This PDF file contains the front matter associated with SPIE Proceedings Volume 9275, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

Terahertz spectroscopy is sensitive to probe several aspects of biological systems. We have reported the terahertz dielectric spectrum is able to identify the type of the charges in the hydrogen-bonded antibodies’ networks in our previous work. Recently we demonstrate a highly sensitive THz-TDS method to monitor binding interaction of influenza hemagglutinin (HA) against its target antibody F10. The terahertz dielectric properties of HA was strongly affected by the presence of a specific antibody. Protein solution concentration or even molecular binding interaction can also affect the terahertz signal. This enables us to detect the specificity and sensitivity of antibody-antigen binding under THz radiation.

In this work, we present a terahertz (THz) isolator in metal parallel plate waveguide (PPWG). A magneto-optical film with 30μm thickness is coated on one side of the metal plate of PPWG with 100μm width, forming a metal- magnetoair- metal hybrid waveguide. Due to the non-reciprocity of magneto-optical medium and the asymmetry of the waveguide structure, this waveguide show a strong one-way transmission property. The numerical simulation shows that this THz isolator has a maximum isolation of 30dB and a 20dB operating bandwidth of 90GHz under a magnetic field of 0.3T, and its insertion loss is smaller than 0.5dB. Moreover, this operating frequency band can be widely tuned by changing the external magnetic field and temperature. This low-loss, high isolation, broadband tunable nonreciprocal THz waveguide has a great potential for THz application systems.

Metallic helices have been extensively researched and demonstrated for their application as broadband circular polarizers in different frequency regimes. For making such 3D helices, two photon lithography (TPL) has been employed in conjunction with electroplating of metals. Recently, our group has demonstrated selective silver electroless plating of two photon fabricated polymer (SU-8) structures on silicon substrate. This procedure allows us to make metal-coated polymer helices. In this work, we examine how these fabrication process parameters could be tailored to obtain higher extinction ratios for circular polarizers in THz regime (or MIR regime). We further analyze the role of aspect-ratio of helices in their polarizing action. We will present both simulation and experimental results to show the improved performance of the polarizers.

We present and demonstrate a new type of single resonator based planar metamaterial exhibiting electromagnetically induced transparency (EIT)-like transmission behavior. The novel design involves physically coupled split-ring resonator (SRR) and a dipolar ring as opposed to many inductively coupled resonators explored in the past. Both experiments and simulations reveal a dispersive transparency due to coupled resonances and the underlying mechanism. Further, the conductive and inductive coupling scenarios for this structure were compared where conductive coupling was found to coerce the direction of light induced currents and stronger in effect than inductive coupling. Resonance tuning is achieved by moving the bar coupling SRR and the ring. Hence, we show that conductive coupling has potential in tailoring coupled resonances of desired quality factor and fabricating metamaterials for enhanced sensing.

A critical electromagnetic response of a self-complementary structure was investigated. The nearly perfect selfcomplementary checkerboard patterns were fabricated by the electron-beam lithography and their electromagnetic responses are measured in the terahertz region. The electromagnetic responses are affected drastically by the small structural difference even though the differences are less than 0.1% of the wavelength of the incident electromagnetic waves. The sample most close to the self-complementary checkerboard pattern shows a less frequency dependent response, which is expected for the self-complementary structures. In this sample, the metallic squares seem to be connected randomly from the SEM observation. The effect of the structural randomness in metal mesh structures is also investigated to obtain the common electromagnetic properties in randomly connected systems.

We present a terahertz gas sensor based on a simple one-dimensional photonic crystal cavity. Although the manufacture process is quite easy, this cavity exhibits quite high quality factors for assisting the realization of very high sensitivity in the gas refractive index sensing. Transmission measurements of the one dimensional photonic crystal cavity under different gaseous environments showed that the resonant frequency depends linearly on the refractive index of the ambient gas. In our experiment, a change of the refractive index by 1.4×10^-5 leads to a shift of the resonant frequency by 4 MHz, which corresponds to 6% of the change of hydrogen concentration in air. By using the former reported quality factor of ~1.1×10⁴, a refractive index change as small as 7×10^-6 can be expected.

