The ultrafast photocurrents in a typical 3D topological insulator (TI) Sb₂Te₃ were probed with THz emission spectroscopy by tuning the polarization of excitation pulses and the sample’s azimuthal angle. The different ultrafast photocurrents driven by the linear photogalvanic effect, circular photogalvanic effect, and thermoelectric effect were distinguished from THz emission signal. Results potentially provide insights into the ultrafast all optical modulation of THz emission with non-external bias field, which could play a vital role in future TI-based high-speed THz optoelectronic and optospintronic devices.

The application of intelligent inspection to the online inspection of ceramic tile surface defects not only ensures the stability of product quality but also reduces the cost of labor for enterprises. Existing detection methods often achieve good results for the detection of defects in known background textures, however, its false detection rate increases dramatically, and its practicality is greatly reduced when there are unknown background textures or defects with similar characteristics to known background textures. This paper proposes a non-defective and defective samples synchronous comparison detection(N-DSCD) algorithm which combines traditional detection with deep convolutional neural network(DCNN). Firstly, a reference image library of non-defective ceramic tiles which contains all random backgrounds of the same batch of tiles is constructed based on DCNN extracting image features in real-time. After that, a reference image with the most similar features to the image to be detected is searched out from the image library relying on the feature comparison method. Next, we feed the image to be detected and the reference image to the defect detector at the same time, the difference in results is used as the basis of judging whether the ceramic tile has defects or not. Tested on a total of 12,000 images of ceramic tiles with 20 different textures found that: the computational time of a single ceramic tile increased by only 120 ms, and the average false detection rate of 20 unknown background texture tiles was reduced from 23.1% to 5.8%. It greatly improves the practicality of the ceramic tile surface defects online inspection system and has wider economic benefits.

In many precision physics experiments, due to special environmental requirements, the experiment must be carried out in a closed container, which makes it impossible to directly perform ultra-high-speed imaging measurements on a small field of view. In order to meet this demand, based on the optical fiber image bundle, this paper carried out the optical and mechanical design of the endoscopic lens, the sealed adapter lens and the ultra-high-speed camera coupling objective lens, and finally transmitted the target image to the self-developed ultra-high-speed optic-electronic framing camera. So as to realize ultra-high-speed imaging of small field of view. The resolution test and dynamic experimental verification of the designed system have been carried out. The test result shows that the surface system can achieve the high-quality imaging requirements of the small field of view on the target surface. At present, this system has been applied in related physical experiment test research.

We propose a novel patch antenna operating at 300 GHz. The antenna has a footprint of 500 μm × 500 &mum and a height of 198 &mum. The matching and radiation properties are studied. The simulation results show that the return loss (S11) is below -10 dB in the frequency range of 290.75 to 308.20 GHz and the relative bandwidth is 5.8%. At the central frequency of 300 GHz, the S11 is -16.3 dB and the gain reaches 5.34 dB. Because of the symmetry of the structure, the 2-D radiation patterns in φ=0°and φ=90° planes are almost coincident. The designed antenna has a wide -3 dBbeamwidth of 105.8° on both φ=0° and φ=90° planes.

Optical transition-edge sensor (TES) with high quantum efficiency, low dark count rate, and high energy resolution has been used in quantum information and communications. The gap distance between the fiber tip and TES has an influence on the TES performance. Here we measured the interference pattern of our optical TES devices with and without anti-reflection coating and obtain the gap distance. We also obtain the absolute reflectivity of the Ti-TESs by correcting the effect of power splitter and circulator. Our copper block shrinks ~10 μm when cooled from room temperature down to 100 mK. The measured reflectivity is consistent with the simulation taking the dielectric mirror, Ti film and anti-reflection coating into account. In addition, we study the gap distance dependence of the system efficiency, and find that it is in good agreement with the measured reflectivity at 100 mK. These analyses are useful for further improvement of TES packaging.

