Spinning-disk self-referencing interferometry of antigen-antibody recognition

A gold ridge microstructure fabricated to a height of lambda/8 on a high-reflectivity substrate behaves as a wave-front-splitting self-referencing interferometer in phase quadrature when illuminated by a Gaussian laser beam and observed in the far field along the optic axis. When immuno-gammaglobulin (IgG) antibodies are selectively immobilized on the gold microstructure, they recognize and bind to a specific antigen, which shifts the relative optical phase of the interferometer and modifies the far-field diffracted intensity. We detect bound antigen interferometrically on spinning disks at a sampling rate of 100 kHz and verify the interferometric nature of the signal by using two quadratures of opposite sign to rule out effects of dynamic light scattering. Strong molecular recognition is demonstrated by the absence of binding to nontarget molecules but strong signal change in response to a specific antigen. This BioCD has the potential to be applied as a spinning-disk interferometric immunoassay and biosensor.     

Surface Emitting THz Wave Parametrical Oscillator Using MgO：LiNbO3

Room-temperature operation terahertz （THz） wave source is demonstrated using three MgO：LiNbO3 crystals which have a noncollinear arrangement. The experimental results show that the THz wave can be tunable from 0.8 THz to 3.0 THz, and the peak energy output is 103 pJ/pulse at 1.5 THz. The noncoilinear cavity configuration makes the THz beam have Gaussian-like spatial distribution, small divergence angle, perpendicularly eradiated from the crystal surface. The beam quality factor M2 is measured to be Mx^2 = 1.15, Mx^2 = 1.25 for characterizing the THz wave beam. Experiments also show that the THz beam can be focused by using a polyethylene lens, and the focal spot size is close to the diffraction limit.     

FREE VIBRATION ANALYSIS OF A SPINNING FLEXIBLE DISK-SPINDLE SYSTEM SUPPORTED BY BALL BEARING AND FLEXIBLE SHAFT USING THE FINITE ELEMENT METHOD AND SUBSTRUCTURE SYNTHESIS

Free vibration of a spinning flexible disk-spindle system supported by ball bearing and flexible shaft is analyzed by using Hamilton's principle, FEM and substructure synthesis. The spinning disk is described by using the Kirchhoff plate theory and von Karman non-linear strain. The rotating spindle and stationary shaft are modelled by Rayleigh beam and Euler beam respectively. Using Hamilton's principle and including the rigid body translation and tilting motion, partial differential equations of motion of the spinning flexible disk and spindle are derived consistently to satisfy the geometric compatibility in the internal boundary between substructures. FEM is used to discretize the derived governing equations, and substructure synthesis is introduced to assemble each component of the disk-spindle-bearing-shaft system. The developed method is applied to the spindle system of a computer hard disk drive with three disks, and modal testing is performed to verify the simulation results. The simulation result agrees very well with the experimental one. This research investigates critical design parameters in an HDD spindle system, i.e., the non-linearity of a spinning disk and the flexibility and boundary condition of a stationary shaft, to predict the free vibration characteristics accurately. The proposed method may be effectively applied to predict the vibration characteristics of a spinning flexible disk-spindle system supported by ball bearing and flexible shaft in the various forms of computer storage device, i.e., FDD, CD, HDD and DVD.     

二维太赫兹探测成像光学系统设计

二维太赫兹探测成像适用于以太赫兹波作为探测波的安全检查和质量控制等方面。为实现大视场的二维太赫兹探测成像光学系统设计,根据匹兹万条件,分析了光学三反系统面型,并提出了一种反远距离轴三反结构,设计了视场角为20°×20°,焦距为70mm,F数为3.5的离轴三反光学系统。设计结果表明,该光学系统调制传递函数接近衍射极限,各个视场的点列图均方根半径均远小于艾里斑半径,具有良好的成像质量,满足设计要求。     

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.     

Characterizing the polarity of a few-cycle infrared laser pulse

We demonstrate the characterization of polarity and carrier-envelope (CE) phase of a linearly polarized few-cycle infrared (IR) laser pulse (12?fs, 1.8???m) using Terahertz (THz) emission spectroscopy. Crossed polarizers electro-optic sampling geometry is applied to record temporal waveforms of far field THz emission from air filament driven by the few-cycle IR pulse. The THz waveforms are dependent on the carrier-envelope (CE) phase periodically. We confirm that the THz waveform and the intensity can be used jointly to determine the phase of a few-cycle laser field in laboratory frame.     

Transient-Pulse Nonlinear Spectroscopy with the Radiation of a Multimode THz Gas Laser

We report on transient-pulse nonlinear spectroscopy with the radiation of a multimode THz gas laser. The method is demonstrated for studying the nonlinear response of a current-carrying superlattice to THz radiation; the current through a superlattice can be suppressed by a strong THz field. The method makes use of the pulses of a high power multimode THz gas laser. By splitting the laser beam for selected laser modes into a main beam and a reference beam we monitored with a reference detector the transient power in the main beam. The simultaneous measurement of both the instantaneous response and the instantaneous power allows to obtain the power dependence of the response within a single laser pulse. The method is suitable to study the nonlinear response of matter to THz radiation fields in a large dynamic range.     