Understanding the low-frequency normal modes of amino acids, the building blocks of proteins, is crucial to reveal the vibration-function relationship in the macromolecular system. Recent advances in terahertz spectroscopy (THz) and solid-state density functional theory (DFT) have ensured an accurate description of low-frequency modes of amino acids. New knowledge people have learnt so far is that the inter- and intra-molecular vibrations are strongly mixed with each other in the THz region through the vibrational coordinate mixing. Rich information is believed embedded in this phenomenon. We introduce a generalized mode-analysis method that allows for the accurate decomposition of a normal mode of interest into the three intermolecular translations, three principal librations and various intrinsic intramolecular vibrations. This mode-analysis method will be demonstrated in the crystalline C₆₀ systems and then applied to shed light on the nature of low-frequency phonons of glycine, diglycine and triglycine. This method helps reveal new intramolecular vibrational modes on the first hand, and more importantly, illuminate a new phenomenon of the frequency distribution of intramolecular vibrations (FDIV). FDIV describes the possible broad distributions of important intramolecular vibrations in the low-frequency normal modes. The FDIV concept may indicate an additional mechanism for the intramolecular vibrations to become thermally active and participate in various biological functions.

We investigated the broadband terahertz (THz) emission from sub millimeter laser-induced plasmas. The angular dependent emission from the source was characterized with coherent detection, showing that the radiation pattern peak is located 80 degrees away the propagation direction of the excitation laser. Our findings support the laser ponderomotive force as the main driver for the generation of THz transients. We report the measurement of THz waveforms generated in ambient air with laser excitation energies as low as 660 nJ. The experimental results suggest the laser-induced microplasma as a promising approach to reduce the laser threshold typical of THz air photonics systems of many orders of magnitude, with the result of scaling down the cost of broadband terahertz spectroscopy.

In this paper we present an innovative data and image processing sequence to perform non-destructive inspection from 3D terahertz (THz) images. We develop all the steps starting from a 3D tomographic reconstruction of a sample from its radiographs acquired with a monochromatic millimetre wave imaging system. Thus an automated segmentation provides the different volumes of interest (VOI) composing the sample. Then a 3D visualization and dimensional measurements are performed on these VOI, separately, in order to provide an accurate nondestructive testing (NDT) of the studied sample. This sequence is implemented onto an unique software and validated through the analysis of different objects

We fabricated a terahertz anti-reflective structure on a polystylene by using a hot-embossing method. Polystylene was spin-coated onto a silicon substrate and then transformed by using a metallic mould comprising a bunch of Chinese acupuncture needles. The transformation layer yielded gradient refractive index profiles on the substrate which can reduce the surface reflection effectively. The samples were evaluated by a terahertz time-domain spectroscope. Compared with a bare silicon substrate, we observed an increase of ~30% in the transmittance. We also observed broader bandwidth properties compared with a single-layer antireflective structure. The process imposes no substrate limiting; i.e., it has great potential to be applied onto various THz devices.

In this paper, we have investigated the polarization dependence of terahertz wave through the metallic meanderline structure on the different thicknesses of polyimide substrate. The meanderline wave plates are designed by using software of CST Microwave Studio. The 200 nm thickness of gold film is used as metallic layer deposited on the polyimide substrate with different thicknesses. The ellipticity η is obtained by the simulating transmission and phase, η=0 corresponds to linearly polarized transmission, while η=1 and -1 corresponds to left-handed and right-handed circular polarization. The intermediate value of η indicates the elliptically polarization. The simulation results show that the absolute value of ellipticity reach the maximum of 0.999 at 0.505THz, 0.479THz and 0.391THz when the substrate thickness t=10μm, 30μm and 60μm, respectively. In addition, the metallic microstructure of meanderline displays a large bandwidth of THz operation. The ellipticity is over 99% in the THz band of 457 GHz to 532 GHz, 426 GHz to 508 GHz, 356 GHz to 486 GHz corresponding to the above three kind of substrate thicknesses. The bandwidth increases and shows red shift with increasing of substrate thickness. These results provide a reference for the design and manufacture of THz polarization conversion device.