In this work, we experimentally investigated the terahertz optical modulation properties of the quartz-based lead perovskite halide (MAPbI3) thin film. The MAPbI3 thin film were fabricated on quartz substrate by the traditional solution spin coating method. Terahertz time-domain spectroscopy (THz-TDS) system was used to measure the terahertz wave transmission characteristics of the MAPbI3/SiO2 sample under the external optical pumping. The experimental results show that the terahertz transmittance of MAPbI₃/SiO₂ sample is obviously affected by the external optical pumping power, and the modulation depth of terahertz wave can reach more than 72.36%. The experimental study shows that the MAPbI3 thin film will be widely used in terahertz modulator, filter, photoelectric switch, photoelectric detector and so on. It has positive practical significance and good application prospect to carry out the application research of lead halide perovskite material in the field of terahertz technology.

Attribute scattering centers model (ASCM) can provide important geometric information regarding the illuminated target. However, sliding scattering center (SSC) cannot be well extracted based on the current ASCM. This paper proposes an efficient method to extract SSCs based on density-distance (DD) matching. First, the scattering characteristic of SSC is derived theoretically from the perspective of physical optical (PO). Then, the frequency dependence and estimated position are analyzed by the multi-peak model. The distance and density of each scattering center are constructed and cluster by the proposed DD -based matching algorithm. Finally, the geometrical structure corresponding to each scattering centers can be retrieved. Simulation results validate the feasibility and accuracy of the proposed method.

Terahertz waves have a wide range of applications in the field of sensing because of their good coherence, high signal-noise ratio, low radiation energy, and non-ionization. In addition, THz sensing also has the advantages of real-time, non-contact, and label-free, so it has important application in biological sensing, especially in the sensing of active biological substances. But it also has some defects, such as low sensitivity, strong water absorption, limited detection information, and poor applicability. Herein, we propose a THz time-domain polarization spectroscopy (TDPS) sensing system. The metal metasurface structures are used as the sensor, and the transmission or reflection sensing method is used to detect the PVA thin film, tumor cell and amino acid solution respectively. The experimental results show that: compared with the traditional resonant sensing method, the quality (Q) factor and figure of merit (FoM) of polarization sensing method are improved by at least 4~5 times, so the sensing sensitivity is significantly improved. For tumor cell sensing, its minimum detection accuracy has reached 10³ cells/ml. For amino acid solution sensing, the minimum detection accuracy is 10^-5 g/ml magnitude. In addition, using the chiral metasurface structure as sensor, this method can also identify the difference between the chiral enantiomer solutions of amino acids.

Phase and polarization are the basic parameters of electromagnetic wave, which can not only carry useful electromagnetic information, but also manipulate the propagation and states of light. With the development of terahertz (THz) technology and its application system, high-performance THz phase control devices are urgently needed. Our recent research work on THz phase control devices based on liquid crystals integrating with artificial microstructures or nanomaterials was reviewed in this paper. The proposed dielectric metasurface can realize a polarization-dependent electromagnetically induced transparency effect with a large artificial birefringence and a negative-dispersion phase difference with large artificial anisotropy. The double-layer graphene gratings can achieve a switchable function to switch between linear-to-linear and linear-to-circular polarization states. On this basis, we presented to combine the artificial microstructures with liquid crystals for controllable THz phase shifters and broadband wave plates. Moreover, by using the strong interaction between liquid crystals and the electrically or magnetically sensitive nanomaterials, we proposed a series of high-efficiency control THz phase devices. This work has greatly promoted the development and practical application of THz phase and polarization control devices.

As a potential ultrafast scintillator, Cl-doped γ-CuI single crystal was successfully grown in acetonitrile solvent through evaporation technique, and its crystal structure and luminescence characteristics were investigated in detail. The results of photoluminescence and X-ray excited luminescence spectra indicated that the near-band-edge (NBE) emission of the crystal was significantly enhanced, and simultaneously its deep-level (DL) emission was suppressed greatly. And the NBE emission of the crystal exhibited a sub-nanosecond decay time. It is demonstrated that a superior luminescence performance can be expected for Cl-doped γ-CuI crystal by increasing dopant concentration. This work offers a suggestion for optimizing the scintillation properties of the γ-CuI crystal.

