Design and measurement of a Cu L-edge x-ray filter for free electron laser pumped x-ray laser experiments

An inner-shell photoionized x-ray laser pumped by the Linac Coherent Light Source (LCLS) free electron laser has been proposed recently. The measurement of the on-axis 849 eV Ne?Kα laser and protection of the x-ray spectrometer from damage require attenuation of the 1 keV LCLS beam. An Al/Cu foil combination is well suited, serving as a low energy bandpass filter below the Cu L-edge at 933 eV. A high resolution grating spectrometer is used to measure the transmission of a candidate filter with an intense laser-produced x-ray backlighter developed at the Lawrence Livermore National Laboratory Jupiter Laser Facility Janus. The methodology and discussion of the observed fine structure above the Cu L-edge will be presented.     

Single-shot beam-position monitor for x-ray free electron laser

We have developed an x-ray beam-position monitor for detecting the radiation properties of an x-ray free electron laser (FEL). It is composed of four PIN photodiodes that detect backscattered x-rays from a semitransparent diamond film placed in the beam path. The signal intensities from the photodiodes are used to compute the beam intensity and position. A proof-of-principle experiment at a synchrotron light source revealed that the error in the beam position is reduced to below 7 μm by using a nanocrystal diamond film prepared by plasma-enhanced chemical vapor deposition. Owing to high dose tolerance and transparency of the diamond film, the monitor is suitable for routine diagnostics of extremely intense x-ray pulses from the FEL.     

Reflection of attosecond x-ray free electron laser pulses

In order to utilize hard x-ray free electron lasers (XFEL's) when they are extended to attosecond pulse lengths, it is necessary to choose optical elements with minimal response time. Specular grazing-incidence optics made of low-Z materials are popular candidates for reflectors since they are likely to withstand x-ray damage and provide sufficiently large reflectivities. Using linear-optics reflection theory, we calculated the transient reflectivity of a delta-function electric pulse from a homogenous semi-infinite medium as a function of angle of incidence for s- and p-polarized light. We specifically considered the pulse response of beryllium, diamond, silicon carbide, and silicon, all of which are of relevance to the XFEL's that are currently being built. We found that the media emit energy in a damped oscillatory way, and that the impulse-response times are shorter than 0.3 fs for normal incidence. For grazing incidence, the impulse-response time is substantially shorter, making grazing-incidence mirrors a good choice for deep subfemtosecond reflective optics.     

Quantitative measurement of hard x-ray spectra for high intensity laser produced plasma

X-ray line spectra ranging from 17 to 77 keV were quantitatively measured with a Laue spectrometer, composed of a cylindrically curved crystal and a detector. Either a visible CCD detector coupled with a CsI phosphor screen or an imaging plate can be chosen, depending on the signal intensities and exposure times. The absolute sensitivity of the spectrometer system was calibrated using pre-characterized laser-produced x-ray sources and radioisotopes. The integrated reflectivity for the crystal is in good agreement with predictions by an open code for x-ray diffraction. The energy transfer efficiency from incident laser beams to hot electrons, as the energy transfer agency for specific x-ray line emissions, is derived as a consequence of this work.     

Diffractive elements for a free electron laser

The limits of applicability of geometrical optical methods of calculating diffractive optical elements for terahertz radiation are determined. Use of the method of hot pressing in vacuum chambers to produce polymer transmissive diffractive elements for controlling terahertz radiation is considered. The effect of radiation absorption on the focal spot size and the radiation resistance of the elements are estimated. Experimental study of the optical characteristics of diffraction lenses fabricated in polypropylene revealed 17 percent differences from the diffraction limit.     

A new laser measurement system for precision metrology

Laser measurement systems, based on optical heterodyne interferometry, have been a valuable tool for precision metrology for almost two decades. During this period measurement requirements have steadily increased without an accompanying improvement in system capabilities. This paper describes a new laser head, electronics and interferometers that satisfy present needs and have the attributes to meet future requirements.     

