Double-line terawatt OPCPA laser system for exciting beat wave oscillations

A double-line terawatt beat laser (BEAT) is developed for exciting beat wave oscillations. BEAT consists of two oscillators and an amplification system including optical parametric chirped-pulse amplification (OPCPA) in which two individual pulses with wavelength separations of 10–35 nm are amplified, recompressed, and focused as a single beam. The recompressed pulse trace shows that a 150-fs pulse duration full width at half maximum was modulated at a beating period of 72 fs. This beating period matches a resonant excitation of plasma wave with an electron density of 2.5 × 10¹⁸ cm^?3, resulting in excitation of a beat wave in hydrogen plasma with wave amplitude of 15 GV/m. The multiple beating oscillations can amplify the plasma wave and improve its structure. This scheme would be ideal for stabilizing the plasma wave strength in the plasma cavity and for realizing a practical laser plasma accelerator.     

Fabricating planar spiral inductances for a wireless charging module by using 355 nm ultraviolet laser ablation

Inductive charging is one of the major wireless charging methods used to induce current through the coil inductances of a receiver. In this study, a 355-nm ultraviolet laser was used to create planar square-spiral inductances (PSSIs) on a copper-coated glass substrate. To obtain the optimal micromachining effect, coils with various line widths (0.5, 1.0, 1.5, and 1.9 mm) were developed on the substrate surface by laser direct writing technique and using a 3-W pulsed laser at various scanning speeds (200, 600, and 1,000 mm/s) and pulse repetition frequencies (60, 80, and 100 kHz). Scanning electron microscopy results revealed that a high pulse repetition frequency and fast scanning speed can reduce the oxidation degree of processed samples. Furthermore, the edge aspect ratio was dependent on the increasing scanning speed, but the increase in the aspect ratio was not substantial. Subsequently, a wireless charging module was used to evaluate the laser ablation quality of the PSSIs, which the induction capacity increased as the oxidation degree of the PSSIs decreased and demonstrated the highest induction capacity of 11.34 % when the scanning speed was 2,000 mm/s. However, because of the power loss during wireless charging and the oxidation degree of the coil surface, the actual inductance value was approximately 15 % of the value estimated using the modified Wheeler formula. In the future, these PSSIs can be applied in wireless charging modules and the results can serve as a reference for enhancing induction capacity in PSSI design.     

远程多光束激光相干场成像拍频误差校正研究

多光束激光相干成像技术是地基观测空间目标的重要方式,各光束的稳定性和性能一致性直接决定着系统成像质量,目前针对系统频率稳定性对成像质量的影响以及激光源频漂的补偿已有一定研究,然而针对多光束发射系统,由驱动放大噪声及声光移频噪声引起的各光束间独立的频漂还需进一步抑制.基于此,本文提出了动态解调和置信区间解调两种抑制方法,理论仿真了动态解调对缓慢频漂抑制的可行性,同时实验证明了置信区间解调法对成像效果的提升,并在200 m和1.2 km的湍流环境中对该解调方法进行了验证.研究表明,置信区间解调法对于各拍频间独立漂移有较好的实时补偿效果,能够有效抑制发射阵列中由声光调制及驱动放大引入的频率噪声,对水平距离1.2 km外的25 mm目标成像角分辨率达到4μrad.本研究为未来远程大功率发射阵列成像中的频率噪声抑制提供了较好的技术方案.     

Acoustooptical system for imaging TV information by using a copper vapor laser

A laser acoustooptical system for projecting TV images onto a large-area screen is developed and produced. A copper-vapor laser with an average power of 20 W is used in it as a radiation source. Images are formed by using green and orange spectral lines. The exposure of a whole TV line on a screen in a time corresponding to the laser pulse duration is the principle governing the operation of the system. A TV line is formed by an acoustooptical modulator (AOM) designed on the basis of a paratellurite (TeO₂) crystal. Frame scanning of an image is performed by using an electromagnetic galvanometer. A high line and frame resolution of about 2000×1000 pixels in the TV standard is obtained. The system makes it possible to form a TV image of size greater than 20 m² with brightness of about 50 cd/m² at a distance of 20 to 100 m. Operating principles of the system and requirements imposed on the laser, the AOM, and other elements are considered.     