Two-dimensional/ three-dimensional (2D/3D) van der Waals (vdW) heterostructures are one of the most potential candidates for table-top pulse terahertz (THz) emitters. Hence, manipulating carrier information at the interface is important to optimize THz emission performance. Photoinduced doping is an effective way to embellish the carrier characteristic at the interface. Here, we applied the photoinduced doping effect to dynamically manipulate the THz generation process from graphene-silicon (Gr-Si) heterostructure. When photoinduced doping is applied by using 532 nm continuous wave (CW) laser, THz radiation decreases with the increase of CW pump power at the reverse bias. The photoinduced doping attenuates the interfacial built-in electric field, resulting in the decrease of transient photocurrent and further reduction of THz radiation. This photogenerated carrier screening effect has achieved a 95.4% intrinsic THz modulation depth (MD) at the external excitation of 200 mW CW laser under reverse bias voltage -30 V. The intrinsic THz MD is much higher than previous report value due to the optimized heterostructure fabrication and the optimized light spot overlap of CW laser and femtosecond laser. This work proposes a non-destructive and reversible method to actively manipulate the THz emission at the vdW interface and provides an optimized route to realize high intrinsic THz MD in THz region.

Extracting spectral parameters of materials is an essential application of terahertz spectroscopy technology, based on the characteristics of coherent detection. However, the commonly used algorithm for extracting spectral parameters requires a parallel and smooth surface as a prerequisite, and the surface roughness will affect the extraction result. Nevertheless, the effect degree and the mechanism are not precise before. Firstly, in this research, optical parameters of samples with different roughness extracted by the algorithm are displayed. Therefore, the effect degree of different roughness on the optical extraction algorithm is clarified. After that, the mechanism of the influence is analyzed through the method of microelement modeling. As a result, it shows that when the sample surface is slightly rough (roughness<60μm), it will not significantly impact the extraction results. The shape of the optical curve will not be significantly distorted. As the roughness increases, the change of the statistical distribution of the Fresnel coefficient and the phase change are the reason for the attenuation of the terahertz wave amplitude and the decrease of the extraction accuracy.

We report the optical response of layered bulk and monolayer SnS₂ at the surface. The physical mechanism for terahertz (THz) emission in bulk and monolayer SnS₂ has been proposed. At 40° incident angle, the drift current accompanied by the surface nonlinear polarization concurrently contribute to THz surface emission in bulk SnS_2. The THz radiation in monolayer SnS₂ is mainly attributed to the drift photocurrent, which is insensitive to the crystalline symmetry and the pump polarization direction. The corresponding investigation could not only help to clarify the relationship of layer-dependent optical properties, but also make a significant contribution in understanding the nonlinear physical process in other transition metal dichalcogenides (TMDs) materials.

The plasma sheaths generated by vehicles flying at hypersonic speed in the near space will interact with electromagnetic waves. This creates series of problems to communication and detection. Terahertz (THz) technology holds large potential in solving the problems caused by the plasma sheath for its special characteristics. However, due to the limitation in computation capability and experimental equipment, the research on the radar cross section (RCS) of the target covered with the inhomogeneous plasma sheath in THz band is still insufficient. The echo attenuation is the basis of considering the RCS attenuation, so studying echo attenuation characteristics can provide support for further study of radar scattering characteristics. In this paper, a simplified calculation method is proposed to analyze the echo attenuation characteristics of a vehicle covered with the inhomogeneous plasma sheath in THz band. Firstly, the echo attenuation model of the target covered with the inhomogeneous plasma sheath is established. Then, considering that the total echoes include the echoes reflected by the surface of the plasma sheath and reflected by the target surface through the plasma sheath, the calculation process of the total echo attenuation is derived. The variations of echo attenuation with THz frequency, plasma electron density, plasma collision frequency and incident angle are further studied. The results validate that the shielding effect of the plasma sheath is weakened in the THz spectrum. This indicates the great prospect of THz technology in the communication and detection of hypersonic vehicles in the future.