Terahertz-wave parametric oscillator with a misalignment-resistant tuning cavity

We demonstrate a terahertz-wave parametric oscillator (TPO) with a corner-cube resonator consisting of a corner-cube prism (CCP) and a flat mirror. By using the cavity configuration proposed in this Letter, the generation of tunable monochromatic terahertz (THz) waves can be achieved just by rotating the flat mirror instead of rotating the TPO cavity relative to the pump beam. The THz-wave output intensity and pulse width can be controlled periodically by rotating the CCP around the cavity axis. The TPO stability against cavity misalignment is significantly improved by at least 1 to 2 orders of magnitude compared with the conventional plane-parallel resonator configuration.     

Terahertz dichroism of MBBA liquid crystal on rubbed substrate

Terahertz (THz) dichroism of a nematic liquid N-(p-methoxybenzylidene)-p-butylaniline (MBBA) was measured using a GaP Raman THz spectrometer. MBBA on a rubbed plastic substrate generates a band at around 4.0 THz: its liquid crystal phase shows strong dichroism, which well corresponds to that of the IR absorption caused by π(CH) of MBBA molecule reported in the literature. Based on inferences drawn from the present THz and the published IR dichroic results, the 4.0 THz band probably stems from lateral intermolecular or intramolecular interactions of MBBA molecules aligned to the rubbing direction. The results clearly demonstrate that THz spectroscopy is powerful for discussing of phase transition and dichroism of liquid crystals.     

High-resolution GaP Terahertz Spectrometer and Its Application to Detect Defects in Gamma-irradiated Glucose Crystal

We developed high-resolution GaP THz signal generator using Cr:Forsterite lasers with gratings as both a pump and a signal beam for difference-frequency generation. A line width of less than 500 MHz and a wide tunable frequency range (0.6–6.2 THz) provide sufficient resolution for measuring materials with sharp absorption bands using the generator as the light source for a THz spectrometer. This is suitable for materials such as gases or solid samples at low temperatures. We demonstrated the detection of defects in organic materials, as they appear as slight deviations in the absorption frequency in the THz region.     

THz generation via optical rectification with ultrashort laser pulse focused to a line

We report on efficient THz pulse generation via optical rectification with femtosecond laser pulses focused to a line by a cylindrical lens. This configuration provides phase-matched conditions in the superluminal regime. 35 pJ THz pulses have been generated with this technique in a stoichiometric LiNbO₃ crystal pumped by 2 μJ femtosecond laser pulses at room temperature. An unusual superquadratic rise of the THz pulse energy with the laser pulse energy has been observed at high laser energies. This extraordinary energy dependence of the THz generation efficiency is explained by self-focusing of the laser beam in the crystal. Z-scan measurements and comparison of the THz pulse spectra created with laser pulses having different energies confirm this interpretation.     

一种新型THz显微探测技术

由于太赫兹(THz)电磁辐射的波长较长，探测的空间分辨率受到衍射极限的限制.设计了一种 新型的THz显微探测技术，使探测晶体紧贴在薄产生晶体上，激发光采用紧聚焦的方式不但 把空间分辨率提高到光学量级，还克服了典型近场探测方法中存在的低通光量、高通滤波的 缺点.详细介绍了这一新型探测器件的基本结构和显著的探测特性. 关键词： THz 近场 聚焦     

高性能85mm短腔光学参变振荡器的THz电磁波输出特性分析

报道了以MgO∶LiNbO3为非线性光学介质,采用85 mm长的法布里珀罗单谐振腔结构形式的光学参变振荡器,产生THz电磁波的实验结果。使用波长为1064 nm的Nd∶YAGQ开关脉冲激光器作为抽运光源,通过改变入射角度使参变振荡器的相位匹配条件发生变化。采用Si真空量热器,并利用THz波干涉测量仪;或通过测量闲频光的频率对产生的THz波频率进行了测量。实验表明该参变振荡器输出频率调谐范围为0.9~3.0 THz。在抽运光能量为20 mJ/pulse,脉冲宽度16 ns,重复频率50 Hz条件下得到输出峰值位于1.2 THz,能量为102.5 PJ/pulse的THz波输出。通过引入Si棱镜阵列减小了THz波在晶体中的全反射,从而提高THz波的能量输出。使用金属缝隙探测器,对辐射的THz波的波束水平方向空间分布进行了测量,分析了Si棱镜阵列的衍射效应对THz波束空间分布的影响。     

Real-time two-dimensional terahertz tomography of moving objects

We propose real-time two-dimensional (2D) terahertz (THz) tomography for 2D cross-sectional imaging of moving objects. The proposed method does not require mechanical scanning elements for time delay and sample position, which are essential for conventional THz tomography. For this purpose, a 2D spatiotemporal THz image is acquired at a frame rate of 10 frame/s by a combination of time-to-space conversion using non-collinear 2D free-space electro-optic sampling and line focusing of a THz beam on a sample. We demonstrate the use of real-time 2D THz tomography for real-time monitoring of the paint thickness in a moving paint sample and the drying progress in a wet paint film. The proposed method provides a powerful tool for non-ionizing and non-contact probing in the fields of nondestructive testing and biomedical diagnostics.     