The high-speed and high dynamic range readout circuits can realize a good performance that achieving intra-scene wide dynamic range，and the readout circuits could get more details of a target view that include very dark and very bright signal. A new architecture of readout circuits with high speed and high dynamic range is introduced. In order to achieve high dynamic range, we use a special architecture of readout circuits. The circuits allow the very high signal to input, and output the signal without damaging. The input stage use a CTIA architecture in the circuits, and connect a feedback circuit and a S/H circuit in the output of CTIA. The architecture of the feedback is a circuit to control the reset switch of CTIA, when a strong signal inputing, the feedback circuit judge the signal of output, if the signal over the reference signal that have been set, the feedback circuit output a reset signal, the output of CTIA is reset to the initial state. A counter records the reset signal, and get the total times of reset. At the last stage of integration period，the S/H circuit samples the signal and a integration period is over. As the circuits could realize multiple reset, the signal would never reach saturation state, and it can achieve a very high range in the output. We use the GLOBALFOUNDRIES 0.35μm technology and simulate the designed circuits with Cadence IC, and test the functions, then analyze the performance of the circuits from the results.

A 128×128 matrix readout integrated circuit (ROIC) for 15×15 μm² InGaAs focal plane array (FPA) is reported in this paper. Capacitive-feedback Trans-Impedance Amplifier (CTIA) and correlated double sampling (CDS) are both involved in ROIC pixel which dissipates 90nW and has a full-well-capacity (FWC) of about 78,000 e-. Noises of ROIC pixel are analyzed and distribution method of capacitors in pixel is discussed in order to obtain low-noise performance. In column buffer circuit, a new pre-charging technique is developed to realize readout rate of 20 MHz with low power consumption. The ROIC is fabricated with 0.18-μm 3.3 V mixed signal CMOS process. Test results show that the ROIC has an equivalent input noise of about 181e- and can achieve a readout rate of 20 MHz.

In order to segment the target well and suppress background noises effectively, an infrared image segmentation method based on spatial coherence histogram and maximum entropy is proposed. First, spatial coherence histogram is presented by weighting the importance of the different position of these pixels with the same gray-level, which is obtained by computing their local density. Then, after enhancing the image by spatial coherence histogram, 1D maximum entropy method is used to segment the image. The novel method can not only get better segmentation results, but also have a faster computation time than traditional 2D histogram-based segmentation methods.

Since the technology trend of the third generation IRFPA towards resolution enhancing has steadily progressed,the pixel pitch of IRFPA has been greatly reduced.A 640×512 readout integrated circuit(ROIC) of IRFPA with 15μm pixel pitch is presented in this paper.The 15μm pixel pitch ROIC design will face many challenges.As we all known,the integrating capacitor is a key performance parameter when considering pixel area,charge capacity and dynamic range,so we adopt the effective method of 2 by 2 pixels sharing an integrating capacitor to solve this problem.The input unit cell architecture will contain two paralleled sample and hold parts,which not only allow the FPA to be operated in full frame snapshot mode but also save relatively unit circuit area.Different applications need more matching input unit circuits. Because the dimension of 2×2 pixels is 30μm×30μm, an input stage based on direct injection (DI) which has medium injection ratio and small layout area is proved to be suitable for middle wave (MW) while BDI with three-transistor cascode amplifier for long wave(LW). By adopting the 0.35μm 2P4M mixed signal process, the circuit architecture can make the effective charge capacity of 7.8Me^- per pixel with 2.2V output range for MW and 7.3 Me^- per pixel with 2.6V output range for LW. According to the simulation results, this circuit works well under 5V power supply and achieves less than 0.1% nonlinearity.

