Synchrotron X‐ray tests of an L‐shaped laterally graded multilayer mirror for the analyzer system of the ultra‐high‐resolution IXS spectrometer at NSLS‐II

Characterization and testing of an L‐shaped laterally graded multilayer mirror are presented. This mirror is designed as a two‐dimensional collimating optics for the analyzer system of the ultra‐high‐resolution inelastic X‐ray scattering (IXS) spectrometer at National Synchrotron Light Source II (NSLS‐II). The characterization includes point‐to‐point reflectivity measurements, lattice parameter determination and mirror metrology (figure, slope error and roughness). The synchrotron X‐ray test of the mirror was carried out reversely as a focusing device. The results show that the L‐shaped laterally graded multilayer mirror is suitable to be used, with high efficiency, for the analyzer system of the IXS spectrometer at NSLS‐II.     

Preventing carbon contamination of optical devices for X‐rays: the effect of oxygen on photon‐induced dissociation of CO on platinum

Platinum is one of the most common coatings used to optimize mirror reflectivity in soft X‐ray beamlines. Normal operation results in optics contamination by carbon‐based molecules present in the residual vacuum of the beamlines. The reflectivity reduction induced by a carbon layer at the mirror surface is a major problem in synchrotron radiation sources. A time‐dependent photoelectron spectroscopy study of the chemical reactions which take place at the Pt(111) surface under operating conditions is presented. It is shown that the carbon contamination layer growth can be stopped and reversed by low partial pressures of oxygen for optics operated in intense photon beams at liquid‐nitrogen temperature. For mirrors operated at room temperature the carbon contamination observed for equivalent partial pressures of CO is reduced and the effects of oxygen are observed on a long time scale.     

An optimized side‐cooling scheme for a collimation mirror at the SSRF

Here, in order to reduce tangential slope errors along the centreline of a first mirror's surface, a side‐cooling scheme is proposed. The length of the contact area between the mirror and cooling blocks should be smaller than the beam footprint along the mirror. By optimizing the length and the height of the contact area, reduced slope errors can be obtained. Using this scheme the maximum temperature is not located at the centre of the footprint but shifts to both sides, which fundamentally changes the temperature distribution and enhances the cooling effect compared with the traditional method. This paper presents a `design of experiment' analysis for four kinds of cooling schemes. The structure of the mechanical clamps is also described.     

Aberration theory of plane‐symmetric grating systems

Aberration theory of plane‐symmetric optical systems of mirror and grating has been developed based on the wavefront aberration method. A toroidal reference wavefront surface is used to define the wavefront aberration. Based on the ray geometry, the coordinate mapping relationships of the ray between the optical element and the incident and aberrated wavefronts are derived using a polynomial‐fit method; this enables the resultant coefficients of the wavefront and the transverse aberration to be kept to the fourth‐order accuracy of the aperture‐ray coordinates. By setting up the transfer equations of the field and aperture rays, the contribution to wavefront aberrations from each mirror and grating can be added to make the aberration calculation of multi‐element systems feasible. The theory is validated by the analytic formulae of the spot diagram.     

Phase‐space analysis and experimental results for secondary focusing at X‐ray beamlines

Micro‐focusing optical devices at synchrotron beamlines usually have a limited acceptance, but more flux can be intercepted if such optics are used to focus secondary sources created by the primary optics. Flux throughput can be maximized by placing the secondary focusing optics close to or exactly at the secondary source position. However, standard methods of beamline optics analysis, such as the lens equation or matching the mirror surface to an ellipse, work poorly when the source‐to‐optics distance is very short. In this paper the general characteristics of the focusing of beams with Gaussian profiles by a `thin lens' are analysed under the paraxial approximation in phase space, concluding that the focusing of a beam with a short source‐to‐optics distance is distinct from imaging the source; slope errors are successfully included in all the formulas so that they can be used to calculate beamline focusing with good accuracy. A method is also introduced to use the thin‐lens result to analyse the micro‐focusing produced by an elliptically bent trapezoid‐shaped Kirkpatrick–Baez mirror. The results of this analysis are in good agreement with ray‐tracing simulations and are confirmed by the experimental results of the secondary focusing at the 18‐ID Bio‐CAT beamline (at the APS). The result of secondary focusing carried out at 18‐ID using a single‐bounce capillary can also be explained using this phase‐space analysis. A discussion of the secondary focusing results is presented at the end of this paper.     