The advances in electron accelerator science and technology continue to reach shorter bunch lengths, even down to femtosecond, paving a way to generate coherent Smith-Purcell radiation naturally, taken as one of the most promising THz sources. In order to design a high power and broadly tunable THz radiation source, we make theoretical and numerical analysis of the characteristic of coherent Smith-Purcell radiation, which demonstrates good agreement between them. In the paper, we also present the comparison of spectra of coherent Smith-Purcell produced from the interaction of a single bunch and a train of microbunches.

Multiple filaments generation and manipulation are crucial to numerous applications. The refractive index of medium has essentially influenced nonlinear effects in the ultrafast optical process of femtosecond laser filamentation, which is an effective method to tailor and manipulate filamentation. We have proposed a new method that using a periodic gas lattice as transmission medium to generate multiple filaments of femtosecond laser pulse. The periodic gas lattice is consisted of air waveguides, which has the special refractive index change distribution with alternating positive and negative. Our results show that the properties of multi-filament can be well controlled by changing the parameters of the gas lattice. A multi-filament array is formed by the gas lattice along the beam propagation direction, which are systemically investigated with different parameters of lattice at filamentation stages. The underlying physical mechanism of the multi-filament array formation is discussed, which has been demonstrated that the effects of extra focusing and discrete diffraction introduced by the gas lattice medium to promote a new competition and balance in the nonlinear filamentation process. The findings in this work provide a new way for many potential and promising applications that based on the controlled and optimized the femtosecond laser multi-filament array.

Turbulence is ubiquitous in ambient air and has always posed a great challenge for realizing optical applications in the atmosphere. The refractive index of turbulent air fluctuates randomly has obviously influences on the nonlinear process and characteristics of filamentation, which is a crucial role for many practical applications in free-space atmosphere. In the numerical simulation, we have investigated the filamentation and supercontinuum generation of femtosecond laser pulse with strong atmospheric turbulence in the path of whole the propagation distance. The spatial profile of intensity is analyzed in detail by changing perturbation strength of turbulence. The results show that the laser energy flow distribution presents stronger optical modulation instability with the increase of turbulence intensity in air. Complex spatial multifilament structures are generated by nonlinear propagation in strong turbulent air. The optical intensity along propagation distance significantly decrease as the strength of turbulence increases. The supercontinuum spectrum of filamentation in different strengths turbulence is also investigated. The physical mechanism of supercontinuum intensity change with different strengths of turbulence is discussed. Our results are valuable for realizing the free-space applications based on filamentation and supercontinuum in extreme weather with strong turbulence.

In the terahertz (THz) band, the scaling relation between scaled models and prototypes with coatings needs to be reconsidered due to the dispersive nature of the coating materials. Besides, it is difficult to obtain the material parameters, such as the permittivity. Based on the comparison of RCS between a metal plate and a coated plate, a key parameter extraction method is proposed. Combining with the scaled method which is based on the dimensional analysis theory, an improved scaled method is proposed for predicting the RCS of a coated prototype. The parameter extraction method can provide the key parameter corresponding to the coated material at certain frequency when the intrinsic parameters are unknown. The validity of the proposed method is proved by simulation. The scope of RCS scaled measurements on coated targets will be expanded in the THz band.

China Academy of Engineering Physics Terahertz Free Electron Laser (CTFEL) has been commissioned in 2017 and provides 0.7~4.2 THz wave for users. In order to cover the frequency range of 0.1~0.7 THz, a super-radiation terahertz source is designed behind CTFEL. In this paper, design of the super-radiation source is reported. The super-radiation source works with MeVs and sub-picosecond electron bunch. The technical route to generate MeVs and sub-picosecond is as follows: the superconducting accelerator of CTFEL has two independent 4-cell cavities, the electron beam is accelerated in the first 4-cell cavity, and compressed in the second 4-cell cavity. The sub-picosecond electron beam travels through a undulator with a period of 58 mm to generate terahertz wave, and the gap of the undulator is adjusted to cover the frequency range of 0.1~0.7 THz. The theoretical calculation shows that average power of the super-radiation source can reach tens of Walt.