Recent years, infrared guidance technology has more and more applications in the field of precise guidance, because it is not limited by the night or the meteorology.The development of infrared guidance technology depends on the infrared image processing technology.This paper introduces an algorithm for infrared image nonuniformity correction based in FPGA. It uses multiplication instead of division and adopts efficient pipeline technology to reduce the system logic resource usage and improve efficiency of the system.Because infrared imaging is influenced by environmental temperature, this pape proposes an infrared nonuniformity correction algorithm with the compensation if environment temperature. This algorithm is very effective to reduce the influence of the environment temperature on infrared imaging. This infrared image processing system for infrared imaging laid a foundation for the application of the infrared guidance in the field of precise guidance.

In this paper, we report on the measured and simulated far-field beam-patterns of a quasi-optical NbN superconducting hot electron bolometer (HEB) mixer at 600GHz. This superconducting HEB mixer consists of an extended hemispherical lens with a diameter of 12.7mm and an extension length of 2.45mm, a twin-slot planar antenna (two slots measuring 148.5μm × 10.4μm with a separation of 78.98μm) and a 5.5-nm thick NbN thin-film micro-bridge with an area of 2μm × 0.2μm . The far-field beam pattern of this mixer is measured by a direct-detection technique with a dynamic range of nearly 25dB, showing an FWHM beam angle of 2.7° and -18dB level of the first side-lobe. The measured beam of the quasi-optical mixer is nearly collimated and has good Gaussian beam efficiency. In addition, the far-field beam-pattern is measured at different DC bias voltages of the superconducting HEB mixer and at different bath temperatures. The measured results are compared with the ones simulated by two different methods. Detailed measurement and simulation results will be presented.

Terahertz imaging can make up the defect of imaging opaque samples in visible light domain. Digital holography is a new technology for extracting full information of the original object. In the paper, the improved angular spectrum (AS) algorithm is coulping the original AS algorithm with direct current (DC) suppression method, apodization and piecewise-nonlinear transformation. The reconstruction characteristics of the algorithm have been studied by numerical analysis and experimental researches. The experimental results validate the application value of the algorithms in improving 2D reconstructed image quality in terahertz Gabor inline digital holography.

A simulated annealing method for material parameter extraction with terahertz time-domain spectroscopy is introduced to improve the common extraction method. The simulated annealing method seeks the global minimum of the error function to obtain material constants where the characterized material is not constrained by a certain boundary condition. It is shown from the research results that more accurate material parameters can be acquired to meet the actual requirements of material analysis by use of the simulated annealing method.

A 100GHz Schottky diode mixer based on quartz substrate is presented, which will be used as the detector for the millimeter imaging. The Schottky diode is modeled based on its physical dimension thus its high frequency parasitic parameters can be fully taken into consideration. The measured conversion loss is better than 10dBm over 95~105GHz with 8dBm LO pump at 49.53GHz. The measured result is also in excellent accord with the simulated model.

In this paper, we report on the spectrum measurement of a terahertz (THz) pulse signal using a Fourier transform spectroscopy (FTS) system. The THz pulse signal is a quantum cascade laser (QCL) at 3.7THz with changeable repeating frequency and duty cycle. With a fixed duty cycle, the repeating frequency is changed to investigate the maximum value that can be measured with an FTS system. The relationship between the spectrum intensity and the pulse width is investigated through the variance of the duty cycle with a given repeating frequency. Detailed experimental results will be presented.

We presented a passive THz opto-mechnical scanning imaging method using a single detector and a trihedral scanning mirror. The system improved the imaging speed through employing two flapping mirrors. Also the trihedral scanning mirror and an ellipsoidal mirror were adopted. The parameters were set as follows: the best imaging distance was 2.2m with the image range of 1.6m（W）×1.6m（H）, the imaging time was 2s, and the resolution was 3cm. We imaged human body with different objects concealed under their clothes, such as buckle, ceramic chip, etc.

