahertz frequencies, in different areas such as biotechnology, nanotechnology, space science, security, chemical and biological sensing, terahertz wave communications, and medical diagnostics. For potential applications, the functional devices, such as beam polarizers, switchs and filters, are crucial components for a terahertz system. Terahertz wave filter based on two kinds of microstrip resonant structures, has been characterized by terahertz time-domain spectroscopy in the region from 0.1 to 3THz. The experimental results for the frequency dependence of the transmittance of the terahertz wave filter show that the terahertz wave transmittance peak is of 79.5% at 0.5THz and 82.5% at 0.81THz.

With the realization of terahertz wave generator and detector, electromagnetic terahertz wave wavelength range (30μm~3000μm) attracted significant attention and has been extensively investigated. Many potential applications of terahertz waves have been dramatically explored including medical diagnosis, security screening, military detection, radio astronomy, atmospheric studies, and communication. In this paper, we proposed a kind of photonic crystal fiber with Panda eyes structure. Using finite element analysis method, the transmission properties of Panda eyes photonic crystal fiber in terahertz wave regime was analyzed. The results show that terahertz photonic crystal waveguide with a low transmission loss can be designed if there are suitable parameters. When the transmission frequency f=0.5THz and d/Λ=0.8, the minimum transmission loss is less than 0.5dB/m.

In this paper, a laser cutting technology for the oil pipes with the thickness of 10mm, the diameter of 142mm and the material of N80 has been developed, in order to reduce the high hole-blast rate in processing. Experiments are taken on the Rofin DC025 slab CO₂ laser cutting system and a set of flexible fixtures. The reasons of forming blast-hole have been analyzed, and the influences of technique parameters on blast-hole rate have been studied, such as laser power, pulse frequency, laser delay, focus position and oxygen pressure. The results show that the blast-hole rate can be controlled lower than 5% at the conditions of laser power 1500W, laser delay 5s, pulse frequency 180Hz, the oxygen pressure 0.6 kg/cm², focus length 190mm, nozzle diameter 1.5mm.

This paper applied numerical simulation of temperature by using finite element analysis software Ansys to study a model of drilling on sticking plaster. The continuous CO₂ laser doing uniform linear motion and doing uniform circular motion irradiated sticking plaster to vaporize. The sticking plaster material was chosen as the thermal conductivity, the heat capacity and the density. For temperatures above 450 °C, sticking plaster would be vaporized. Based on the mathematical model of heat transfer, the process of drilling sticking plaster by laser beams could be simulated by Ansys. The simulation results showed the distribution of the temperature at the surface of the sticking plaster with the time of vaporizing at CO₂ laser to do uniform linear motion and to do uniform circular motion. The temperature of sticking plaster CO₂ laser to do uniform linear motion was higher than CO₂ laser to do uniform circular motion in the same condition.

The dielectric properties of near-stoichiometric LiNbO3:Fe and LiNbO3:Ce single crystals have been investigated by using a terahertz time domain spectroscopy (THz-TDS) in a frequency range of 0.4-1.8 THz at room temperature. When coupled with an applied external optical field, obvious photorefractive effects were observed, resulting in the modulation of the complex dielectric constant for the crystals, and reached up to 3%. However, the dielectric loss does not change appreciably. These findings were attributed to the change of spontaneous polarization in the crystals caused by the internal space charge field of photorefraction.

Based on the energy spectrum and maximum kinetic energy of accelerated ions, an analytical model was developed to calculate the magnetic foil trap mitigation efficiency of ion debris emitted from droplet-based laser-produced mass-limited plasmas for an application to extreme ultraviolet (EUV) lithography. The effects of magnetic field intensity, foil structures on the mitigation efficiency of different ionization state ions were investigated in order to establish the guideline for the optimum design of a mitigation system. The calculation results show that the foil trap mitigation efficiency η is calculated in the range of 92%~78% for a foil angle of 0.03 rad and foil length of 10 cm under magnetic field of B=0.1 T, which for the case of laser power densities and droplet target radius in the range suitable for extreme ultraviolet light source for lithography.