Brain glioma is the most frequent primary tumor of the nervous system, and has serious adverse effects on public health and social economy. A technique that can be used to precisely detect glioma is highly demanded. Here, we report on that the terahertz time-domain spectroscopy, a rapid, label-free and non-destructive technique, was utilized to probe mouse tissue slices containing glioma. The results show that the glioma can be discriminated in the frequency range of 0.7-1.6 THz on the basis that the refractive index as well as the absorption coefficient of glioma are higher than the normal tissue, which can be attributed to the higher cell density and water content of the glioma. The present work validates that it is feasible to detect glioma with a terahertz time-domain spectroscopy technique.

We theoretically and experimentally demonstrate the influence of dispersion on the temporal mode properties of the spontaneous Raman scattering pumped by picosecond pulses in single mode optical fiber. We model the process of the ultrafast spontaneous Raman scattering, calculate and measure the intensity correlation function of the Raman photons with different dispersion by varying the detuning between pump and Raman photons or changing the optical length. The intensity correlation function decreases with the increase of dispersion induced temporal walk-off both by increasing the detuning and by increasing the fiber length. We evaluate the dispersion parameter of the single mode fiber by fitting the measured data with the theoretical equation we deduced. The estimated value is close to the labelled one. Our study provides a new way to evaluate dispersion parameters of the media in which Raman scattering can occur and is beneficial for efficient distillation of entanglement in optical fibers.

Highly uniform and densely packed ZnO nanowire arrays have been successfully synthesized by a low hydrothermal method combined with Anodic Aluminum Oxide (AAO) template-filling method, and their morphology, structure and luminescence property were investigated in detail. The scanning electron microscopy images indicates that the ZnO nanowire arrays are highly ordered and their diameter and length are about 0.4 and 60 μm, respectively, precisely defined by the pore of the AAO template. Simultaneously, the ZnO nanowire arrays are indexed to hexagonal wurtzite polycrystalline as revealed by X-ray diffraction patterns. The photoluminescence spectrum of ZnO nanowire arrays is resolved into two bands centered at about 470 nm and 510 nm, and which are originated from AAO template and the oxygen vacancies of ZnO nanowire arrays, respectively. It is expected that the ZnO nanowire arrays within AAO template is a promising candidate for development of radiation detection and imaging with ultrafast and high-spatial-resolution.

A VO₂ -based Terahertz metasurface is proposed, and the cell structure consists of two parts. One part is composed of VO₂ blocks connected by metal rings with different radius, and the other part is a VO₂ square ring. The conductance coupling between the metal structures can be manipulated by the metal-insulator phase transition of VO₂ to change the LSPR resonance mode. The transformation realizes active tunable dual-band absorption of the terahertz wave, and the effects of incident wave angle and polarization mode on the frequency response characteristics of the structure are investigated respectively. Subsequently, the theoretical study on the Terahertz metamaterial absorber is carried out, and the results indicate that the two absorption peaks are generated by the autonomous resonance of gold rings with different radius when the temperature is 25°C The absorption rate of the absorber can reach 98% and 92% at f THz = 4.16 and f THz = 5.75 , respectively. When the temperature exceeds the VO₂ phase transition temperature (68°C), the VO₂ block is combined with metal rings of different radius to form a current closed-loop which would cause unified resonance and coupling with the VO₂ square ring. Meanwhile, the absorption rate of the absorber can reach 90% at f THz = 5.27 and f THz = 8.5 . In addition, the influence of the external dielectric constant and structural parameters on the absorption characteristics is analyzed, and the applications of the absorber in sensing and thickness detection are explored to obtain the responding sensing detection performance. The conclusions are beneficial for the design of actively tunable Terahertz metasurface absorbers and have many potential applications in the detection field.