小型化外腔可调谐THz参量振荡器

基于LiNbO3晶体垂直表面输出技术,设计了一台小型化外腔THz参量振荡器。利用小型化灯1064 nm脉冲激光器泵浦MgO:LiNbO3,通过优化设计三波非共线相位匹配的光学参量振荡腔结构,实现THz垂直晶体表面输出,减少LiNbO3晶体对THz波的吸收,提高了THz波输出光束质量。当在泵浦光能量为128 mJ、重复频率为10 Hz时,获得THz波的调谐范围为0.69~3.01 THz,在1.6 THz处获得THz波最大平均功率为10.8 W,脉冲宽度为10 ns,对应THz波能量转换效率为8.4310-6。     

Widely tunable terahertz-wave generation using an N-benzyl-2-methyl-4-nitroaniline crystal

Widely tunable terahertz (THz)-wave generation using difference frequency generation (DFG) in an organic N-benzyl-2-methyl-4-nitroaniline (BNA) crystal was demonstrated. To our knowledge, this is the first report of THz-wave generation by BNA DFG. Large, high-quality single crystals of BNA (phi 8 mm x 30 mm) were grown using the vertical Bridgman method. The nonlinear optical (NLO) coefficient d(33) of the BNA crystal is approximately 234 pm/V, which is the largest value reported for any yellow NLO material. The collinear phase-matching condition of the type-0 configuration is satisfied using a 0.7-1 microm band pump wavelength. We generated THz waves using an organic BNA crystal; the generation range is 0.1-15 THz.     

Acoustic rotational manipulation using orbital angular momentum transfer

We report on the first quantitative test of acoustic orbital angular momentum transfer to a sound absorbing object immersed in a viscous liquid. This is done by realizing an original experiment that is to spin a millimeter-size target disk using an ultrasonic vortex beam. We demonstrate the balance between the acoustic radiation torque calculated from the Brillouin stress tensor and the viscous torque evaluated from the steady state spinning frequency. Moreover, we unveil a rotational acoustic streaming phenomenon that results from the acoustic angular momentum transfer to the host fluid. We show that it lowers the viscous torque, thereby restoring the torque balance.     

Experimental characterization of bi-directional terahertz emission from gold-coated nanogratings

The THz radiation emission of Au-coated nanogratings (fused silica substrate, 30?nm Au layer thickness, 500?nm grating constant) upon fs laser irradiation (785?nm, 150?fs, 1?kHz,???1?mJ/pulse) is observed in both directions along the laser beam axis (forward and backward) and for both, illumination of the Au/air or the Au/silica interface. THz radiation along the laser beam propagation is emitted in a narrow solid angle of about 15°?fwhm independent on the laser pulse fluence, the angle of incidence and the nanograting profile. The bar width and groove depth of the nanograting as well as the angle of laser beam incidence strongly affect the THz radiation yield. The energy of single THz light pulses is measured absolutely (2?fJ in the 0.3?C0.38?THz range) using a highly sensitive and fast superconducting transition edge sensor. The bi-directional emission of THz radiation is in agreement with the model assumption of surface plasmon polaritons propagating simultaneously on both Au layer interfaces (Au/air and Au/silica).     

Tunable few-cycle and multicycle coherent terahertz radiation from relativistic electrons

We report the generation of tunable, narrow-band, few-cycle and multicycle coherent terahertz (THz) pulses from a temporally modulated relativistic electron beam. We demonstrate that the frequency of the THz radiation and the number of the oscillation cycles of the THz electric field can be tuned by changing the modulation period of the electron beam through a temporally shaped photocathode drive laser. The central frequency of the THz spectrum is tunable from ～0.26 to 2.6 THz with a bandwidth of ～0.16 THz.     

Rapid Frequency-Domain FLIM Spinning Disk Confocal Microscope: Lifetime Resolution,Image Improvement and Wavelet Analysis

A spinning disk confocal attachment is added to a full-field real-time frequency-domain fluorescence lifetime-resolved imaging microscope (FLIM). This provides confocal 3-D imaging while retaining all the characteristics of the normal 2-D FLIM. The spinning disk arrangement allows us to retain the speed of the normal 2-D full field FLIM while gaining true 3-D resolution. We also introduce the use of wavelet image transformations into the FLIM analysis. Wavelets prove useful for selecting objects according to their morphology, denoising and background subtraction. The performance of the instrument and the analysis routines are tested with quantitative physical samples and examples are presented with complex biological samples.