Computer analysis of the source image structure in 3D electron-optic systems: II. A stationary electromagnetic system

Computer analysis of the image of an arbitrary (point or extended) source obtained in 3D electron-optic systems is performed. The systems involve magnetostatic and electrostatic fields, which, respectively, focus and deflect the electron beams. Two approaches to image scanning are considered where the scan potentials are applied in two (symmetric and asymmetric) modes. It is shown that the spread function of the source, which characterizes the imaging quality of the system most fully, may serve as a primary computational criterion.     

Cerium oxide nanoparticles protect primary mouse bone marrow stromal cells from apoptosis induced by oxidative stress

The sintering of a silver (Ag) nanoparticle film by laser beam irradiation was studied using a CW DPSS laser. The laser sintering of the Ag nanoparticle thin film gave a transparent conductive film with a thickness of ca. 10 nm, whereas a thin film sintered by conventional heat treatment using an electronic furnace was an insulator because of the formation of isolated silver grains during the slow heating process. The laser sintering of the Ag nanoparticle thin film gave a unique conductive network structure due to the rapid heating and quenching process caused by laser beam scanning. The influences of the laser sintering conditions such as laser scan speed on the conductivity and the transparency were studied. With the increase of scan speed from 0.50 to 5.00 mm/s, the surface resistivity remarkably decreased from 4.45 × 10⁸ to 6.30 Ω/sq. The addition of copper (Cu) nanoparticles to silver thin film was also studied to improve the homogeneity of the film and the conductivity due to the interaction between the oxidized surface of Cu nanoparticle and a glass substrate. By adding 5 wt% Cu nanoparticles to the Ag thin film, the surface resistivity improved to 2.40 Ω/sq.     

High-speed scanning fiber-optic heterodyne interferometer using a micro-electro-mechanical system mirror and an f-theta lens

This paper describes a novel fiber-coupled heterodyne interferometer using a micro-electro-mechanical system (MEMS) mirror and an f-theta lens. In this interferometer system, the cross-polarized laser beams operating at 2 μm with the frequency difference of 100 kHz are introduced by means of the two acousto-optic modulators (AOM). The sample with diameter of 300 mm is uniformly scanned by the 1 mm laser beam with the help of the combined optical scanning configuration, a MEMS mirror and an f-theta lens. The output intermediate signal from the two channels, reference channel and the measurement channel, are processed in the 12 bit analog-to-digital (A/D) process system. Details of our interferometer scheme are discussed.     

All-solid-state continuous-wave laser systems for ionization,cooling and quantum state manipulation of beryllium ions

We describe laser systems for photoionization, Doppler cooling, and quantum state manipulation of beryllium ions. For photoionization of neutral beryllium, we have developed a continuous-wave 235 nm source obtained by two stages of frequency doubling from a diode laser at 940 nm. The system delivers up to 400 mW at 470 nm and 28 mW at 235 nm. For control of the beryllium ion, three laser wavelengths at 313 nm are produced by sum-frequency generation and second-harmonic generation from four infrared fiber lasers. Up to 7.2 W at 626 nm and 1.9 W at 313 nm are obtained using two pump beams at 1051 and 1551 nm. Intensity drifts of around 0.5 % per hour have been measured over 8 h at a 313 nm power of 1 W. These systems have been used to load beryllium ions into a segmented ion trap.     

Reduction in radiation dose with reconstruction technique in the brain perfusion CT

The principal objective of this study was to verify the utility of the reconstruction imaging technique in the brain perfusion computed tomography (PCT) scan by assessing reductions in the radiation dose and analyzing the generated images. The setting used for image acquisition had a detector coverage of 40 mm, a helical thickness of 0.625 mm, a helical shuttle mode scan type and a rotation time of 0.5 s as the image parameters used for the brain PCT scan. Additionally, a phantom experiment and an animal experiment were carried out. In the phantom and animal experiments, noise was measured in the scanning with the tube voltage fixed at 80 kVp (kilovolt peak) and the level of the adaptive statistical iterative reconstruction (ASIR) was changed from 0% to 100% at 10% intervals. The standard deviation of the CT coefficient was measured three times to calculate the mean value. In the phantom and animal experiments, the absorbed dose was measured 10 times under the same conditions as the ones for noise measurement before the mean value was calculated. In the animal experiment, pencil-type and CT-dedicated ionization chambers were inserted into the central portion of pig heads for measurement. In the phantom study, as the level of the ASIR changed from 0% to 100% under identical scanning conditions, the noise value and dose were proportionally reduced. In our animal experiment, the noise value was lowest when the ASIR level was 50%, unlike in the phantom study. The dose was reduced as in the phantom study.     