Electron-phonon coupling factor and electron heat capacity based on the electron density of states are investigated for transition metal Ni under femtosecond laser irradiation. The thermal excitation of d band electrons is found to result in large deviations from the commonly used approximations of linear temperature dependence of the electron heat capacity and the constant electron-phonon coupling factor. Results of the simulations performed with the two-temperature model demonstrate that the electron-phonon relaxation time becomes long for high fluence laser for Ni. The satisfactory agreement between our numerical results and experimental data of threshold fluence indicates that the electron temperature dependence of the thermophysical parameters accounting for the thermal excitation of d band electrons should not be neglected under the condition that electron temperature is higher than 10⁴ K.

This paper reports the scheme of terahertz (THz) wave generation on the basis of difference frequency generation in two-dimensional periodically structural Crystals pumped by CO₂ laser. The two orthogonal periodic structures individually compensate for both the phase mismatch of the launched lasers and the generated THz wave. Quasi phase matching (QPM) was designed to satisfy the wave vector phase matching condition in two-dimensional periodical GaAs crystals. The parallel to the direction of the pump wave propagation grating period Λ₁ and perpendicular to the direction of the pump wave propagation grating period Λ₂ of two-dimensional periodical GaAs crystals at the 100-1000μm (0.3-3THz) range are investigated. The length of the parallel to the direction of the pump wave propagation grating period is 90.17 μm and the length of the perpendicular to the direction of the pump wave propagation grating period is 83.69μm in the two-dimensional collinear QPM scheme to generate a frequency of 1 THz wave pumped by CO₂ laser. The result shown that the scheme of phase matching applies two-dimensional collinear quasi phase matching (QPM) is efficient to obtain high power conversion efficiency of THz wave.

A novel technique that is able to achieve high spatial resolution in the measurement of the spectral emission characteristics of laser produced expanding plasmas is reported. The image of expanding laser produced plasma is directly focused on the entrance slit of a stigmatic spectrometer coupled with image readout intensified charge-coupled device camera. The parallel spectra acquisition approach of this measurement has a better spatial resolution than conventional plasma emission spectroscopy measurements at different distances from the target. Based on the high spatial resolved measurements, the plasma plume UV-visible emission spectra in a vacuum of 10^-4 Pa by pulsed CO₂ laser ablating tin were obtained. Analysis of the spectra provides useful plasma parameters. Relative ion emission intensities provided electron temperature, and Stark broadened line widths yield electron densities. The high spatial resolution emission images give the plasma plume expansion dynamics. The understanding of the temporal and spatial distribution of laser produced plasma parameters of tin is of great interest to the control of the extreme ultraviolet emission process for lithography.

Propagation characteristics of flattened Gaussian beams through an annular apertured optical system remain unknown. Here we derive the approximate analytical expressions of flattened Gaussian beams passing through a paraxial optical system with an annular aperture based on the Collins integral and the expansion of the hard aperture function into a finite sum of complex Gaussian functions. Meanwhile, the corresponding closed-forms for the unapertured or circular apertured or circular black screen cases are also given. Some numerical examples are given to illustrate the propagation properties of flattened Gaussian beams through an optical system with an annular aperture. the numerical examples would be useful for some engineering applications.

We have fabricated high quality THz tunable bandpass filters based on one dimensional photonic crystal cavity. The filter have a high quality about 1500 and can have a very narrow passband and the full width at half maximum (FWHM) can be about 200MHz and the peak transmission is higher than -4dB. With the length of cavity adjusted by a motorized linear stage, the central frequency of the filter can be tuned continuously. The bandwidth and insertion loss is also analyzed theoretically.

The competition on population inversion between two lasing modes in one-dimensional (1D) active random media is investigated by simultaneously solving Maxwell's equations and rate equations of electronic population. Results indicated that the increasing of concentration of the dye increase the spectral intensity of the dimer and the increase of the pump energy produces a major radiative and non-radiative energy transfers from monomers to dimers. The simulations of the new monomerdimer laser model agree very well with the experimental datas and promote the development of random lasing in the mixed dye media.

Electrically controlled wavelength switchable terahertz band pass filter based on photonic crystal structures with LC defect layer is proposed and discussed. The wavelength switching can be realized by reorienting liquid crystal molecules through adjusting the applied electric field. Numerical analyses results have shown that the proposed structure has the potential to realize electrically controlled terahertz filter with a high narrow transmission band and very sharp edges. What s more, the device can also function as a terahertz switch, and the theoretical extinction ratio of the device can reach more than 50dB.

