Laser beam deflection by frequency shifting

A new type of beam scanner has been developed which utilizes frequency shifting of a laser beam followed by deflection of the beam in a dispersive element. Theoretical considerations involve the maximization of the frequency shift and number of resolvable spots. An experimental deflector has been constructed which employs a mode-locked 0.633 μm He-Ne laser, lithium-niobate frequency shifter, and a Fabry-Perot dispersion element. Scans of 15 resolvable spots have been obtained with a theoretical access time of 18.5 ns.     

行波偏转器前置短磁聚焦条纹变像管理论设计与实验研究

条纹变像管因其超高时间分辨特性而成为实现皮秒至飞秒量级时间分辨的重要测量仪器.本文设计了一种同时兼顾高时空分辨的行波偏转器前置短磁聚焦条纹变像管.该管型通过减小电子渡越时间以抑制空间电荷效应、采用偏转器前置以及行波偏转方式提高偏转灵敏度,实现整管时空分辨率的大幅提升.利用CST微波工作室有限元法数值计算条纹变像管行波偏转器的通频带宽、偏转灵敏度,结果表明:本设计中的行波偏转器因其较高的通频带宽特性实现了偏转器上的电磁波相速度在很宽频率范围内与电子轴向群速度匹配,产生更有效偏转.利用CST粒子工作室模拟追踪光电子的运行轨迹,通过最佳像面上的时间调制传递函数和空间调制传递函数,计算得到其理论时间分辨率可达220 fs,空间分辨率高于100 lp/mm.同时根据像差定义给出追踪实际电子轨迹的像差计算方法,实现对变像管成像质量评价.最后利用紫外灯对其进行静态测试,获得静态空间分辨率优于35 lp/mm的结果.     

A travelling-wave beam deflector cleave-coupled to a diode laser

A new technique for scanning a diode laser beam is introduced where the beam is deflected in a current-injection-type travelling-wave beam deflector integrated with a diode laser. The deflector, which is formed outside the laser cavity, is cleave-coupled to the cavity. An anti-reflection coating on the deflector output facet suppresses the light returning to the laser. As a result, very smooth deflection of the radiation peak with low background intensity is realized in this device, while retaining high efficiency and low threshold current.     

测量超快现象用光学系统时间特性的研究

超快速电子成象器件的发展,使超快现象的测量成为可能,同时也提出了研究光学透镜系统时间特性的新课题。实验证明:光学系统时间畸变和时间弥散,将影响超快现象的测量。本文除了对皮秒、飞秒变象管扫描相机工作在可见光波段时透镜系统的时间特性进行研究外,还对该系统用于紫外波段时,光学透镜系统的新特点进行了分析。     

全光固体条纹相机的理论及其静态实验研究

全光固体条纹相机采用空间调制抽运光激发平板波导光偏转器,通过精确控制抽运光和信号光之间的时间延迟,实现对入射到波导芯层信号光的偏转扫描.它能有效解决传统变像管条纹相机因空间电荷效应造成的动态范围降低以及光电阴极材料在红外波段探测受限等问题,且结构简单,系统稳定性高,理论时间分辨率可达皮秒甚至亚皮秒量级.本文围绕全光固体条纹相机的核心部件—–AlxGa1-xAs/GaAs/AlxGa1-xAs平板波导光偏转器,研究了在带填充效应、带隙收缩效应以及自由载流子吸收效应作用下GaAs折射率的变化情况;在GaAs折射率变化达到0.01量级,信号光束斑大小和波导宽度之比p=0.5时,得到系统的理论时间分辨率为2 ps;按照静态实验条件求得的理论空间分辨率为17 lp/mm,实验结果显示其值为9 lp/mm.     

Soliton emission at a phase-mismatch boundary in a quadratic nonlinear film waveguide

We report the experimental demonstration of spatial nonlinear beam displacement caused by an interface between periodically modulated and uniform quadratic nonlinearity. We observe intensity- and phase-mismatch-dependent spatial beam displacement at 1548 nm in lithium niobate waveguides. The device has the potential to provide a soliton-emission-based, ultrafast all-optical switch.     

Acousto-Optic Deflector with a High Diffraction Efficiency and Wide Angular Scanning Range

A new acousto-optic deflector with a wide angular scanning range and a high diffraction efficiency has been studied. The device uses an additional deflector, which allows the angle of incidence of the input beam to be adjusted in order to fulfill the Bragg phase–matching condition over the entire scanning range of the main deflector. The characteristics of an anisotropic two-crystal deflector based on paratellurite crystals have been measured. It has been established experimentally that the operating bandwidth of the device is 32 MHz for a diffraction coefficient no less than 90%, which determines a light beam scanning angle of 50 mrad.     

