Phase effects owing to multilayer coatings in a two-mirror extreme-ultraviolet schwarzschild objective

The aberrations of a multilayer-coated reflective Schwarzschild objective, which are influenced both by mirror surface profiles and by multilayer coatings, are evaluated with a phase-shifting point diffraction interferometer operating in the extreme ultraviolet. Using wave-front measurements at multiple wavelengths near 13.4 nm, we observed chromatic aberrations and wavelength-dependent transmission changes that were due to molybdenum-silicon multilayer coatings. The effects of chromatic vignetting due to limited multilayer reflection passbands on the imaging performance of the Schwarzschild optic are considered. The coating characteristics extracted from the interferometry data on the two-mirror optical system are compared with previously reported coating properties measured on individual mirror substrates.     

Camera for coherent diffractive imaging and holography with a soft-x-ray free-electron laser

We describe a camera to record coherent scattering patterns with a soft-x-ray free-electron laser (FEL). The camera consists of a laterally graded multilayer mirror, which reflects the diffraction pattern onto a CCD detector. The mirror acts as a bandpass filter for both the wavelength and the angle, which isolates the desired scattering pattern from nonsample scattering or incoherent emission from the sample. The mirror also solves the particular problem of the extreme intensity of the FEL pulses, which are focused to greater than 10(14) W/cm2. The strong undiffracted pulse passes through a hole in the mirror and propagates onto a beam dump at a distance behind the instrument rather than interacting with a beam stop placed near the CCD. The camera concept is extendable for the full range of the fundamental wavelength of the free electron laser in Hamburg (FLASH) FEL (i.e., between 6 and 60 nm) and into the water window. We have fabricated and tested various multilayer mirrors for wavelengths of 32, 16, 13.5, and 4.5 nm. At the shorter wavelengths mirror roughness must be minimized to reduce scattering from the mirror. We have recorded over 30,000 diffraction patterns at the FLASH FEL with no observable mirror damage or degradation of performance.     

Atomic force microscopy characterization of Zerodur mirror substrates for the extreme ultraviolet telescopes aboard NASA's Solar Dynamics Observatory

The high-spatial frequency roughness of a mirror operating at extreme ultraviolet (EUV) wavelengths is crucial for the reflective performance and is subject to very stringent specifications. To understand and predict mirror performance, precision metrology is required for measuring the surface roughness. Zerodur mirror substrates made by two different polishing vendors for a suite of EUV telescopes for solar physics were characterized by atomic force microscopy (AFM). The AFM measurements revealed features in the topography of each substrate that are associated with specific polishing techniques. Theoretical predictions of the mirror performance based on the AFM-measured high-spatial-frequency roughness are in good agreement with EUV reflectance measurements of the mirrors after multilayer coating.     

Nanopatterning with interferometric lithography using a compact /spl lambda/=46.9-nm laser

We report the imprinting of nanometer-scale gratings by interferometric lithography at /spl lambda/=46.9 nm using an Ne-like Ar capillary discharge laser. Gratings with periods as small as 55 nm were imprinted on poly-methyl methacrylate using a Lloyd's mirror interferometer. This first demonstration of nanopatterning using an extreme ultraviolet (EUV) laser illustrates the potential of compact EUV lasers in nanotechnology applications.     

Space-resolving flat-field extreme ultraviolet spectrograph system and its aberration analysis with wave-front aberration

The Nam aberration of a flat-field extreme ultraviolet spectrograph system, composed of a varied line-spacing concave grating and a toroidal mirror, was analyzed by calculating the wave-front aberration with respect to an astigmatic reference surface. The toroidal mirror was used to compensate for the astigmatism that was due to the grazing incidence of light at the concave grating. The spectrograph system could form a space-resolved spectrum along the sagittal direction. The spectral and spatial resolutions of the spectrograph system were estimated from the root-mean-square spot size. The actual spectral resolution of the spectrograph system was measured from extreme ultraviolet spectra obtained from plasmas produced by an iodine laser having an energy of 0.5 J in a 4-ns duration, and it was compared with the calculated value.     

Efficiency of linear-to-circular polarization conversion for light reflection at the principal angle by a dielectric-conductor interface

The efficiency eta(LC) of linear-to-circular polarization conversion when light is reflected at a dielectric-conductor interface is determined as a function of the principal angle phi and principal azimuth psi . Constant-eta(LC) contours are presented in the phi , psi plane for values of eta(LC) from 0.5 to 1.0 in steps of 0.05, and the corresponding contours in the complex plane of the relative dielectric function are also determined. As specific examples, efficiencies > or = 88% are obtained for light reflection by a Ag mirror in the visible and near-IR (400-1200 nm) spectral range, and > or =40% for the reflection of extreme ultraviolet (EUV) and soft x-ray radiation by a SiC mirror in the 60-120 nm wavelength range.     