In this paper, the broadband absorption and narrowband absorption conversion can be achieved by introducing vanadium dioxide from the insulator to metal phase transition. The absorption tunable terahertz metamaterial device is composed of vanadium dioxide metasurface, silica spacer, vanadium dioxide film, patterned metal layer, silica spacer and metal substrate form the top to the bottom. The simulations demonstrate that the device can efficiently absorb more than 90% of the energy in the frequency range of 1.20-2.29 THz when the vanadium dioxide is in its fully metal state. The broadband performance is sustained over a wide range of incident angles, and is also insensitive to polarization due to the symmetry. However, as the vanadium dioxide is in its insulate state, the device behaves as a multi-narrowband absorber and absorbs over 95% of the incident power at 0.506, 1.022, 1.703, 1.967 THz, respectively. The narrowband performance is maintained over a wide range of incident angles. Furthermore, the influence of the different geometrical parameters on the absorptance performance is discussed. The proposed tunable absorber can be used in various applications, such as modulating, sensing and imaging technology.

Metamaterials has shown outstanding flexibility and functionality in optics and electromagnetics, which attracted plenty of interest. Nested ring resonators have a wide range of applications in terahertz (THz) spectroscopy, sensing and communication. Hence, we design a kind of metamaterials structure which can modulate THz transmission and resonance. It consists of a circular split ring resonator (CSRR) inside a closed square ring resonator. The single CSRR has an inductive-capacitive (LC) resonance and the single closed square ring resonator has a dipole resonance. After nesting two resonators, the resonance mode is changed from single mode to double modes. The results show that the amplitude transmission of non-resonant region is related to the gap opening and the asymmetry of structure. The amplitude transmission of resonance region depends on the conductivity of substrate. With the gap opening of CSRR increases, the amplitude transmission of non-resonant region increase. Meanwhile, the frequency of resonance has an obvious blue-shift. With the bottom edge distance of the two resonators decreases(the asymmetry increases), the amplitude transmission of the non-resonant region increases gradually and the low frequency of resonance has a red-shift and the high frequency of resonance has a blue-shift. To further analyze the influence of conductivity of substrate on amplitude transmission, we change the conductivity of substrate during the simulation. The results demonstrate that with the conductivity of the substrate increases, the resonance absorption peak decreases until disappears, the amplitude transmission of the non-resonant region decreases. Our results may have the potential applications in THz modulator.

We modulate the electromagnetic response of terahertz metamaterials by exciting photogenerated carriers with ultra-short pulsed laser, and realize the active control of terahertz transmission and resonances in a wide band. The experimental results show that when the terahertz electric vector is perpendicular and parallel to the bar direction with the open gap in the circular split ring resonators, respectively, the transmission of the non-resonant region and resonance absorption are significantly tuned by the irradiated pump pulse. With the increase of the pump power, the resonance absorption peak decreases and the frequency of resonance dip has a remarkable blue-shift. Meanwhile, the transmission of the non-resonant region decreases correspondingly. It is also found that the blue-shift of the resonance is mainly determined by the change of conductivity and dielectric constant in the photoexcited layer of the substrate. Through the numerical simulation, we have further proved the introduction of pump light has a significant modulation effect on the electromagnetic properties of terahertz metamaterials. Additionally, it can be observed that the LC resonance annihilates earlier than the resonance of the dipole resonance with the increase of pump power, implying the former is particularly sensitive to the variation of the active control. In the theoretical analysis, based on the Lorenz oscillator model, we have derived and calculated the resonance response intensity of the coupled oscillators under an external field. The calculated results indicate the coupling coefficient and damping rate have an impact on the spectra evolution, showing that the resonant response peak has a remarkable blue-shift with the increase of coupling coefficient and the resonance response intensity decreases with the increase of damping rate.