一种多频局域共振型声子晶体板的低频带隙与减振特性

设计了一种多频局域共振型声子晶体板结构, 该结构由一薄板上附加周期性排列的多个双悬臂梁式子结构而构成. 由于多个双悬臂梁式子结构的低频振动与薄板振动的相互耦合作用, 这种局域共振型板结构可产生多个低频弯曲波带隙(禁带); 带隙频率范围内的板弯曲波会被禁止传播, 利用带隙可以实现对薄板的多个目标频率处低频减振. 本文针对这种局域共振型板结构进行了简化, 并基于平面波展开法建立了其弯曲波带隙计算理论模型; 基于该模型, 结合具体算例进行了带隙特性理论分析. 设计、制备了一种存在两个低频弯曲波带隙的局域共振型板结构样件, 通过激光扫描测振仪测试证实该结构存在两个低频带隙, 在带隙频率范围的板弯曲振动被显著衰减.     

Study on Graphic Distortion in Laser Display

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Study on Graphic Distortion in Laser Display

The mechanism of the graphics distrotion in a laser display system was studied. Based on the mathematical analysis, the pincushion and linear distortions were calculated. Theoretical results agree well with the experimental observation. By tracing laser beams from image plan back to scanners, a relation between the image points on the screen and the scan angles was built. Thus, it has been able to rectify the scanning distortions by computer software effectively.     

Laser direct micromilling of copper-based bioelectrode with surface microstructure array

The laser direct micromilling is proposed to fabricate the microstructure arrays on the surface of dry bioelectrodes using red copper material. Based on the principle of laser machining and SEM results, the forming process of microstructure arrays on the surface of copper-based bioelectrodes is discussed. When the process parameters are varied, the effect of process spacing, laser output power, scanning speed and number of scan on the morphology and geometrical dimension of microstructure array of bioelectrode is investigated. The results show that the cone surface microstructure can be fabricated when process spacing is set to 0.1 mm. Surface roughness of microstructure is greatly changed with different scanning speeds. The height of surface microstructure and recast layer is greatly increased with increasing laser output power. When smaller laser output power or less number of scan are selected, surface microstructure array is difficult to be fabricated. However, it is easy to generate the damage of surface microstructure when the larger output power or excessive scanning times are selected. Moreover, our developed copper-based bioelectrode shows a hydrophobic property when the spacings are selected in the range of 0.1–0.3 mm. Eventually, the optimized process parameters are obtained to fabricate the bioelectrode with cone microstructure array.     

Bit error rate analysis of MISO FSO systems

Abstract

Multiple-input single-output (MISO) systems are employed in free space optical (FSO) links to mitigate the degrading effects of atmospheric turbulence. In this paper, we consider a MISO FSO system with practical transmitter and receiver configuration that consists of radial laser array with Gaussian beams and a Gaussian receiver aperture function. We have employed our previously derived formulation of the power scintillation in which Huygens–Fresnel principle was employed. Therefore, we choose system parameters within the range of validity of the wave structure functions. Using the on-off keying modulation and the log-normal probability distribution function, we quantify the average bit error rate (〈BER〉) of laser array beams in weak turbulence. It is observed that the radial array beams at the transmitter are more advantageous than the single Gaussian beam. However, increasing the number of array beamlets to more than three seems to have negligible effects on 〈BER〉 . It is further observed that 〈BER〉 decreases when the source size, the ring radius and the receiver aperture radius increase.     

Multi-wavelength laser sensor for intruder detection and discrimination

An intruder detection and discrimination sensor with improved optical design is developed using lasers of different wavelengths to demonstrate the concept of discrimination over a distance of 6 m. A distinctive feature of optics is used to provide additional transverse laser beam scanning. The sample objects used to demonstrate the concept of discrimination over a distance of 6 m are leaf, bark, black fabric, PVC, wood and camouflage material. A camouflage material is chosen to illustrate the discrimination capability of the sensor. The sensor utilizes a five-wavelength laser combination module, which sequentially emits identically-polarized laser light beams along one optical path. A cylindrical quasi-optical cavity with improved optical design generates multiple laser light beams for each laser. The intensities of the reflected light beams from the different spots are detected using a high speed area scan image sensor. Object discrimination and detection is based on analyzing the Gaussian profile of reflected light at the different wavelengths. The discrimination between selected objects is accomplished by calculating four different slopes from the objects' reflectance spectra at the wavelengths 473 nm, 532 nm, 635 nm, 670 nm and 785 nm. Furthermore, the camouflage material, which has complex patterns within a single sample, is also detected and discriminated over a 6 m range by scanning the laser beam spots along the transverse direction.     

