Beam Compressor Research Articles

Design concepts for a supermirror V-cavity based combined beam polarizer and compressor system for the upgraded neutron time-of-flight spectrometer NEAT

Abstract Here we present several design concepts for polarization of incoming neutrons based on the use of supermirror optical devices for the application in time-of-flight neutron spectroscopy. The polarization systems, designed for the recently upgraded time-of-flight spectrometer NEAT [1], are using the so-called “V-cavity” approach and provide simultaneous polarization and compression of the neutron beam, due to the geometrical conditions imposed by the instrument layout. Two fundamental design concepts have been explored: hybrid one, which polarizes and compresses simultaneously, and combined one, making the polarization and the compression in two sequential steps. The results are supported by both analytical calculations and simulations by VITESS-package software. The polarizer’s design secures high values of both polarization and transmittance of neutron beam intensity, corresponding to recent state-of-the-arts performances. The comparison of various design concepts and their parameters are presented and discussed.

Method of analysis for determining and correcting mirror deformation due to gravity

The Navy Precision Optical Interferometer, located near Flagstaff, Arizona, is a ground-based interferometer that collects, transports, and modulates stellar radiation from up to six primary flat collectors, known as siderostats, through a common vacuum relay system to a combiner. In the combiner, the modulated beams are superimposed, fringes obtained, and data recorded for further analysis to produce precise star positions or stellar details. The current number of observable stellar objects for the astrometric interferometer can increase from 6000 to at least 47,000 with the addition of full-aperture 20-deg down-tilting beam compressors in each optical train. Such an aperture increase, from the current 12.5 to 35 cm, opens the sky to many additional and fainter stars. Engineering analysis of our beam compressor primary mirror shows that the maximum allowable sag, 21 nm, occurs prematurely at 2.8-deg down-tilt angle. Furthermore, at the operational down-tilt angle of 20 deg, the wavefront deformation increases to 155 nm. We present a finite element analysis technique and design modification concept to reduce tilt-induced deformation on the mirror surface. This work is a first pass to determine the feasibility for a mechanical solution path forward. From this analysis, we found that four outwardly applied 17.8-N forces on the rear surface of the mirror could reduce sag from 155 to 32 nm at 20-deg down-tilt angle.

Super-thin Mikaelian’s lens of small index as a beam compressor with an extremely high compression ratio

Based on a focusing Mikaelian's lens with small refraction index (0<n<<1), an optical device is designed as a super-thin optical beam compressor (e.g., thickness = 3λ0) with an extremely high beam compression ratio (more than 19:1). This device can also be used as a beam collimator or a cylindrical-to-plane wave convertor with a much higher transmissivity than a zero-index metamaterial slab. The output beam shows good directionality in both near field and far field. A metamaterial structure is also designed to realize this device and verify its performance with finite element method (FEM).

SPATIAL BEAM COMPRESSION AND EFFECTIVE BEAM INJECTION USING TRIANGULAR GRADIENT INDEX PROFILE PHOTONIC CRYSTALS

Spatial beam compression of an electromagnetic wave is one of the fundamental techniques employed in microwaves and optics. As there are many ways to achieve this task using the combination of prisms and lenses, recent research suggests the parabolic gradient index photonic crystals (GRIN PC) for the design of spatial beam compressor owing to its functionalities. However, the fabrication of a graded media with the parabolic proflle is a di-cult challenge in practical realization. As an alternative, present work attempts this problem with respect to the triangular gradient index proflle. The performance and aspects of the beam compression are investigated experimentally using the pillar type GRIN PC at the microwave length-scales. The utility of the device for an efiective beam injection to the photonic-waveguide component is further demonstrated experimentally.

Impedance-matched three-dimensional beam expander and compressor designs via transformation optics

Based on the coordinate transformation technique, a three-dimensional beam expander/compressor design is presented. Spatial coordinates in two orthogonal directions tangential to the device boundary are scaled at the same rate. The reflection and transmission coefficients are obtained in a closed form at the planar boundary for a plane wave illumination at an arbitrary incidence angle. The reflection and transmission characteristics under two-dimensional Gaussian beam illuminations are analyzed by constructing the incident, reflected, and transmitted waves as a superposition of plane wave components via Fourier transform. Numerical examples are provided to demonstrate the small amount of reflection compared with two-dimensional counterparts of the expander/compressor.