Performance of a collimating L‐shaped laterally graded multilayer mirror for the IXS analyzer system at NSLS‐II

The L‐shaped laterally graded multilayer mirror is a vital part of the ultrahigh‐energy and momentum‐resolution inelastic X‐ray scattering spectrometer at the National Synchrotron Light Source II. This mirror was designed and implemented as a two‐dimensional collimating optic for the analyzer system. Its performance was characterized using a secondary large‐divergence source at the 30‐ID beamline of the Advanced Photon Source, which yielded an integrated reflectivity of 47% and a collimated beam divergence of 78 µrad with a source size of 10 µm. Numerical simulations of the mirror performance in tandem with the analyzer crystal optics provided details on the acceptance sample volume in forward scattering and defined the technical requirements on the mirror stability and positioning precision. It was shown that the mirror spatial and angular stability must be in the range <8.4 µm and <21.4 µrad, respectively, for reliable operation of the analyzer.     

Controlling X‐ray deformable mirrors during inspection

The X‐ray deformable mirror (XDM) is becoming widely used in the present synchrotron/free‐electron laser facilities because of its flexibility in correcting wavefront errors or modification of the beam size at the sample location. Owing to coupling among the N actuators of an XDM, (N + 1) or (2N + 1) scans are required to learn the response of each actuator one by one. When the mirror has an important number of actuators (N) and the actuator response time including stabilization or the necessary metrology time is long, the learning process can be time consuming. In this work, a fast and accurate method is presented to drive an XDM to a target shape usually with only three or four measurements during inspection. The metrology data are used as feedback to calculate the curvature discrepancy between the current and the target shapes. Three different derivative estimation methods are introduced to calculate the curvature from measured data. The mirror shape is becoming close to the target through iterative compensations. The feasibility of this simple and effective approach is demonstrated by a series of experiments.     

主动光学技术在制造标准大反射镜中的应用

介绍了利用主动光学技术校正大型标准反射镜残余面形误差和重力变形的方法 ,研制了用于施加局部作用力的工具———机械式作动器的结构与性能 ,作用力的测定方法 ;位于不同位置的作用力引起的镜面变形量的测定与分析 ,与镜面最小面形误差对应的作动器作用力控制矩阵的求解等。对一块Φ2 30mm、中心厚 18mm、R880mm、玻璃材料为K 9的标准球面镜进行了面形误差校正实验 ,取得了较明显的校正效果。     

Measurement of static and vibrating microsystems using microscopicTV holography

This paper describes a microscopic TV holographic arrangement to study the static and vibrating microsystems. In the optical setup, the object beam and the reference beam arms are provided with a phase shifting mirror and a bias phase modulation mirror to carry out the measurement of the out-of-plane deformation and the vibration amplitude fields, respectively. A long working distance microscope is used in the setup for magnifying and imaging the objects on to the CCD camera. For static fringe analysis, the system is used in double exposure subtraction mode of operation, while for vibration fringe analysis, it is used in the time average contrast reversal refreshing mode of operation. An improved approach for qualitative analysis of time averaged fringes helps in reducing the number of frames required for analysis. The usefulness of the system is demonstrated by examples of static and vibration measurements for different microobjects.     

A sagittally focusing double‐multilayer monochromator for ultrafast X‐ray imaging applications

The development of a sagittally focusing double‐multilayer monochromator is reported, which produces a spatially extended wide‐bandpass X‐ray beam from an intense synchrotron bending‐magnet source at the Advanced Photon Source, for ultrafast X‐ray radiography and tomography applications. This monochromator consists of two W/B₄C multilayers with a 25 Å period coated on Si single‐crystal substrates. The second multilayer is mounted on a sagittally focusing bender, which can dynamically change the bending radius of the multilayer in order to condense and focus the beam to various points along the beamline. With this new apparatus, it becomes possible to adjust the X‐ray beam size to best match the area detector size and the object size to facilitate more efficient data collection using ultrafast X‐ray radiography and tomography.     

