Enhanced picosecond terahertz wave generation based on cascade effects in a terahertz parametric generator

Enhanced terahertz wave generation via a Stokes cascade process has been demonstrated using picosecond pulse pumped terahertz parametric generation at 1 kHz repetition rate.Clear cascade saturation of terahertz output was observed,and the corresponding cascade-Stokes spectra were analyzed.The maximum terahertz wave average power was 22μW under a pump power of 30 W,whereas the maximum power conversion efficiency was 8×10^(-7)under a pump power of 21 W.The THz power fluctuation was measured to be about 1%in 20 min.This THz parametric source with a relatively stable output is suitable for a variety of practical applications.

Terahertz technology in intraoperative neurodiagnostics:A review

Terahertz(THz)technology offers novel opportunities in biology and medicine,thanks to the unique features of THzwave interactions with tissues and cells.Among them,we particularly notice strong sensitivity of THz waves to the tissue water,as a medium for biochemical reactions and a main endogenous marker for THz spectroscopy and imaging.Tissues of the brain have an exceptionally high content of water.This factor,along with the features of the structural organization and biochemistry of neuronal and glial tissues,makes the brain an exciting subject to study in the THz range.In this paper,progress and prospects of THz technology in neurodiagnostics are overviewed,including diagnosis of neurodegenerative disease,myelin deficit,tumors of the central nervous system(with an emphasis on brain gliomas),and traumatic brain injuries.Fundamental and applied challenges in study of the THz-wave–brain tissue interactions and development of the THz biomedical tools and systems for neurodiagnostics are discussed.

Targeted Sub-Attomole Cancer Biomarker Detection Based on Phase Singularity 2D Nanomaterial-Enhanced Plasmonic Biosensor

Detection of small cancer biomarkers with low molecular weight and a low concentration range has always been challenging yet urgent in many clinical applications such as diagnosing early-stage cancer,monitoring treatment and detecting relapse.Here,a highly enhanced plasmonic biosensor that can overcome this challenge is developed using atomically thin two-dimensional phase change nanomaterial.By precisely engineering the configuration with atomically thin materials,the phase singularity has been successfully achieved with a significantly enhanced lateral position shift effect.Based on our knowledge,it is the first experimental demonstration of a lateral position signal change>340μm at a sensing interface from all optical techniques.With this enhanced plasmonic effect,the detection limit has been experimentally demonstrated to be 10^(-15) mol L^(−1) for TNF-α cancer marker,which has been found in various human diseases including inflammatory diseases and different kinds of cancer.The as-reported novel integration of atomically thin Ge_(2)Sb_(2)Te_(5) with plasmonic substrate, which results in a phase singularity and thus a giant lateral position shift, enables the detection of cancer markers with low molecular weight at femtomolar level. These results will definitely hold promising potential in biomedical application and clinical diagnostics.

Energy scaling and extended tunability of a ring cavity terahertz parametric oscillator based on KTiOPO_(4) crystal

A wide terahertz tuning range from 0.96 THz to 7.01 THz has been demonstrated based on ring-cavity THz wave parametric oscillator with a KTiOPO_(4)(KTP)crystal.The tuning range was observed intermittently from 0.96 THz to 1.87 THz,from 3.04 THz to 3.33 THz,from 4.17 THz to 4.48 THz,from 4.78 THz to 4.97 THz,from 5.125 THz to 5.168 THz,from5.44 THz to 5.97 THz,and from 6.74 THz to 7.01 THz.The dual-Stokes wavelengths resonance phenomena were observed in some certain tuning angle ranges.Through the theoretical analysis of the dispersion curve of the KTP crystal,the intermittent THz wave tuning range and dual-wavelength Stokes waves operation during angle tuning process were explained.The theoretical analysis was in good agreement with the experiment results.The maximum THz output voltage detected by Golay cell was 1.7 V at 5.7 THz under the pump energy of 210 mJ,corresponding to the THz wave output energy of5.47μJ and conversion efficiency of 2.6×10^(-5).

High-sensitive terahertz detection by parametric up-conversion using nanosecond pulsed laser

A high-sensitive terahertz detector operating at room temperature was demonstrated based on parametric upconversion.A nanosecond 1064-nm Nd:YAG laser was used to pump the parametric up-conversion detector and the upconversion from terahertz wave to NIR laser was realized in a lithium niobate crystal.The minimum detectable terahertz energy of 9 p J was realized with the detection dynamic range of 54 d B,which was three orders of magnitude higher than that of commercial Golay cell.The detectable terahertz frequency range of the detection system was 0.90 Thz–1.83 THz.Besides,the effects of pump energy and effective gain length on the detection sensitivity were studied in experiment.The results showed that higher pump energy and longer effective gain length are helpful for improving the detection sensitivity of parametric up-conversion detector.