Microspectroscopic observation of vibrational linear dichroism using polarization-modulated infrared synchrotron radiation

We report on a polarization modulation apparatus on the infrared microscope of the IRIS beamline at BESSY II for dichroitic measurements with high spatial and temporal resolution. It is comprised of a beam compressor in the Fourier transform infrared spectrometer and a linear polarizer and a photoelastic modulator between the spectrometer and the microscope. We show that the spatial resolution of the instrument on thin films of polypropylene is diffraction-limited (10 × 10 μm 2) in the mid infrared wavelength range. This new instrumentation makes possible polarization-dependent microspectroscopic studies of the vibrational linear dichroism and hence the preferred molecular orientation in a variety of samples, ranging from synthetic polymers, wood fibres to living cells. The high spatial resolution permits mapping of small and heterogeneous sample areas while the time resolution can be exploited to probe dynamic processes such as the response of a sample to mechanical stress.

Extremely simple single-prism ultrashort- pulse compressor

We have designed and demonstrated a very simple and compact ultrashort-pulse compressor using a single prism and a corner-cube. Our design is significantly easier to align and tune compared with previous designs. Angle-tuning the prism wavelength-tunes, and translating the corner cube varies the group-delay dispersion over a wide range. When tuned, the device automatically maintains zero angular dispersion, zero pulse-front tilt, zero spatial chirp, and unity magnification. The device can easily be built so that its output beam remains collinear with the input beam, and when the input beam or pulse compressor moves, the input and output beams remain collinear.

Monolithic two-dimensional beam compressor for hard x-ray beams

Using asymmetric diffraction in grazing incidence or in grazing emergence it is possible to expand or compress an x-ray beam in one dimension. Combining two asymmetric diffractions with non-coplanar planes of diffraction it is possible to obtain two-dimensional beam expansion or compression. This paper reports on a monolithic two-dimensional x-ray beam compressor consisting of two non-coplanar asymmetrically inclined {311} diffractors prepared in one silicon crystal block and tested at Optics beamline BM05 at ESRF, Grenoble. The design of the x-ray beam compressor, the results of beam tracing image simulation, the experimental arrangement used for testing and the properties of the x-ray microbeams formed are presented. For the beam energy of 9.5 keV 10- and 13-times beam compression in two directions was observed. Using a metal grid in the incident beam more than 400 microbeams smaller than 10 µm and separated by less than 5 µm were obtained in the outgoing beam. A gain of up to 100 times in intensity per unit area was obtained in comparison with the x-ray beam magnifier geometry, demonstrating a real two-dimensional beam compression.

White beam x-ray waveguide optics

We report a white beam x-ray waveguide (WG) experiment. A resonant beam coupler x-ray waveguide (RBC) is used simultaneously as a broad bandpass (or multibandpass) monochromator and as a beam compressor. We show that, depending on the geometrical properties of the WG, the exiting beam consists of a defined number of wavelengths which can be shifted by changing the angle of incidence of the white x-ray synchrotron beam. The characteristic far-field pattern is recorded as a function of exit angle and energy. This x-ray optical setup may be used to enhance the intensity of coherent x-ray WG beams since the full energetic acceptance of the WG mode is transmitted.

D039 Recent Developments of Curved Graded Multilayers and Multilayer Monochromator Systems for Application on Point and Line Focus X-ray Sources

Curved graded multilayers have opened up new vistas in the application of such elements in many fields of X-ray analysis. In XRD and XRR such optics are used both on primary and diffracted beam side to simplify sample preparation and alignment and to increase intensities and P/B ratio. Beside the material combination in the multilayer stack the performance of these X-ray optical elements and systems is mainly influenced by the accuracy of the multilayer deposition process and the curvature of the mirrors. Performance tests of advanced focussing and collimating optical elements and systems were carried out in commercial diffractometers to demonstrate the beam characteristics. Collimating monochromator systems like Beam compressor and X-ray pointer are show a tunable divergence and sample illumination in one direction and fill the gap between crossed coupled / side-by-side mirrors and the single collimating mirror. There are further analytical problems, where the characteristics of the desired X-ray optical systems can be tailored to the particular application (sample size, intensity, resolution,..).