Precise X-ray Imaging diagnostics to acquire the plasma state and its evolution plays an important role in basic researches such as inertial confinement fusion (ICF), high energy density physics (HEDP), and another ultrafast phenomenon. The plasma signals with the characteristics of small scale, rapid evolution and complex spectrum requires the X-ray diagnostics optics to have high spatial resolution and collection efficiency, as well as certain spectral resolution. The multilayer Kirkpatrick–Baez (KB) microscope is a common X-ray optics to obtain high spatial, collecting efficiency or spectral resolution. Coupling multichannel KB microscope with the framing camera, the temporal evolution behavior of the ultrafast plasma can be recorded. The paper mainly presents our latest research on two-energy sixteen-channel multilayer KB microscope for double-cone ignition (DCI) experiments, including its optical and multilayer design. By high-resolution backlighting and self-emission imaging using two-energy multichannel KB microscope, plasma information related to density and temperature can be realized simultaneously.

An Ultrafast Electron Diffraction (UED) based on an RF photocathode electron gun has the advantage of producing MeV relativistic probing electron beams, which can maintain a high time resolution of ~100 fs while keeping more electrons to improve the S/R ratio of the image. However, the jitter of driving RF power in the electron gun between pulse to pulse has an indispensable impact on the electron energy stability leading to the Time of Flight (ToF) jitter, which creates asynchronization between the pump laser and the probing electron worsening the time resolution. To stabilize the beam energy to the designed value 3 MeV and reduce the ToF jitter further, we propose controlling the electron energy based on an energy spectrometer directly. An electron spectrometer based on a C-type dipole is being designed to achieve high energy resolution. This paper will introduce the design of the energy spectrometer, and particle tracking is implemented to demonstrate the feasibility of the design.

With strong optical response from subwavelength metamaterial structures in terahertz, plasmon-induced transparency (PIT) has attracted considerable attention in terahertz modulators and biosensing devices. Here, we tune PIT effect by the destructive interference of two bright modes. We design a terahertz metamaterials structure with triple U-shaped resonators (TUR) arrays. In the vertical direction, double U-shaped resonators (DUR) are arranged downward, single-U resonator (SUR) is upward. We change the length of the SUR, the inner arms of the DUR and the horizontal distance of the DUR in order to observe the terahertz transmission spectrum. It is found from the results that with the length of the SUR increases， the resonant frequency has an obvious red-shift, the absorption of the low-frequency resonance increases and the nonresonance absorption peak gradually decreases. As the arms of the DUR increase and the distance between them decreases in horizontal, the frequency of resonance dip has a red-shift, and the transmittance of the non-resonant region increases slightly. To explore the influence of dielectric environment on the resonance characteristics of the terahertz metamaterials, we have further performed the simulations with the applied surface analyte of different refractive index. The results show that with the increase of the refractive index of the surface of the analyte, the resonance frequency has a more significant red-shift. Our obtained results could provide the idea for designing terahertz modulators and sensitive biosensing devices.

Highly sensitive response of anisotropic terahertz metamaterials to electromagnetic waves has attracted considerable attention due to its potential applications in terahertz modulators and biosensing devices. We designed three microstructure samples with split ring arrays. The terahertz transmission spectra are experimentally measured at different rotation angle. It is found that as the rotation angle increases, the resonance mode has gradually evolved from a single dipole oscillation mode to the double oscillation modes accompanied with LC and dipole oscillations, we further simulated the polarization conversion characteristics of the single splitting rings. It shows that the highest conversion efficiency appears at 45 degrees. But it doesn’t have polarization conversion effect at 0° and 90°. Subsequently, we have utilized ultrashort pulse laser to optically control the electromagnetic response by exciting the photogenerated carriers in the metamaterial samples. The experimental data show that the transmittance change obviously with the pump light. Additionally, when the angle is 90 degrees, it can be observed that the LC resonance annihilates earlier than the resonance of the dipole resonance with the increase of pump power, implying the former is particularly sensitive to the variation of the dielectric environment. To further explore the influence of dielectric environment on the resonance characteristics of the terahertz metamaterials, we have further performed the simulations with the applied surface analyte of different refractive index. The simulated data show that with the increase of the refractive index of the surface analyte, the resonance frequency of the dipole oscillation has a more significant blue shift than the resonance frequency of the LC oscillation. Our obtained results could provide the idea for designing terahertz modulators and sensitive biosensing devices.