Recording high-dispersion spherical holographic gratings in a modified Rowland mounting by use of a multimode deformable mirror

To reduce the uncorrected higher-order aberrations for holographic gratings requiring an extreme dispersion, we have modified the Rowland mounting by moving the recording laser sources away from the grating. Then, with a multimode deformable plane mirror to record the grating, the correction of all the aberrations up to the fourth order inclusive is found sufficient to obtain a high-quality image. Applied to the FUSE-LYMAN grating, with a groove density of as much as 5740 grooves/mm, for which a resolution of 30,000 was required, this new recording device produces a resolution from 139,000 to 222,000 over the spectral range.     

Broadband Tuning of a Continuous-Wave, Doubly Resonant, Lithium Triborate Optical Parametric Oscillator from 791 to 1620 nm

We report the use of extreme broadband, high reflectivity >99.5%, optical parametric oscillator (OPO) cavity mirrors. A continuous-wave, doubly resonant, OPO demonstrated tuning over a range of 791-1620 nm with a single mirror set. Wavelength tuning was performed by temperature tuning the nonlinear material of lithium triborate. Narrow linewidth oscillation was confirmed throughout the tuning range, and threshold pump power increased gradually from 50 mW near the degeneracy to 800 mW at the tuning band edge in a double-pass pumping configuration.     

Generation of Bessel beams using a magnetic liquid deformable mirror

A deformable mirror made of a magnetic liquid has been used to produce conical surfaces with subwavelength (λ/4) accuracy. The surface profile of the liquid mirror is controlled by 91 small magnetic coils. The mirror exhibits a linear response with respect to the currents driving the coils, and it allows for real-time changes of its surface profile. The magnetic liquid deformable mirror has been used to produce reflected beams having a conical wavefront; the propagation of the reflected beams was verified to be consistent with that of Bessel beams in the near and far field. The large dynamic range of such a deformable mirror has made it possible to generate Bessel beams with a broad range of beam parameters.     

Generation of a flat-top laser beam for gravitational wave detectors by means of a nonspherical Fabry-Perot resonator

We have tested a new kind of Fabry-Perot long-baseline optical resonator proposed to reduce the thermal noise sensitivity of gravitational wave interferometric detectors--the "mesa beam" cavity--whose flat top beam shape is achieved by means of an aspherical end mirror. We present the fundamental mode intensity pattern for this cavity and its distortion due to surface imperfections and tilt misalignments, and contrast the higher order mode patterns to the Gauss-Laguerre modes of a spherical mirror cavity. We discuss the effects of mirror tilts on cavity alignment and locking and present measurements of the mesa beam tilt sensitivity.     

Analysis of imaging properties of a vibrating thin flat mirror

Thin flat mirrors are often used in designing various optical measurement systems. Such mirrors are generally deformed by environmental conditions during measurements. A detailed theory of deformation of a thin flat mirror that oscillates harmonically in the direction of the normal to its surface is introduced in our work. The mirror is treated as a vibrating membrane, and the time-dependent effect of the mirror deformation on the properties of reflected light is studied. A relation is derived for a dynamic wave aberration. On the basis of this relation, calculation of the Strehl definition of the deformed mirror is performed both by exact integration and by approximation. The results obtained can be used for analysis of the influence of mechanical vibrations on the accuracy of optical measurement systems in various practical applications where thin flat mirrors are used.     

Performance of high-density cast silicon carbide in the extreme ultraviolet

The normal-incidence reflectance of high-density cast silicon carbide (SiC) is evaluated in the extreme ultraviolet (EUV) spectral region. High reflectivity in the EUV is achieved. High reflectivity and the relatively low-cost manufacturing process make high-density cast SiC a promising mirror material for EUV applications.     

Fast scanning method for one-dimensional surface profile measurement by detecting angular deflection of a laser beam

A fast scanning method for one-dimensional surface profile measurement is proposed. The profile is measured by integration of a slope distribution of the surface obtained from angular deflection of a scanning laser beam. A scanning optical system that consists principally of a spherical concave mirror and a rotating scanner mirror has reasonably low cost and is insensitive to mechanical vibration because of its high-speed scanning, of the order of milliseconds. A surface profile of a polygonal mirror along a 5-mm width was measured with the scanning method and with an interferometer. The root-mean-square difference between the two measured results is 0.98 nm.     