In this paper, a high performance readout integrated circuit (ROIC) designed for long wave infrared (LWIR) detectors is introduced, which has high dynamic range (HDR). To accommodate the wide scene dynamic range requirement, special circuit architecture is used to the input unit cell. A capacitive feedback transimpedance amplifier (CTIA) as input circuit is used to provide high injection efficiency, low input resistance, good linearity, precise voltage bias. Because of the restriction of the layout area, four unit cells will share an integration capacitor and each unit cell has a correlated double sampling (CDS) circuit, which allows the infrared focal plane arrays (IRFPA) to be operated in full frame snapshot mode and provides the maximum integration time available. The charge transfer circuit is used and we don't need to consider the drive ability of the unit cell. The simulation results confirm that the ROIC provides over a factor of 70dB dynamic range with the 5.0v power supply.

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.

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.

Terahertz time-domain spectroscopy is used to research the intermolecular or intramolecular interactions and some optical properties, such as refractive index, dielectric constant and absorption coefficient. As the dopant in terahertz band, non-absorbing particles, such as polyethylene or others, are usually mixed with pure biological samples by compressing tablets. Due to inhomogeneity and different particle sizes in the tablets, the unobvious absorption from pure sample was affected by doped particle in mixtures. In order to extract the permittivity of pure sample from mixture, Bruggeman effective medium approximation (EMA) theory can be applied. The optical constants and the permittivity of the pure sample can be obtained by using EMA from a composite medium of biological sample and polyethylene. EMA is employed in this work and the relationships between the calculation results and particle sizes are to be explored. It shows that the practicability of Bruggeman effective medium theory in the identification of terahertz spectrum of mixture.

We demonstrate that the transmission properties of terahertz metamaterials based on split-ring resonators (SRR) is significantly dependent upon the incident wave polarization. Structures with different rotation symmetry are patterned on intrinsic gallium arsenide (GaAs), and examined in our work with finite element method. The EM responses of proposed structures under different polarization incidence THz wave are simulated. The simulation results demonstrate that the polarization-sensitive characteristic is determined by the rotation symmetry of the SRR - metamaterials units. Our work can be a guide for the design of novel metamaterials modulator and other polarimetric THz devices.

In order to acquire high-resolution molecular absorption spectrum, a measurement system consisting of two Erbium-doped fiber optical frequency combs based on multi-heterodyne detection method is established. Preliminary result shows that the specific line in the RF spectrum corresponding to 6452.59 cm^-1 in the optical region, where there is an error of 0.14 cm^-1 compared with the simulation result. And the further improvement of this system will be discussed in the end.

The increasingly emerging terrorism attacks and violence crimes around the world have posed severe threats to public security, so carrying out relevant research on advanced experimental methods of personnel concealed contraband detection is crucial and meaningful. All of the advantages of imaging covertly, avoidance of interference with other systems, intrinsic property of being safe to persons under screening , and the superior ability of imaging through natural or manmade obscurants, have significantly combined to enable millimeter-wave (MMW) radiometric imaging to offer great potential in personnel concealed contraband detection. Based upon the current research status of MMW radiometric imaging and urgent demands of personnel security screening, this paper mainly focuses on the experimental methods of indoor MMW radiometric imaging. The reverse radiation noise resulting from super-heterodyne receivers seriously affects the image experiments carried out at short range, so both the generation mechanism and reducing methods of this noise are investigated. Then, the benefit of sky illumination no longer exists for the indoor radiometric imaging, and this leads to the decrease in radiometric temperature contrast between target and background. In order to enhance the radiometric temperature contrast for improving indoor imaging performance, the noise illumination technique is adopted in the indoor imaging scenario. In addition, the speed and accuracy of concealed contraband detection from acquired MMW radiometric images are usually restricted to the deficiencies in traditional artificial interpretation by security inspectors, thus an automatic recognition and location algorithm by integrating improved Fuzzy C-means clustering with moment invariants is put forward. A series of original results are also presented to demonstrate the significance and validity of these methods.