Spinel ferrite has the excellent characteristics of high saturation magnetization, high resistivity and low dielectric loss. It plays an important role in signal isolation, circulation, phase shift, frequency limiting, filtering, delay and amplification. So it is of great significance to study the spectral characteristics of spinel ferrite at different temperatures by using terahertz time-domain spectroscopy. The terahertz spectral characteristics of spinel ferrite under the different temperature condition were measured by terahertz time domain spectroscopy system. The transmittance of the power, absorption rate, absorption coefficient and refractive index of spinel ferrite were obtained by calculation. The experimental results show that the transmittance is positively correlated with temperature and the absorption spectrum of the samples increases with the increase of frequency in the 0-1THz band, and the refractive index of spinel ferrite increases with the increase of temperature.

In this paper, an inverse neural network based on deep learning is constructed to predict the metasurface structure of the designed terahertz metagrating. The transmittance spectra results from the numerical simulation of the metagrating were used as the input datasets for the inverse neural network, and the output is the corresponding metagrating structure parameters. After training, our inverse network can meet our expectations. The results show that some of the structural parameters predicted by the network are roughly consistent with the actual structural parameters, which indicates that the neural network can predict the corresponding structural parameters by given spectra. This has great application value, for example, it can be used to guide the design of metasurfaces for faster and more convenient purposes.

Terahertz waves have potential of non-thermal regulation of cell physiological activities. Especially, the non-thermal effects of strong field terahertz pulses on the physical and chemical properties of cells and membrane structure need to be studied in detail. Therefore, this article uses the finite element method (FEM) to simulate and study the effects of strong field terahertz pulses on the cell membrane and nucleus membrane of cells. The simulation results show that both the single-frequency terahertz wave generated by CTFEL and wide-band terahertz pulses generated by lithium niobate crystal could cause a huge potential difference between cell membrane and nucleus membrane of the suspended spherical cell, which might lead to electroporation of the cell membrane or nucleus membrane.

Non-thermal tumor ablation technology based on short pulse strong electric field can overcome the defects of thermal ablation and cryoablation, which provides a new opportunity for the development of tumor therapy. In this study, the CAEP terahertz free electron laser facility was preliminarily used to do the research on non-thermal tumor ablation method because of its unique macro-micro pulse time series. The biological effects of short pulse strong field terahertz radiation on melanoma cells and tissues were studied in vitro and in vivo. In vitro experiments show that the survival rate of tumor cells is significantly different after being irradiated by different frequency, power, and radiation duration of terahertz wave. Strong field terahertz wave can inhibit the proliferation of tumor cells. In vivo experiments showed that compared with the control group, the tumor tissue proliferation of the irradiated experimental group was slowed down, the tumor volume was gradually reduced, and the strong field terahertz pulses could inhibit the growth of tumor tissue. These preliminary results will provide a feasible reference for further research and long-term clinical application.

THz-TDS systems are widely used in non-destructive inspection and chemical inspection and are receiving increasing recognition due to its wide spectrum and the ability to distinguish isomers that can not be easily identified by other types of spectrum. Convolutional neural network is the state-of-the-art technique for feature extraction and classification of single-dimensional and multidimensional matrices and is applicable to identify the THz absorption spectrum of chemicals. We present a method based on a CNN to identify the THz absorption spectrum of several types of amino acids measured by transmission spectroscopy of a THz-TDS system and receive a rate of accuracy close to 100% even for isomers such as L-Tyrosine and DL-Tyrosine. We also present the initial results of quantitatively identifying the amino acids in a mixture, which is among the first outcomes of such research. This technology will support the future application of THz-TDS in drug detection under complex states and environments.