The theory of laser-induced plasmas addition to hypersonic airflow off a vehicle to increase air mass capture and improve the performance of hypersonic inlets at Mach numbers below the design value is explored. For hypersonic vehicles, when flying at mach numbers lower than the design one, we can increase the mass capture ratio of inlet through laser-induced plasmas injection to the hypersonic flow upstream of cowl lip to form a virtual cowl. Based on the theory, the model of interaction between laser-induced plasmas and hypersonic flow was established. The influence on the effect of increasing mass capture ratio was studied at different positions of laser-induced plasmas region for the external compression hypersonic inlet at Mach 5 while the design value is 6, the power of plasmas was in the range of 1-8mJ. The main results are as follows: 1. the best location of the plasma addition region is near the intersection of the nose shock of the vehicle with the continuation of the cowl line, and slightly below that line. In that case, the shock generated by the heating is close to the shock that is a reflection of the vehicle nose shock off the imaginary solid surface-extension of the cowl. 2. Plasma addition does increase mass capture, and the effect becomes stronger as more energy is added, the peak value appeared when the power of plasma was about 4mJ, when the plasma energy continues to get stronger, the mass capture will decline slowly.

Absorption spectra in the terahertz region between 6 and 66 cm^-1 (0.2 ~ 2.0 THz) were measured for S-(+)-, R-(-) and RS-naproxen pharmaceutical molecules in crystalline form using time-domain terahertz spectroscopic (THz-TDS) technique at room temperature. Different absorption features were observed for the racemic RS-naproxen and its corresponding enantiomers (S-(+)- and R-(-)-naproxen). The observed THz absorption bands are strikingly sensitive to the change of subtle conformational structures despite that the isostructurality exists within such crystal molecules. The results show that the THz-TDS technique can be definitely used for distinguishing between chiral and racemic compounds in pharmaceutical and biological fields.

Far-infrared vibrational absorption of a series of dihydroxybenzoic acid (DHBA) compounds with different substituted hydroxy group at different positions have been investigated using terahertz time-domain spectroscopy (THz-TDS) at room temperature. The experimental results show large difference among absorption spectra of different DHBA (2,3-DHBA, 2,4-DHBA, 2,5-DHBA, 2,6-DHBA) compounds in 0.2 ~ 2.0 THz region, which probably originated from the difference of intra-molecular and inter-molecular hydrogen bonds due to the presence of two hydroxyl group in different positions with respect to the carboxylic group in different DHBAs. All the experimental DHBAs vibrational modes showed distinct fingerprint absorption in THz region and theorectical calculation based on density functional theory (DFT) was carried out to assist the analysis and assignment of the vibrational modes. The results indicate that THz-TDS technology can not only give a new experimental method to identify and characterize the position isomerism effect of hydroxyl group between such different kinds of DHBAs from molecule-level, but also provide a useful suggestion for further assessing the possible relationships between the DHBAs vibrational properties and the effects of the substituted hydroxy group position to better know their biochemical activities in food, pharmaceutical and cosmetic fields.

We have studied the absorption spectral of L-and DL-fudosteine using terahertz time-domain spectroscopy (THz-TDS) at room temperature. The results show that both of them have unique absorption fingerprint peaks in terahertz range and can be identified by these peaks. The absorption spectrum of the fudosteine capsule has also been studied. Its absorption spectrum is similar to that of L-fudosteine. Thus, it proves that the main component of fudosteine capsule is L-fudosteine. The study indicates that THz-TDS technology is a new method to identify and analyze main components of material.

The wave structures of type IV shock interaction will be changed when injected laser energy, and it can decelerate the type IV shock interaction thermal ablating effect on the blunt body by laser energy injection. A high resolution numerical method based on finite volume method and domain decomposition of structural grid is used to compute the influence of laser single pluse energy and laser continuous energy injected into type IV shock interaction at Mach number 3.45.The result shows that the pressure and temperature on the blunt body surface will be increase slightly when injected laser energy with single pluse in a relatively short period(50μs to 60μs ),then it will be decreased quickly, and it will be restored to the original state at last. The pressure and temperature on the blunt body surface will be increased slightly when injection a little laser energy with continuous and decreased with the increase of the injected laser energy, but the temperature on the blunt body surface will be increased quickly when the injection laser energy over 160kW.