Ultrafast, large-field multiphoton microscopy based on an acousto-optic deflector and a spatial light modulator

We present an ultrafast, large-field multiphoton excitation fluorescence microscope with high lateral and axial resolutions based on a two-dimensional (2-D) acousto-optical deflector (AOD) scanner and spatial light modulator (SLM). When a phase-only SLM is used to shape the near-infrared light from a mode-locked titanium:sapphire laser into a multifocus array including the 0-order beam, a 136 μm × 136 μm field of view is achieved with a 60× objective using a 2-D AOD scanner without any mechanical scan element. The two-photon fluorescence image of a neuronal network that was obtained using this system demonstrates that our microscopy permits observation of dynamic biological events in a large field with high-temporal and -spatial resolution.     

无光栅频率分辨光学开关行迹分析

从无光栅频率分辨光学开关(GRENOUILLE)的测量原理出发,分析了不均匀的光束空间轮廓导致行迹畸变的原因,并通过数值方法模拟了GRENOUILLE内部存在的数据一致性校验机制对这种影响的抑制作用。结果表明:不均匀光束空间轮廓对GRENOUILLE测量结果的影响并不显著;实际测量中更应避免的是使用过小的光束口径,它将导致行迹不完整,从而显著影响时间波形的测量结果。     

无光栅频率分辨光学开关行迹分析

从无光栅频率分辨光学开关(GRENOUILLE)的测量原理出发,分析了不均匀的光束空间轮廓导致行迹畸变的原因,并通过数值方法模拟了GRENOUILLE内部存在的数据一致性校验机制对这种影响的抑制作用。结果表明:不均匀光束空间轮廓对GRENOUILLE测量结果的影响并不显著;实际测量中更应避免的是使用过小的光束口径,它将导致行迹不完整,从而显著影响时间波形的测量结果。     

Simultaneous compensation for spatial and temporal dispersion of acousto-optical deflectors for two-dimensional scanning with a single prism

The dispersive nature of the acousto-optical deflector (AOD) presents a challenge to applications of two sequential orthogonal AODs (a two-dimensional AOD) as XY scanners in multiphoton microscopy. Introducing a prism before the two-dimensional (2D) AOD allows both temporal and spatial dispersion to be compensated for simultaneously. A 90 fs laser pulse was broadened to 572 fs without compensation, and 143 fs with compensation. The ratio of long axis to short axis of the exiting laser beam spot was 3.50 without compensation and 1.14 with compensation. The insertion loss was 37%. Two-photon fluorescence microscopy used the compensated 2D AOD scanner to image a fluorescent microsphere, which improves signal intensity -15-fold compared with the uncompensated scanner.     

超快电子衍射仪理论及实验研究

研制一套同时具有时间分辨及空间分辨能力的超快电子衍射(UED)系统,理论时间分辨能力达到300 fs,空间分辨能力160 lp/mm,并对该系统进行了静态性能分析。实验表明,优化后系统电子束直径约为300 m,电子打靶角度约为0.09,同时对x和y偏转板的灵敏度、电子束斑尺寸及位置稳定性进行定量分析,利用该系统进行多晶铝膜电子衍射实验,分析衍射图样表明系统最小可以分辨单个晶格间距的0.36%。     

超快电子衍射仪理论及实验研究

研制一套同时具有时间分辨及空间分辨能力的超快电子衍射(UED)系统,理论时间分辨能力达到300 fs,空间分辨能力160 lp/mm,并对该系统进行了静态性能分析。实验表明,优化后系统电子束直径约为300 m,电子打靶角度约为0.09,同时对x和y偏转板的灵敏度、电子束斑尺寸及位置稳定性进行定量分析,利用该系统进行多晶铝膜电子衍射实验,分析衍射图样表明系统最小可以分辨单个晶格间距的0.36%。     

Simplified system configuration for real-time Fourier transformation of optical pulses in amplitude and phase

Real-time Fourier transformation (RTFT) of optical waveforms in amplitude and phase (i.e. transform-limited RTFT) is a fundamental operation that enables the realization of many interesting ultrafast signal processing applications, including wavelength-tunable optical pulse filtering, all-optical temporal correlations and convolutions and temporal imaging, among others. In this paper, we demonstrate that under certain conditions, a single time lens (quadratic-phase temporal modulator) followed by a suitable dispersive delay line can be used to implement transform-limited RTFT of optical pulses. The design specifications and constraints of the proposed transform-limited RTFT systems are derived and discussed. As compared with the conventional methods, the proposed design does not require the use of an input dispersive device preceding the time lens or a second time lens after dispersion, thus resulting in a simpler and more practical alternative for implementing TL-RTFT of optical signals. The feasibility of our proposal to operate on picosecond optical waveforms using electro-optic time lenses has been confirmed by numerical simulations.     