Design of a high-throughput grazing-incidence flat-field spectrometer

The optical design of a high-throughput grazing-incidence flat-field spectrometer is presented. The spectral focal curve is almost a straight line because of the flat-field focusing properties of spherical variable-line-spaced gratings. The angular acceptance in the direction perpendicular to the plane of dispersion is maximized by means of a focusing spherical mirror mounted with its tangential plane coincident with the sagittal plane of the grating. Analytical calculations for the determination of the optimum mirror parameters are presented. A spectrometer for high-throughput experiments in the 800-60-eV region is designed with an extreme-ultraviolet-enhanced CCD detector: when the available flux is compared with that of a spectrometer with the same kinds of grating and detector but without a focusing mirror, the increase is as much as a factor 3.     

Fabrication of compact turning mirrors in silicon-on-insulator materials

A turning mirror is a key component in compact optical waveguide devices and high-density integrated optics. An improved two-step method for fabrication of high-quality, compact turning mirrors in silicon-on-insulator materials is proposed. First, inductively coupled plasma etching is applied to produce the turning mirror, which keeps the turning mirror compact; then silicon wet anisotropic etching is applied to enhance the quality of the turning mirror by of its polishing surface, correcting its orientation, and improving the verticality. The shape of the turning mirror fabricated by the two-step method is hexagonal or octagonal, matching the optical field of the rib waveguide well. A large effective mirror size to reflect light waves and reduced shrinkage of the mirror size during etching guarantee that a mirror produced by this two-step method will be more compact than previously designed mirrors.     

Open-loop control of a MEMS deformable mirror for large-amplitude wavefront control

A method is introduced for predicting control voltages that will generate a prescribed surface shape on a MEMS deformable mirror. The algorithm is based upon an analytical elastic model of the mirror membrane and an empirical electromechanical model of its actuators. It is computationally simple and inherently fast. Shapes at the limit of achievable mirror spatial frequencies with up to 1.5 microm amplitudes have been achieved with less than 15 nm rms error.     

FEL beam characterization from measurements of the Wigner distribution function

The Free-Electron-Laser FLASH at DESY has been characterized by a quantitative determination of the Wigner distribution function. The setup, comprising an ellipsodial mirror and a moveable extreme UV sensitive CCD detector, enables the mapping of two-dimensional phase spaces corresponding to the horizontal and vertical coordinate axes, respectively. For separable beams this yields the entire Wigner distribution, offering comprehensive information about spatial coherence properties, wavefront, beam profiles, as well as beam propagation parameters.     

Fiber ring laser with a feedback mirror

We describe the spectral and power features of a ytterbium-doped double-clad photonic crystal fiber laser that is operated in a ring configuration with an external mirror that feeds back only one of its two output beams. We compare the operation of the laser with and without an external feedback mirror. We find that the feedback mirror reduces significantly the spectral and power fluctuations. It is also responsible for an interesting spectral phenomenon: The laser frequency is drifting periodically over 9 nm at a rate of 2 nm/s from a short wavelength to a longer wavelength and vice versa.     

空间望远镜层合材料镜片展开过程非线性动力学行为分析

为了研究空间望远镜柔性子镜展开过程对镜片型面精度和望远镜系统的扰动问题,以花瓣式可展开空间望远镜抛物层合镜片为研究对象,基于绝对节点坐标法,采用考虑初始形态曲率的曲壳单元对镜片的形变位移进行描述,表征了层合镜片几何非线性关系与材料非线性关系下的应变和应力关系。利用虚功原理推导了傍瓣子镜展开过程的耦合动力学方程,考虑了镜片弹性变形与大范围运动的耦合作用。针对使用的曲壳单元和传统建模方式,分别对镜片展开过程进行仿真分析,结果表明使用绝对节点坐标法更有利于描述柔性体大变形与大范围运动的耦合,壳单元在描述曲壳结构时更加精确。铰链驱动力矩能够激发镜片的振荡,特别是在多镜片同时展开时,多柔体的耦合作用会严重影响镜面的型面精度,进而扰动卫星本体的姿态。结论对空间望远镜的镜面精度和姿态精度的分析与控制具有理论价值和工程实际意义。     

Illumination system design for a three-aspherical-mirror projection camera for extreme-ultraviolet lithography

A scanning critical illumination system is designed to couple a synchrotron radiation source to a three-aspherical-mirror imaging system for extreme ultraviolet lithography. A static illumination area of H x V = 8 mm x 3 mm (where H is horizontal and V is vertical) can be obtained. Uniform intensity distribution and a large ring field of H x V = 150 mm x 3 mm can be achieved by scanning of the mirror of the condenser. The coherence factor (varsigma) of this illumination system is ~0.6, with the same beam divergence in both the horizontal and the vertical directions. We describe the performance of the imaging optics at varsigma = 0.6 to confirm that the illumination optics can meet the requirements for three-aspherical-mirror imaging optics with a feature size of 0.06 mum.