Fiber laser using a microsphere resonator as a feedback element

We show that a glass microsphere resonator can be used as a wavelength-selective mirror in fiber lasers. Due to their high quality factor (Q approximately 10(8)), microsphere resonators possess a narrow reflection bandwidth. This feature enables construction of single-frequency fiber lasers even when the laser cavity is long. Nonlinear effects (such as stimulated Raman lasing) were also observed in our setup at relatively low pump powers.     

Silicon nitride transmission X‐ray mirrors

Transmission X‐ray mirrors have been fabricated from 300–400 nm‐thick low‐stress silicon nitride windows of size 0.6 mm × 85 mm. The windows act as a high‐pass energy filter at grazing incidence in an X‐ray beam for the beam transmitted through the window. The energy cut‐off can be selected by adjusting the incidence angle of the transmission mirror, because the energy cut‐off is a function of the angle of the window with respect to the beam. With the transmission mirror at the target angle of 0.22°, a 0.3 mm × 0.3 mm X‐ray beam was allowed to pass through the mirror with a cut‐off energy of 10 keV at the Cornell High Energy Synchrotron Source. The energy cut‐off can be adjusted from 8 to 12 keV at an angle of 0.26° to 0.18°, respectively. The observed mirror transmittance was above 80% for a 300 nm‐thick film.     

Concept of Small-Angle Diffractometer in Classical Configuration at the Cold Moderator of the IBR-2 Reactor

The possible concepts whereby a time-of-flight small-angle diffractometer optimized for a neutron moderator operating in the cold (at 30 K) and thermal (at 300 K) modes can be implemented at the IBR-2 reactor are studied on the basis of numerical calculations. Under cold conditions, the peak of the neutronbeam energy spectrum is shifted toward low energies (long wavelengths). This extends the sensitivity range of the instrument with respect to the sizes of the objects under study (1–100 nm and higher). A classical scheme enabling the separation of thermal/cold neutrons (E ~10^–3–10^–2 eV) from the background (formed mainly by fast neutrons), which is based on bent neutron-optical devices, is discussed. Due to restrictions imposed by the geometry of the beamline within which the instrument is planned to be located, a configuration with a short multichannel mirror device for beam bending (beam bender) is preferable. Simulation and optimization of the proposed small-angle instrument is carried out taking into account the real beamline geometry and the available space in the experimental reactor hall. A comparison of the setup has been made with the facility based on the curved neutron guide and the facility with direct view of the moderator.     

微加工薄膜变形镜本征模分析

 介绍了变形镜本征模的构造过程及其特点，分析了从荷兰OKO公司购买的37单元微加工薄膜变形镜的本征模，并用前65阶Zernike多项式分析微加工薄膜变形镜的37阶本征模的特性。搭建了以微加工薄膜变形镜作为波前校正器、变形镜本征模为波前复原控制算法以及高分辨率Shack-Hartmann波前传感器为波前探测器的自适应光学实验系统。实验结果表明：变形镜本征模可以实现模式筛选，也可作为自适应光学系统的波前复原算法。     

Collimating Montel mirror as part of a multi‐crystal analyzer system for resonant inelastic X‐ray scattering