We proposed a sensitive gas sensor based on one dimensional photonic crystal (1D-PC) cavity in terahertz frequency range. The cavity Consists of stacks of high-resistivity silicon layers and air spacers, and has a very high quality factor exceeding 1200. The defect modes are very sensitive to the small change of the refractive index of materials in the cavity. The resonant mode shifts about 34MHz when the air in cavity is replace by CO2. Such shift of frequency is attributed to the refractive index change of air in the cavity. The frequency shifts for different ratio mixture of air and CO2 are also measured. Thus, the cavity can be used to measure components ratio of mixed gas.

The paper describes a new THz wave detector. The bi-material of niobium nitride and aluminum, which has a large difference in thermal expansion coefficient, is used to fabricate the micro-cantilever arrays of substrate-free using MEMS technology. The niobium nitride is used to absorb THz, and aluminum is used as the deformation material. The method of software simulation is used to research the optimum thickness ratio of the bi-material for the best design of the micro-cantilever. In addition, in order to prevent the heat diffusion, the micro-cantilever arrays is placed in a vacuum chamber which has the function of vibration prevention using the mechanical pump and molecular pump to keep the high vacuum degree for improving the signal to noise ratio of the detection system. The reflection type visible light optical readout system is used to acquire the THz wave information indirectly. Furthermore, the method of difference processing is used to process image for improving systemic resolution. At last, a THz source with a power of 5mW and a frequency of 973GHz is used for detection experiment, and the data processing results show that the micro-cantilever has deformed.

Laser forming is a technique consisting in the design and the construction of complex metallic work-pieces with special shapes, difficult to achieve with the conventional techniques. By using lasers, the main advantage of the process is that it is contactless and does not require any external force. It offers also more flexibility for a lower price. This kind of processing interests the industries that use the stamping or other costly ways for prototypes such as in the aero-spatial, automotive, naval and microelectronics industries. The analytical modeling of laser forming process is often complex or impossible to achieve, since the dimensions and the mechanical properties change with the time and in the space. Therefore, the numerical approach is more suitable for laser forming modeling. Our numerical study is divided into two models, the first one is a purely thermal treatment which allows the determination of the temperature field produced by a laser pass, and the second one consists in the thermomechanical coupling treatment. The temperature field resulting from the first stage is used to calculate the stress field, the deformations and the bending angle of the plate. The thermo-mechanical properties of material are isotropic, but temperature-dependant.

In laser cutting process, an assisting gas is used to improve the mass removal rate from the cutting kerf and protect the kerf surfaces from the high temperature exothermic reactions, such as oxidation reactions, during the cutting process. Numerical simulations are carried out using a commercial CFD code Fluent. In the first part of this work, the behavior of assisting gas flow is computed without heat transfer in laminar model which reveals a vortex structures in the flow at the inlet and exit of the kerf, which may directly affect the surface quality in real gas-laser cutting of metals. The largest vortex, which arises at the channel exit, collects and accumulates the liquid flowing down the channel walls. The study with increasing the angle of the kerf shows that the vortices disappear, and a stable vortex-free attached gas flow is formed. In other side, the heat transfer from the kerf wall to the flow of the assisting gas is important for quality cutting which is carried out in second part of this study including the RNG/κ-ε model. The kerf wall temperature is kept at 1500K to resemble the laser cutting process. The distance between the nozzle exit and the kerf top surface to nozzle diameter is selected as H=0.7, where H is the stand-off-distance.

The spectral characteristics of selected molecular sieves (3A, 4A, 5A, 13X and synthetic zeolite) in a terahertz (THz) range were studied by THz time-domain spectroscopy technologies (THz-TDS). The chemical composition of a molecular sieve is M_x/n[(AlO₂)x·(SiO₂)y]·zH₂O, where M is metal cation and n is the valence of the metal cation. The absorption coefficients and refractive indices were extracted in the spectra. Different from that of the A-type molecular sieves, the absorption curves and refractive indices of synthetic zeolite and 13X molecular sieve display large fluctuation as the frequency change. In addition, two kinds of related compounds (Al₂O₃ and quartz sand) were studied by using THz-TDS. The Al₂O₃ shows weak absorption and quartz sand has three typical absorption peaks at 0.89, 1.3, 1.55 THz. The refractive index of Al₂O₃ is kept at about 1.27 while that of quartz sand show large fluctuations. The present results suggested that the THz spectra of molecular sieves are in dependent of their types and indicated the potential of THz technology for the molecular sieve industry.

