Design Of Monochromator Research Articles

DuMond diagram mappings for multi asymmetric crystal monochromators

A set of transformation equations is derived to map DuMond diagrams between crystal faces in a multi-crystal system. The equations are constructed from the Bragg equation linearized about some angle and include the effects of refraction and asymmetry of the crystal faces. The equations form the basis of a ray tracing program for x rays to aid in the design of monochromators.

On the diffraction properties of multilayer coated plane gratings

Multilayercoated laminar gratings are examined in the kinematic approximation with refraction corrections to derive the relationships between wavelength and diffraction angle that determine when constructive interference occurs. Two cases are considered: the amplitude grating and the laminar grating. For each Bragg order of the multilayer we find the grating orders to be nearly linearly arrayed about the grating zero order which occurs at the multilayer Bragg angle and energy. Each reflection carries wavelengths given approximately by the multilayer bandwidth, but dispersed according to the grating equation with its central energy deviating approximately linearly in grating order about the Bragg energy. We are also able to demonstrate the extent to which the device behaves as an X-ray prism, maintaining a constant dispersion angle (given by the Bragg equation) for each diffracted energy. For the laminar grating we derive bar-height relationships for constructive and destructive interference at all grating orders and show that they are commensurate so that odd orders are maximized by the same height that cancels zero order. Finally we present a “two-crystal” monochromator design, using a grating and a non-parallel multilayer, which transmits the wavelength of choice parallel to the incoming beam while passing specularly reflected light into a beam stop at an offset angle.

The LBL 55-meter spherical grating monochromator at SSRL

A 55 meter spherical grating monochromator has been completed at the Stanford Synchrotron Radiation Laboratory (SSRL). The monochromator includes a unique capability for water cooled gratings, and is presently operating with a fused silica grating from 180 to 820 eV. A resolution of 60 meV has been achieved at 400 eV, inferred from the linewidths of the nitrogen 1s-π∗ resonance. A photon flux of 4 × 10 10 photon/s has been observed at 440 eV and 40 mA ring current (and with 0.5 eV resolution). It is expected that this flux value will improve by a factor of approximately 10–30 when a full-performance condensing system is installed later this year. The optical and mechanical systems design of the Rowland Circle monochromator with moving entrance and exit slits is reviewed. The details of the laser interferometer encoded wavelength drive, the mounting of the water cooled gratings, and the mechanical design features which improve the stability and accuracy of the system are described. The alignment of the gratings, grating chamber, and slits is discussed.

Ray tracing results for a doubly focusing independent crystal X-ray monochromator

The need to monochromatize and focus X-rays emitted into appreciable horizontal apertures by storage ring sources (bending magnets and wigglers) leads to the design of focusing monochromators. In order to optimize their design, it is important to understand the combined effect of focusing and diffraction of the flux available at the sample. We analyze here the combined effect of focusing and diffraction for a double-crystal monochromator which is being designed for the Superconducting Wiggler beamline (SCOW) on the ADONE storage ring in Frascati. A double-separated crystal system has been chosen; we study the possibility of obtaining focalization in two steps, by dynamically bending the crystals in order to obtain both tangential and sagittal focusing. Non-focusing and semi-focusing systems have also been considered. The calculations have been performed with the ray tracing program SHADOW. We estimate performances for various focusing geometries and consider the effect of anticlastic curvature.

Mono: A program to calculate synchrotron beamline monochromator throughputs

A set of Fortran programs has been developed to calculate the expected throughput of X-ray monochromators with a filtered synchrotron source; it is applicable to bending-magnet and wiggler beamlines. These programs calculate the normalized throughput and filtered synchrotron spectrum passed by multiple-element, flat, nonfocusing monochromator crystals of the Bragg or Laue type as a function of incident beam divergence, energy, and polarization. The reflected and transmitted beam of each crystal is calculated using the dynamical theory of diffraction. Multiple crystal arrangements in the dispersive and nondispersive modes are allowed, as are crystal asymmetry and energy or angle offsets. Filters or windows of arbitrary elemental composition may be used to filter the incident synchrotron beam. This program should be useful to predict the intensities available from many beamline configurations as well as to assist in the design of new monochromator and analyzer systems.

DuMond Diagram Mappings for Multi Asymmetric Crystal Monochromators

A set of transformation equations is derived to map DuMond diagrams between crystal faces in a multi-crystal system. The equations are constructed from the Bragg equation linearized about some angle and include the effects of refraction and asymmetry of the crystal faces. The equations form the basis of a ray tracing program for x rays to aid in the design of monochromators.

Performance analysis of high-power synchrotron x-ray monochromators

Future synchrotron radiation facilities such as the Advanced Photon Source to be constructed at Argonne National Laboratory will produce dedicated and powerful beams ofx-ray radiation instrumental in advanced research in key areas of science, engineering, and medicine. The development of critical beamline optical components such as monochromators is pivotal in the successful utilization of the generated x-ray beam. The high heat load of the beam can severely distort, and thus adversely affect the performance of, such components. In this paper, a five-step numerical procedure to predict the performance of an x-ray monochromator subjected to high-power synchrotron radiation is described. The predicted performance of a model double-crystal monochromator system expressed in terms of its rocking curves satisfactorily presents the experimental results. This procedure can reliably be used in the design, evaluation, and optimization of monochromators and other optical components.

Stigmatic monochromator design using spherical, normally ruled concave diffraction gratings

A new system of mounting design for concave diffraction gratings is described. The rules of the system, as applied to spherical gratings, are derived from published theory.