Investigations on the tensile deformation of pure Mg and Mg–15Gd alloy by in-situ X-ray synchrotron radiation and visco-plastic self-consistent modeling

In this study,the texture evolutions of two Mg materials during tension are explored.In-situ X-ray synchrotron and Visco-Plastic SelfConsistent(VPSC) modeling are employed to investigate the different deformation modes between pure Mg and Mg-15Gd(wt.%) alloy.These two materials with a strong extrusion texture show large different slip/twinning activity behaviors during tensile deformation.The basal(a) slip has the highest contribution to the initial stage of plastic deformation for pure Mg.During the subsequent plastic deformation,the prismatic slip is dominant due to the strong ED//(100) fiber texture.In contrast,the deformation behavior of Mg-15Gd alloy is more complex.Twinning and basal slip are dominant at the early stage of plastic deformation,but further deformation results in the increased activation of prismatic and pyramidal slips.In comparison to pure Mg,the ratios of the critical resolved shear stress(CRSS) between non-basal slip and basal slip of the Mg-15Gd alloy are much lower.

Terahertz two-pixel imaging based on complementary compressive sensing

A compact terahertz（THz） imaging system based on complementary compressive sensing has been proposed using two single-pixel detectors. By using a mechanical spatial light modulator, sampling in the transmission and reflection orientations was achieved simultaneously, which allows imaging with negative mask values. The improvement of THz image quality and anti-noise performance has been verified experimentally compared with the traditional reconstructed image, and is in good agreement with the numerical simulation. The demonstrated imaging system, with the advantages of high imaging quality and strong anti-noise property, opens up possibilities for new applications in the THz region.

基于MgO∶CLN晶体的脉冲种子注入式太赫兹波参量产生源

同成分铌酸锂(CLN)晶体是最常用的太赫兹参量增益晶体,基于该晶体的太赫兹波参量辐射源具有太赫兹波输出能量高、连续可调谐等优点,但是其调谐范围相对较窄,一般为0.6~3 THz,限制了其实际应用范围。为此,提出基于摩尔分数为5%的氧化镁掺杂的CLN晶体的脉冲种子注入式太赫兹波参量产生器,其太赫兹波频率调谐范围为1~4 THz,在2.0 THz处获得最大输出能量为1.02μJ,输出太赫兹波的3 dB带宽达1.94 THz,占调谐范围的64.67%。该太赫兹辐射源具有宽频带、增益平坦等特性,在实际应用中具有更高的价值。

High-average-power, high-repetition-rate tunable terahertz difference frequency generation with GaSe crystal pumped by 2 μm dual-wavelength intracavity KTP optical parametric oscillator

We have demonstrated a high-average-power,high-repetition-rate optical terahertz(THz)source based on difference frequency generation(DFG)in the GaSe crystal by using a near-degenerate 2μm intracavity KTP optical parametric oscillator as the pump source.The power of the 2μm dual-wavelength laser was up to 12.33 W with continuous tuning ranges of 1988.0–2196.2 nm/2278.4–2065.6 nm for two waves.Different GaSe cystal lengths have been experimentally investigated for the DFG THz source in order to optimize the THz output power,which was in good agreement with the theoretical analysis.Based on an 8 mm long GaSe crystal,the THz wave was continuously tuned from 0.21 to 3 THz.The maximum THz average power of 1.66μW was obtained at repetition rate of 10 kHz under 1.48 THz.The single pulse energy amounted to 166 pJ and the conversion efficiency from 2 μm laser to THz output was 1.68×10^(-6).The signal-to-noise ratio of the detected THz voltage was 23 dB.The acceptance angle of DFG in the GaSe crystal was measured to be 0.16°.

Large-scale scene real-time infrared simulation based on texture blending

Purpose-Infrared simulation plays an important role in small and affordable unmanned aerial vehicles.Its key and main goal is to get the infrared image of a specific target.Infrared physical model is established through a theoretical research,thus the temperature field is available.Then infrared image of a specific target can be simulated properly while taking atmosphere state and effect of infrared imaging system into account.For recent years,some research has been done in this field.Among them,the infrared simulation for large scale is still a key problem to be solved.In this passage,a method of classification based on texture blending is proposed and this method effectively solves the problem of classification of large number of images and increase the frame rate of large infrared scene rendering.The paper aims to discuss these issues.Design/methodology/approach-Mosart Atmospheric Tool(MAT)is used first to calculate data of sun radiance,skyshine radiance,path radiance,temperatures of different material which is an offline process.Then,shader in OGRE does final calculation to get simulation result and keeps a high frame rate.Considering this,the authors convert data in MAT file into textures which can be easily handled by shader.In shader responding,radiance can be indexed by information of material,vertex normal,eye and sun.Adding the effect of infrared imaging system,the final radiance distribution is obtained.At last,the authors get infrared scene by converting radiance to grayscale.Findings-In the fragment shader,fake infrared textures are used to look up temperature which can calculate radiance of itself and related radiance.Research limitations/implications-The radiance is transferred into grayscale image while considering effect of infrared imaging system.Originality/value-Simulation results show that a high frame rate can be reached while guaranteeing the fidelity.