Beam Propagation Method for Three-Dimensional Surface Acoustic Waveguides

A beam propagation method (BPM) based on the finite element method (FEM) is newly formulated for the analysis of longitudinally varying three-dimensional (3-D) surface acoustic waveguides. In order to avoid nonphysical reflections from computational window edges, a transparent boundary condition (TBC) for acoustic waves is proposed. To show the validity and usefulness of this approach, numerical results for a Rayleigh-wave beam compressor using Δv/v-type guidance are presented.

Optical collimation and compression of a thermal atomic beam

We have performed an experiment to optically cool and compress a thermal beam of sodium atoms by employing a two-dimensional version of a magneto-optical trap. The beam compressor employs a tapered transverse magnetic field gradient formed by four pairs of permanent magnets. We measure the efficiency of collimation and compression as function of longitudinal velocity group.

On the Design of High Performance Planar Surface Acoustic Wave Convolvers

The design of planar surface acoustic wave convolvers is discussed, specifically with respect to beam compressor, waveguide, and output circuitry. It is shown that wide-band beam compression with a few tenths of a decibel in lossesand low excitation of undesired guide& modes may be implemented by multistrip structures. Further it is demonstrated how metal strip acoustic waveguides can be designed with only a few degrees of phase distortion over a 30 percent relative band- width in convolvers with timebandwidth products exceeding 3000. The convolver output configuration is modeled as a lossy coplanar electromagnetic waveguide, and it is shown how the output circuit should be designed to maintain the required bandwidth with aminimum of circuit losses. Measured data for several convolvers are presented.

Beam profile shaping for laser radars that use detector arrays

The beam shaper we developed shapes the transmit beam of a CO(2) laser radar that uses a linear detector array. It consists of a diffraction grating and an anamorphic prism beam compressor and produces a stretched profile that efficiently and uniformly illuminates the far-field footprint of the detector array. The diffraction grating phase modulates the near field or the laser beam to generate a far-field flattop intensity profile, whereas the compressor produces the necessary profile eccentricity. We have achieved conversion efficiencies in the 70-90% range.

Laser beam profile shaping with binary diffraction gratings

A laser beam shaper has been developed to achieve efficient conversion from a gaussian intensity profile to a flattop intensity profile in far-field or focal-plane domains. This beam shaper consists of a diffraction grating and an anamorphic prism beam compressor. The diffraction grating phase modulates the near field of the laser beam to generate a far-field flattop intensity profile, whereas the compressor produces the necessary profile eccentricity. The position, the relief height, and the relative grating periodicity of the beam shaper can be used to change the shape of the beam profile in a flatness-versus-rolloff tradeoff.

PS Beam Measurements at Flat-Top Fields near Transition Energy

Beams up to 1013 protons were kept circulating for more than 100 ms at various magnet field levels near transition and the beam behaviour was observed for several radial positions. These levels corresponded notably to values of n (= ?-2 - ?tr-2) in the range from 10-2 to < 10-4. They were measured using i) the synchrotron frequency, ii) the change in revolution frequency with radial position, iii) debunching times, and, close to transition, iv) the onset of the negative mass instability. Results from i), ii) and iv) agree well with standard theory and from iii) with a theory taking into account conditions close to ?tr. The negative mass instability was observed even when, due to the spread in n values, only part of the beam was above transition. No losses and no global instabilities were observed down to ? ? 5 . 10-4 (below transition). Experimental data and their explanation are presented and the interest of operating beam compressor rings close to ?tr is pointed out.

Efficient three-wavelength-output SAW multistrip beam compressor for convolver applications

The problem of obtaining very narrow surface acoustic wave beams from multistrip compressors is examined experimentally, and a modified geometry is described which allows an extension of previous design methods to narrower output beam compressors, such as required, for example, for direct feeding of a 3λ-wide acoustic waveguide in a monolithic convolver.

Erratum: Efficient three-wavelength-output SAW multistrip beam compressor for convolver applications

Erratum: Efficient three-wavelength-output SAW multistrip beam compressor for convolver applications

Nonsymmetrical multistrip coupler as a surface-wave beam compressor of large bandwidth

The equations for the performance of a multi strip coupler, in which the two tracks involved are of different geometries and acoustic characteristics, are presented in a convenient form that includes the effects of the strip length between the two tracks. Using this analysis, a beamwidth compressor, in which the trackwidths differ by a factor of ten, has been designed and constructed. Since the energy transfer from one track to the other is complete, the energy density in the acoustic beam is increased by a factor of ten over a very large operating bandwidth.