A laser-based machine vision measurement system for laser forming

Laser forming continues to be a promising technology in manufacturing due to its fast speed, flexibility, and low-cost. Measurement of deformation after laser forming is widely needed to verify its convergence to the intended shape in academic research. With the development of laser forming, high requirements on the measurement of the deformed work-piece have been sought such as a 3D profile of the deformed surface, a large measuring range, and measuring convenience. In this paper, a laser-based machine vision measurement system was developed to measure the 3D profile of deformed surface by a one-off scanning process. Based on the 3D profile data, the vertical displacement of the deformed plate was calculated for bending analysis. In addition, as one of the important feature parameters, transverse shrinkage was automatically determined through a novel image-based method during the scanning process. A measuring accuracy of 0.03 mm for vertical displacement measurement and 0.0125 mm for transverse shrinkage were achieved in the developed measurement system. This measurement performance is acceptable in most of the laser forming processes currently studied.     

Asymmetrically cut crystal pair as x-ray magnifier for imaging at high intensity laser facilities

The potential of an x-ray magnifier prepared from a pair of asymmetrically cut crystals is studied to explore high energy x-ray imaging capabilities at high intensity laser facilities. OMEGA-EP and NIF when irradiating mid and high Z targets can be a source of high-energy x-rays whose production mechanisms and use as backlighters are a subject of active research. This paper studies the properties and potential of existing asymmetric cut crystal pairs from the National Institute of Standards and Technology (NIST) built in a new enclosure for imaging x-ray sources. The technique of the x-ray magnifier has been described previously. This new approach is aimed to find a design that could be used at laser facilities by magnifying the x-ray source into a screen far away from the target chamber center, with fixed magnification defined by the crystals' lattice spacing and the asymmetry angles. The magnified image is monochromatic and the imaging wavelength is set by crystal asymmetry and incidence angles. First laboratory results are presented and discussed.     

硬质合金微型钻头激光自动测量系统的研究

针对微型钻头生产批量大、被测尺寸小、测量精度高的特点,研究出一套激光自动测量系统。该系统包括激光测量、CPU数据处理、PLC控制3大部分。系统的主要特点是采用激光信号转换的脉冲宽度比值法进行测量,有效地消除了测量仪器、环境变化等因素对测量精度的影响。     

电子束泵浦准分子激光放大器的双程光路自动准直

提出了一种电子束泵浦准分子激光放大器的双程光路准直方法,以保证光束在放大器中按照预定方向传输,并使多路光束稳定精确地照射靶面.首先,鉴于准分子放大器中无天然准直基准提出了利用双叉丝像传递光路进行准直的方法,即把输入光束叉丝基准作为“近场点”,把输出光束叉丝基准作为“远场点”,并设计了放大器准直光路,编写了相应的软件.然后,在现有实验室条件下开展了电子束泵浦准分子激光放大器双程光路的自动准直实验.最后,分析了影响该方法的相关因素及准直精度.实验及分析表明,设计的准直系统在较短时间内实现了预定传输光路的自动准直,系统自身精度为0.63μrad,光束最大复位误差为13.75 μm,满足了电子束泵浦准分子激光放大器双程光路自动准直的要求.     

A measurement system for complex optical investigations of erosion laser jets

A measurement system for implementing a technique of high spatiotemporal and spectral resolutions is proposed for complex investigations of processes of the formation and evolution of laser-induced bunches under normal atmospheric conditions. Such optical techniques for studying laser-induced metal plasma as laser probing and spectral analysis are used in the diagnostics of plasma parameters. The use of this system made it possible to obtain original data on laser erosion of metals exposed to nanosecond pulses.     

膏布药层厚度在线测量系统的应用研究

介绍了一种基于激光透射法的膏布药层厚度在线测量系统。对系统的测量原理、系统的结构框架、相应的硬件系统及软件系统都做了详尽的阐述。最后给出了测量结果分析,在线测量误差不超过0.1g,证明了该系统的可靠性和可行性,该系统的应用前景比较广阔。     

A four-segment photodiode cantilever-bending sensor for an atomic-force microscope

An electronic circuit for processing signals from a multisegment photodiode (PD) cantilever-bending sensor for an atomic-force microscope (AFM) of “classical” design is described. The electronics includes two analog channels for selecting the difference between the photocurrents of two halves of the receiving area, each channel being normalized to the signal of the total illumination of the PD. The use of modern electronic components allowed the extension of the operating frequency band of the conventional-circuit response from ordinary 200–300 kHz to 2–3 MHz, thus suppressing phase distortions in the band from 0 to 1 MHz. Owing to this, for cantilever-vibration frequencies of up to 200 kHz, the voltage at the circuit output can be accepted with a high accuracy as the signal of the instantaneous position of the cantilever tip with respect to the sample surface. It was shown that the output noise level of the proposed electronics is quite low for the reliable observation of the Brownian motion of the cantilever.     