A complex filtering method for eliminating systematic and random noises of THz-TDS is proposed. This method is the combination of deconvolution and wavelet filtering algorithms. A self-reference method for extracting the complex refractive index of material accurately is also proposed in order to avoid a phase shift due to the misplacement between the surfaces of the reference and sample using the time-domain terahertz reflection spectroscopy. The basic idea of self-reference method is that the first and the second peaks of the reflection spectrum of solid pellets are regarded as the reference and sample signals, respectively. Thus more information of samples can be extracted because of a longer optical path, and meanwhile, phase error can be avoided by obtaining the reference and sample signals through a single measurement. According to the Fresnel formulas, we deduce the expression of complex refractive index and then design an iterative algorithm for solving it. We choose the glucose solid pellets as samples to test the self-reference method. After measuring the time-domain reflection spectrum, we adopted the complex filter method for filtering and utilized the self-reference method to extract the complex refractive index. Based on Density Functional Theory (DFT), the characteristic absorption spectrum of multiple glucose molecules in the THz absorption spectroscopy was obtained by the simulation analysis on the vibration of multiple glucose molecules. The results indicate that the absorption peaks appear in the absorption coefficient curves at the corresponding frequency positions which are approximately consistent with the results of the simulation based on DFT. So the methods we proposed can help improve the retrieval accuracy of complex refractive index.

Terahertz time-domain spectroscopy (THz-TDS) is a detection method of biological molecules with label-free, non-ionizing, non-intrusive, no pollution and real-time monitoring. But owing to the strong THz absorption by water, it is mainly used in the solid state detection of biological molecules. In this paper, we present a microfluidic chip technique for detecting biological liquid samples using the transmission type of THz-TDS system. The microfluidic channel of the microfluidic chip is fabricated in the quartz glass using Micro-Electro-Mechanical System (MEMS) technology and sealed with polydimethylsiloxane (PDMS) diaphragm. The length, width and depth of the microfluidic channel are 25mm, 100μm and 50μm, respectively. The diameter of THz detection zone in the microfluidic channel is 4mm. The thicknesses of quartz glass and PDMS diaphragm are 1mm and 250μm, individually. Another one of the same quartz glass is used to bond with the PDMS for the rigidity and air tightness of the microfluidic chip. In order to realize the automation of sampling and improve the control precise of fluid, a micropump, which comprises PDMS diaphragm, pump chamber, diffuser and nozzle and flat vibration motor, is integrated on the microfluidic chip. The diffuser and nozzle are fabricated on both sides of the pump chamber, which is covered with PDMS diaphragm. The flat vibration motor is stuck on the PDMS diaphragm as the actuator. We study the terahertz absorption spectroscopy characteristics of glycerol with the concentration of 98% in the microfluidic chip by the aid of the THz-TDS system, and the feasibility of the microfluidic chip for the detection of liquid samples is proved.

THz radiation can penetrate through many nonpolar dielectric materials and can be used for nondestructive/noninvasive sensing and imaging of targets under nonpolar, nonmetallic covers or containers. Thus using THz systems to "see through" concealing barriers (i.e. packaging, corrugated cardboard, clothing) has been proposed as a new security screening method. Objects that can be detected by THz include concealed weapons, explosives, and chemical agents under clothing. Passive THz imaging system can detect THz wave from human body without transmit any electromagnetic wave, and the suspicious objects will become visible because the THz wave is blocked by this items. We can find out whether or not someone is carrying dangerous objects through this image. In this paper, the THz image enhancement, segmentation and contour extraction algorithms were studied to achieve effective target image detection. First, the terahertz images are enhanced and their grayscales are stretched. Then we apply global threshold segmentation to extract the target, and finally the targets are marked on the image. Experimental results showed that the algorithm proposed in this paper can extract and mark targets effectively, so that people can identify suspicious objects under clothing quickly. The algorithm can significantly improve the usefulness of the terahertz security apparatus.