Photoconductive antennas with different structures generate terahertz (THz) waves with different peak frequencies at the same experimental conditions, so does the same antenna at different experimental conditions. It is necessary to investigate the determinants of peak frequencies of THz radiation from photoconductive antenna to obtain the THz wave with required peak frequency. In this paper, the factors of laser spot size, trapping time, carrier lifetime, carrier density, bias field, antenna gap size were analyzed based on our experiment and literatures. The peak frequency moved to higher frequency with the decrease of antenna gap size, carrier lifetimes, trapping time, laser beam diameter, and the peak frequency moved to lower frequency with the decrease of bias field, carrier densities.

The terahertz transmission spectra of three different persistent organic pollutants (POPs) (aldrin, dieldrin, and endrin) are measured by using terahertz time-domain spectroscopy (THz-TDS) in the terahertz region of 0.2-1.8THz. The spectral dependence of the absorption for individual three kinds of POPs is extracted from the transmission data. Computational chemistry using the B3LYP density functional method is used to study structure and internal rotations in POPs, where results strongly suggest that frequencies of the POPs internal rotor correspond to the observed spectra. The absorption coefficient for the soil/aldrin mixture is 19.64cm^-1 at 1.41THz, 20.91cm^-1 at 1.57THz, 13.69cm^-1 at 1.78THz. For soil/dieldrin mixture, the frequency positions of prominent absorption features at 1.29, 1.4 and 1.56THz are observed. The absorption coefficient for the soil/dieldrin mixture is 16.73cm-1 at 1.29THz, 18.85cm^-1 at 1.4THz, 24.5cm^-1 at 1.56THz. There exhibits three strong absorption peaks coefficient of the soil/endrin mixture at the frequency of 1.58THz and 1.67THz. The absorption coefficient of the soil/endrin mixture is 6.24cm^-1 at 1.58THz, 12.58cm^-1 at 1.67THz. There is reasonably good agreement between theory and experiment. The results show that the THz-TDS can be used to study POPs in soil quality evaluation or safety inspection further.

Silver-modified ZnO nanorods film has been prepared through a novel approach. ZnO nanorods film was fabricated via a wet chemical route and a self-assemble method was taken to fabricate silver nanoparticles on the ZnO nanorods. The products were characterized by field emission scanning electron microscope and X-ray diffraction. The formation mechanism of the Ag/ZnO nanorods film was also discussed. The study result would be a huge contribution to the terahertz research.

We numerically investigate mid-infrared supercontinuum generation in single mode fluoride fiber pumped by 1.56μm femtosecond fiber lasers. To get high energy conversion efficiency in mid-infrared region, the ratio of power generated in 2.5 ~ 5 μm range to the total input power for supercontinuum generation is optimized by varying the pulse width, peak power and fiber length. The long wavelength edge of the supercontinuum spectrum can be extended to 5μm in a 9 cm long fluoride fiber pumped by a 1.56μm fiber laser with a pulse width of 200 fs and a peak power of 2 MW, and the corresponding ratio of power generated in 2.5 ~ 5 μm range to the total input power is about 29.6%. The spectral broadening is mainly caused by self-phase modulation, stimulated Raman scattering and four-wave mixing. The simulated results show that high energy conversion power supercontinuum light source in 2.5 ~ 5 μm range could be obtained in fluoride fibers pumped by 1.56μm femtosecond fiber lasers.

We reported a technology of gray-scale imaging using broadband terahertz pulse. Utilizing the spatial distribution of different frequency content, image information can be acquired from the terahertz frequency domain analysis. Unlike CCDs(charge-coupled devices) or spot scanning technology are used in conversional method, a single-pixels detector with single measurement can meet the demand of our scheme. And high SNR terahertz imaging with fast velocity is believed.