Multipurpose modular experimental station for the DiProI beamline of Fermi@Elettra free electron laser

We present a compact modular apparatus with a flexible design that will be operated at the DiProI beamline of the Fermi@Elettra free electron laser (FEL) for performing static and time-resolved coherent diffraction imaging experiments, taking advantage of the full coherence and variable polarization of the short seeded FEL pulses. The apparatus has been assembled and the potential of the experimental setup is demonstrated by commissioning tests with coherent synchrotron radiation. This multipurpose experimental station will be open to general users after installation at the Fermi@Elettra free electron laser in 2011.     

激光引信方位探测系统中雪崩管自调节驱动电源设计

针对激光引信方位探测系统光学接收机中雪崩光电二级管(APD)工作温度严重影响其电流增益和信噪比的问题,结合APD的工作特性,分析了输出电压自动可调APD驱动电源设计的必要性.通过对高压发生电路建模分析,总结出开关元件导通截止时间与输入输出电压的关系,从而设计了一种以温度传感器和微处理器(MCU)为控制单元的输出电压可自动调节的APD驱动电源.最后对分析与设计进行实验,实验结果表明该设计有效可行,满足激光引信方位探测系统中APD对驱动电源的要求,使其具有高倍的电流增益和大的信噪比,且工作稳定可靠.     

结合激光准直的二维转角动态测量系统

为了克服现有二维转角动态测量方法结构复杂、成本昂贵的缺点,提出了结合激光准直的二维转角动态测量方法。首先,根据二维转角测量的关键问题提出基于激光准直的测量方法,采用准直激光作为测量基准,以远端的位置探测器作为检测器件。接着,设计测量系统和各组成模块,根据测量要求对系统中的关键模块进行设计和优化。然后,具体设计系统中的测量算法,完成测量模型建立。最后,在±2°范围内进行实验测试和分析。实验结果表明:系统可动态测量,稳定性好,测量重复性误差为1μrad,X轴非线性误差为1.8%,Y轴非线性误差为1.7%,动态带载响应频率在±0.01°内优于200Hz,基本满足二维转角测量的高精度、高重复性、高稳定性的要求。     

A tapered undulator experiment at the ELBE far infrared hybrid-resonator oscillator free electron laser

A tapered undulator experiment was carried out at the ELBE far-infrared free electron laser (FEL). The oscillator FEL makes use of a hybrid optical resonator. The main motivation was to see whether the presence of a dispersive medium in the form of a waveguide in the resonator has any effect on the outcome. The FEL saturated power and the wavelength shifts have been measured as a function of both positive as well as negative undulator field amplitude tapering. In contrast to the typical high-gain FELs where positive tapering proves beneficial for the output power we observed an improvement of performance at negative taper. During the same experiments we studied the characteristics of the detuning curves. The width of the curves indicates a maximum small signal gain for zero taper while the output peak power increases with negative taper. The saturated power output, the detuning curve characteristics, and the wavelength shifts agrees with the theoretical predictions. Details of the experiment are presented.     

激光 ICF 聚变靶丸轮廓测量系统标定方法

针对激光惯性约束聚变靶丸轮廓高精度测量系统的溯源标定问题,提出一种基于激光差动共焦测量原理的标定溯源方法。该方法基于激光差动共焦靶丸测量系统轴向响应曲线过零点精确对应测量系统焦点的性质,首先利用激光差动共焦靶丸测量系统测量经中国计量科学研究院计量检定的标准椭圆块的圆度,其次通过比对测量值和标准椭圆块圆度计量值,得出该系统测量传递系数为1.03,最后通过多次检定验证测量的方法,完成系统的高精度标定。实验结果显示,利用标定完成的系统进行激光聚变靶金属球比对测量,其标准差为37 nm,该标定方法的测量重复性为17 nm,其为靶丸表面轮廓的高精度测量奠定了坚实基础。