剪切光束成像技术对纵深目标的成像

剪切光束成像技术是一种能透过大气湍流对远距离目标实现高分辨率成像的主动成像技术.现有相关研究中所采用的目标均为二维平面目标,然而现实中的目标一般都具有三维形貌,目标纵深对回波信号产生的延迟或对成像质量产生不利影响.从剪切光束成像理论出发,在二维目标成像模型的基础上建立了三维纵深目标成像模型,并利用该模型研究了两剪切光与参考光间的频差及目标纵深对成像的影响.仿真结果表明,随着拍频的增大,重构图像质量逐渐下降.剪切光束成像技术可通过减小拍频来提高真实目标成像质量.     

Effects of green laser fluence on the characteristics of graphene nanosheets synthesized by laser ablation method in liquid nitrogen medium

We have studied the effects of laser fluence on the characteristics of graphene nanosheets produced by pulsed laser ablation technique. In this work, The second harmonic of a Q-switched Nd:YAG laser at 532 nm wavelength and 5 Hz repetition rate with different laser fluences in the range of 0.5–1.8 J/cm² was used to irradiate the graphite target in liquid nitrogen medium. The products of ablation were characterized using Fourier transform infrared spectroscopy, field emission scanning electron microscopy, X-ray diffraction pattern, UV–Vis absorption spectroscopy, Raman spectrum and transmission electron microscopy. The Raman spectroscopy indicates that the quality of the graphene nanosheets was decreased while their structure defects were increased as the laser fluence was increased from 0.5 to 1.4 J/cm². Our results suggest that the amount of defects and the number of layers in graphene nanosheets can be changed by adjusting the laser fluence. This study could be a useful guidance for producing of high quality of graphene nanosheets by laser ablation method.     

Mode-locked all-fiber ring laser based on broad bandwidth in-fiber acousto-optic modulator

Active mode-locking of long-cavity all-fiber ring laser based on broad bandwidth in-fiber acousto-optic modulator (AOM) is reported. The proposed AOM combines the advantages of intermodal coupling induced by standing flexural acoustic waves in a double-ended tapered fiber. We focus our attention on the effects of large tapered transitions to improve the bandwidth modulation. Our approach permits the implementation of broad modulation bandwidth (13 nm), high modulation depth (50 %), and low optical loss (1.1 dB) in an 80-μm configuration. The effects of the AOM in the laser performance are also investigated. Transform-limit optical pulses of 25 ps temporal width and 2.7 W peak power were obtained at 2.46 MHz repetition rate.     

Sub-Doppler Two-Photon Laser Spectroscopy of Antiprotonic Helium and the Antiproton-to-Electron Mass Ratio

The ASACUSA collaboration of CERN has recently irradiated antiprotonic helium atoms with two counter-propagating laser beams. This excited some non-linear two-photon transitions of the antiproton at the deep UV wavelengths λ = 139.8–197.0 nm. The counterpropagating geometry of the laser beams reduced the thermal Doppler broadening of the observed resonances. Their narrow spectral lines allowed the measurement of three transition frequencies with fractional precisions of 2.3–5 parts in 10⁹. By comparing the results with three-body QED calculations, the antiproton-to-electron mass ratio was derived as 1836.1526736(23).     

Simple and accurate optical height sensor for wafer inspection systems

An accurate method for measuring the wafer surface height is required for wafer inspection systems to adjust the focus of inspection optics quickly and precisely. A method for projecting a laser spot onto the wafer surface obliquely and for detecting its image displacement using a one-dimensional position-sensitive detector is known, and a variety of methods have been proposed for improving the accuracy by compensating the measurement error due to the surface patterns. We have developed a simple and accurate method in which an image of a reticle with eight slits is projected on the wafer surface and its reflected image is detected using an image sensor. The surface height is calculated by averaging the coordinates of the images of the slits in both the two directions in the captured image. Pattern-related measurement error was reduced by applying the coordinates averaging to the multiple-slit-projection method. Accuracy of better than 0.35 μm was achieved for a patterned wafer at the reference height and ±0.1 mm from the reference height in a simple configuration.