A terahertz microfluidic chip which was fabricated out of quartz and polydimethylsiloxane (PDMS) was designed. The quartz acted as a substrate, on which a microfluidic channel with a height of 50 micrometer was etched by lithography technology. PDMS is a kind of easy fabricated and cheap polymer to cover the quartz substrate. It’s widely used in microfluidic applications for its numerous characteristics such as good insulation, colorlessness and transparency, high-voltage endurance and excellent optical quality. The transmittance of the chip was measured first. Increasing the frequency from 0.2 THz to 1.4 THz decreases the transmittance of microfluidic chip rapidly, where reaches as high as 80% when the frequency is 0.2 THz. The chip shows a high transmittance of above 40% from the range from 0.2 THz to 0.8 THz. Then THz spectra of glycerol, water and their mixture in the microfluidic chip were measured, respectively. Not only the time domain spectra but frequency-dependent amplitude spectra present significant differences of different kinds of liquids and different concentrations of the same glycerol. The absorption spectra result shows a monotonic increase in the absorption coefficient of the glycerol, water and the mixture with increasing frequency, respectively. It matches the fact that different molecules or the same molecules of different concentrations present different absorption coefficients in the terahertz band. All of the above indicate that this microfluidic chip is available in measurement of the samples in liquid and it’s able to realize real-time and label-free measurement for biochemistry samples in terahertz time-domain-spectroscopy(THz-TDS). Since the depth of the micro-channel is 50 μm，the detectable liquid in the chip only has an value of less than 10 μL, microfluidic chips offer a new platform for performing THz spectroscopy of small quantities of biomolecules using low-power THz sources.

Terrorist attacks make the public safety issue becoming the focus of national attention. Passive terahertz security instrument can help overcomesome shortcomings with current security instruments. Terahertz wave has a strong penetrating power which can pass through clothes without harming human bodies and detected objects. However, in the lab experiments, we found that original terahertz imagesobtained by passive terahertz technique were often too vague to detect the objects of interest. Prior studies suggest that learning-based image super-resolution reconstruction(SRR) method can solve this problem. To our knowledge, we applied the learning-based image SRR method for the first time in single-frame passive terahertz image processing. Experimental results showed that the processed passive terahertz images wereclearer and easier to identify suspicious objects than the original images. We also compare our method with three conventional methods and our method show greater advantage over the other methods.

This paper proposed a polarization independent terahertz modulator based on gold-Si metamaterials with symmetric structure, and aimed to modulate terahertz wave in communication systems. The transmission properties have been investigated in terahertz regime. We find that the resonance frequency of this device can be actively controlled by pump laser. The numerical simulations and experiments with OPTP system show that this device acts as a modulator with intensity modulation depth of 70% by gold structure.

Terahertz wave carrying OAM would boost the capacity of free-space communication with a high carrier frequency and additional degrees of freedom. In this work, we present a experimental demonstration of THz orbital angular momentum (OAM) encoding via 3D printed spiral phase plates(SPPs). By using four “coding” spps with toplogical values -2, - 1,+1,+2, we can encode OAM information onto THz waves and generate temporal varying OAM states with controlled sequences (i.e., 2-bit coding). By using interference between OAM beam and a reference gaussian beam, the OAM information can be detected from the interference fork pattern.

Terahertz (THz) imaging technology shows great advantage in nondestructive detection (NDT), since many optical opaque materials are transparent to THz waves. In this paper, we design and fabricate dielectric axicons to generate zeroth order-Bessel beams by 3D printing technology. We further present an all-electric THz imaging system using the generated Bessel beams in 100GHz. Resolution targets made of printed circuit board are imaged, and the results clearly show the extended depth of focus of Bessel beam, indicating the promise of Bessel beam for the THz NDT.

The influence of the waveguide spacing on transmission response for parallel-plate waveguide with single deep groove has been experimentally studied. The results indicate that the decrease of spacing can efficiently excite the higher order cavity modes in very deep groove. The relationship between the spacing and the channel number presents the possibility of a notch filter to mechanically select the channel number. Experimental data and simulations results verify this channel number tunibility, which may be of great interest for communication applications.