超短脉冲Bessel 光束和空间诱导色散效应

 给出了含时的波动方程的一族特解－超短脉冲Bessel光束，其脉冲光束的空间和时间部分可以做分离变量，空间部分在传输过程中保持Bessel光束不变，而时间脉冲部分的传输行为类似于在普通色散介质中的传输，此效应被称之为空间诱导色散效应。     

超短脉冲Bessel 光束和空间诱导色散效应

给出了含时的波动方程的一族特解－超短脉冲Bessel光束,其脉冲光束的空间和时间部分可以做分离变量,空间部分在传输过程中保持Bessel光束不变,而时间脉冲部分的传输行为类似于在普通色散介质中的传输,此效应被称之为空间诱导色散效应。     

基于人眼视觉的直视型微光成像系统MRC模型

首次将最小可分辨对比度(MRC)的概念引入到了直视型微光成像系统。在人眼视觉的基础上,从信号检测的角度出发,推导出了直视型微光成像系统的MRC模型。该模型综合考虑了空间因素和时间因素对成像系统的影响,给出了系统在不同目标照度、不同对比度情况下探测图像时的极限灵敏阈。模拟结果表明,由此得到的直视型微光成像系统的极限分辨率与实际系统给出的分辨率基本一致,是一种能更全面地评价微光成像系统性能的模型。     

Experimental Study on the Spatial Performance of Photorefractive X-ray Semiconductor Ultrafast Response ChipEI北大核心CSCD

The traditional ultrafast electric vacuum devices are usually based on the mechanism of photoelectric conversion, and their performance is restricted by factors such as material response and space-charge effect. It is difficult for the devices like microchannel plate framing cameras, Dilation X-ray Imager (DIXI) , streak cameras to achieve high temporal resolution (100 fs similar to 1 ps) and spatial resolution (similar to mu m) two-dimensional imaging. Ultrafast imaging technology based on photorefractive effect is a new ultrafast diagnostic technology, which has the advantages of high spatiotemporal resolution, all-optical, all and anti radiation. The nonequilibrium carrier lifetime of low temperature grown AlGaAs (LT-AlGaAs) can reach ps-level. The Ultrafast Response Chip (URC) made of LT-AlGaAs has the characteristics of high temporal resolution, meanwhile, good spatial performance is the other key factor for its application. In this paper, the spatial performance of LT-AlGaAs URC is experimentally studied using X-ray, generated by high-energy nanosecond pulsed laser-produced plasma, as the signal. The results show that the URC has the ability of high spatial resolution and large-scale imaging in the X-ray energy dynamic range of 120: 1. The optimal spatial resolution is >= 35 1p/mm (R) MTF = 0.1, and the imaging frame can reach 6.7 mm x 6.7 mm. The results further verify the feasibility of ultrafast diagnostic technology based on photorefractive materials. In the future, LT-AIGaAs URC will be combined with ultrafast framing technologies such as dispersion framing and polarization chirp framing to realize multi-frames and high spatiotemporal resolution two-dimensional imaging.     

空间诱导产生艾里-贝塞尔光弹研究

利用波动方程,研究了脉冲贝塞尔光束在自由空间传输时的空间诱导群速度色散(SIGVD)效应. 结果表明,三阶SIGVD能使脉冲贝塞尔光束的时域逐渐演化为艾里分布. 由于艾里-贝塞尔光弹是一种新奇的时、空都不扩展的局域波包, 能在光与物质相互作用的很多应用领域发挥作用.因此,本文提出了 通过色散管理技术补偿二阶SIGVD,利用三阶SIGVD在自由空间产生艾里-贝塞尔光弹的方案. 为分析这种光弹的时空传输特性,数值模拟了它在色散介质中的传输情况. 结果表明,这种光弹能在色散介质中保持空域不衍射、时域不色散的稳定传输.