Advances in resonant inelastic X‐ray scattering (RIXS) have come in lockstep with improvements in energy resolution. Currently, the best energy resolution at the Ir L₃‐edge stands at ～25 meV, which is achieved using a diced Si(844) spherical crystal analyzer. However, spherical analyzers are limited by their intrinsic reflection width. A novel analyzer system using multiple flat crystals provides a promising way to overcome this limitation. For the present design, an energy resolution at or below 10 meV was selected. Recognizing that the angular acceptance of flat crystals is severely limited, a collimating element is essential to achieve the necessary solid‐angle acceptance. For this purpose, a laterally graded, parabolic, multilayer Montel mirror was designed for use at the Ir L₃‐absorption edge. It provides an acceptance larger than 10 mrad, collimating the reflected X‐ray beam to smaller than 100 µrad, in both vertical and horizontal directions. The performance of this mirror was studied at beamline 27‐ID at the Advanced Photon Source. X‐rays from a diamond (111) monochromator illuminated a scattering source of diameter 5 µm, generating an incident beam on the mirror with a well determined divergence of 40 mrad. A flat Si(111) crystal after the mirror served as the divergence analyzer. From X‐ray measurements, ray‐tracing simulations and optical metrology results, it was established that the Montel mirror satisfied the specifications of angular acceptance and collimation quality necessary for a high‐resolution RIXS multi‐crystal analyzer system.     

Doppler optomechanics of a photonic crystal

A laser beam directed at a mirror attached onto a flexible mount adds friction to its mechanical motion by the Doppler effect. For a normal mirror the efficiency of this radiative Doppler friction is very weak and practically masked by laser shot noise. We find that it can become very efficient using a photonic crystal mirror near its photonic band gaps. As an example, a Bragg mirror used at the long wavelength edge of its band stop can be efficiently optically cooled using the Doppler friction. The opposite effect opens new routes for optical pumping of mechanical systems: a laser pointing at a Bragg mirror and tuned at its short wavelength edge induces amplification of the vibrational excitation of the mirror leading eventually to its self-oscillation. These new effects rely on the strong dependency of a photonic crystal reflectivity on the wavelength.     

Tests and characterization of a laterally graded multilayer Montel mirror

Multilayers are becoming an increasingly important tool in X‐ray optics. The essential parameters to design a pair of laterally graded multilayer mirrors arranged in a Montel‐type configuration for use as an X‐ray collimating device are provided. The results of X‐ray reflectometry tests carried out on the optics in addition to metrology characterization are also shown. Finally, using experimental data and combined with X‐ray tracing simulations it is demonstrated that the mirror meets all stringent specifications as required for a novel ultra‐high‐resolution inelastic X‐ray scattering spectrometer at the Advanced Photon Source.     

Development of a Joule‐class Yb:YAG amplifier and its implementation in a CPA system generating 1 TW pulses

In this paper the development and implementation of a novel amplifier setup as an additional stage for the CPA pump laser of the Petawatt Field Synthesizer, currently developed at the Max‐Planck‐Institute of Quantum Optics, is presented. This amplifier design comprises 20 relay‐imaged passes through the active medium which are arranged in rotational symmetry. As the gain material, an in‐house‐developed Yb:YAG active‐mirror is used. With this setup, stretched 4 ns seed pulses are amplified to output energies exceeding 1 J with repetition rates of up to 2 Hz. Furthermore, a spectral bandwidth of 3.5 nm (FWHM) is maintained during amplification and the compression of the pulses down to their Fourier‐limit of 740 fs is achieved. To the best of our knowledge, this is the first demonstration of 1 TW pulses generated via CPA in diode‐pumped Yb:YAG.     

基于旋转式反射镜的飞行视觉系统设计

在MEMS麦克风贴片工艺中,真空吸嘴吸取MEMS芯片以后需要进行芯片位姿的精确校正。为实现高速高精度贴片功能,提出了一种基于旋转式反射镜的飞行视觉系统,该方案利用齿轮齿条将吸嘴的升降运动转化为反射镜的旋转运动,通过设计齿轮参数,实现反射镜不干涉吸嘴的拾放功能。当反射镜旋转到与水平位置夹角呈45°时,视觉系统可以获得MEMS芯片的静止的清晰图像,CCD相机采集一幅图像后,在贴片头飞行的过程中,控制系统完成MEMS芯片的位置和角度的校正。实验结果表明,该系统可以获取高质量MEMS芯片图像。该系统结构简单紧凑,成像无失真,不限制贴片头的运动轨迹,显著提高了MEMS芯片的贴片质量和贴片效率,可广泛地应用于贴片机系统中。