Performance of the Dragon soft x-ray beamline (invited)

We report on the performance of a newly constructed synchrotron radiation soft x-ray beamline. This beamline, dubbed Dragon, is a spherical version of the cylindrical element monochromator design proposed previously. By measuring the K-edge absorption spectra of condensed nitrogen, it is determined that this monochromator has achieved resolving power 104 at 400-eV photon energy, using its full 15 by 1 mrad angular acceptance. The ideas and advantages contained in the CEM design have also been experimentally confirmed.

Empirical modeling of systematic spectrophotometric errors

AbstractSpectrophotometers, as electro‐mechanical‐optical devices, perform at a finite level of accuracy. This accuracy is limited by such factors as monochromator design, detector linearity, and cost. Generally, both the diagnosis and correction of spectrophotometric errors require a number of calibrated standard reference materials and considerable effort and commitment on the part of the user. A technique using multiple linear regression has been developed, based on the measurement of several suitably chosen standard reference materials, to both diagnose and correct systematic spectrophotometric errors, including photometric zero errors photometric linear and nonlinear scale errors, wavelength linear and nonlinear scale errors, and bandwidth errors. The use of a single chromatic ceramic tile to correct systematic errors improved the colorimetric accuracy of a set of chromatic and neutral tiles by a factor of two for a typical industrial‐oriented spectrophotometer. Greater improvement can be achieved by increasing the number of tiles and performing a separate regression at each measured wavelength., These techniques have been extremely useful in improving inter‐instrument agreement for instruments with similar geometry.

The three-dimensional dynamic DuMond diagram for X-ray diffraction analysis of nearly perfect crystals

A three-dimensional dynamic DuMond diagram has been constructed, in which the three axes represent the wavelength and vertical and horizontal divergences of an X-ray beam. Such a diagram can be used to analyse successive diffraction of multiple crystals. It is simple and clear cut to use this diagram for the analysis and design of crystal collimators, monochromators and spectrometers involving nearly perfect crystals.

Design of a tunable and focusing single crystal monochromator for powerful X-ray sources

A new design of a focusing monochromator is presented which overcomes both the drastic change in energy resolution when a cylindrically bent crystal is tuned to different energies and the thermal problems that arise with intense wiggler sources. A bi-triangular crystal is asymmetrically cut for the lowest desired energy and pressed to a curved cooling plate which corresponds to the focusing radius at the lowest energy. When tuning to a higher energy the most effective asymmetric cut is re-established by a rotation around the scattering vector. This rotation also changes the effective radius of bend and the position of the focal spot. The focal spots lie on approximately a straight line at a convenient angle to the secondary monochromatic beam.

Soft X-ray grating efficiencies: Reciprocity theorem, blaze maximum and isoefficiency curves

In this article data are presented that show the validity of the reciprocity theorem for diffraction by a blazed grating in the soft X-ray region. With this theorem, a simple formula for the calculation of the diffraction efficiency in blaze maximum can intuitively be derived. Calculations with this formula will be compared to experimental data for first and second order diffraction. Isoefficiency curves for these orders can also be drawn from the experimental data. These will be used to discuss the working parameters of some monochromator designs. By combining the advantages of two well-known monochromator concepts, a new design will be proposed that will allow high resolution while it can be optimized for high transmission and good suppression of higher harmonics.

Measurements of the dispersion and resolution of the general double-crystal monochromator

A general double-crystal device, characterized by the fact that one of the plane crystals swivels around the optical axis between the crystals, represents the continuous transition between the plus (1, 1) and minus (1, −1) positions of double-crystal spectrometers. Expression for the dispersion and resolution of this device are given. Measurements of the spectra of Cr K α1 + α2 as functions of the swivel angle ψ were made for various crystal combinations and are in good agreement with these expressions. With finite entrance X-ray beam divergence, the spectral resolution is highest at ψ = π (in the plus position) and drops at smaller swivel angles. These properties are important for the design of double-crystal monochromators.

Design and performance of a UHV compatible soft X-ray double crystal monochromator at the proton factory

The design and performance of an ultrahigh vacuum compatible soft X-ray double crystal monochromator at the Photon Factory in operation is described. This is a compact version of the JUMBO at SSRL with some improved mechanisms. Ge(111), InSb(111), α-quartz (10 10), beryl(10 10 and GGG(211) were tested as monochromatizing elements with regard to the resolution, intensity and radiation damage.

A plane-grating monochromator for 2 eV ≤ hv ≤ 150 eV

Design and performance of a plane-grating monochromator at UVSOR facility are described. Two monochromators of the present design have been constructed and are used for optical and photoelectron spectroscopy of solids.

Effects of optical component surface figure errors on resolving powers of soft X-ray grating monochromators

We derive the general relationships linking the resolving power λ/Δλ to the figuring accuracy of the optical components for any soft X-ray monochromator. The result is anti-intuitive. It is seen that the figuring is more forgiving the more grazing the optic because of the dispersion term. We analyze existing monochromator designs in the light of these arguments.

Features and initial performance tests of the grating/crystal monochromator

A unique grating/crystal monochromator design to cover the 5–2000 eV spectral range has been installed on the National Synchrotron Light Source X-ray ring. Equations for on- and off-blaze grating operation and resolving power as well as the limitations to the double grating mode are discussed. Preliminary results of performance tests of the resolving power, flux, and harmonic content are reported.

Advanced electron optics for vibrational spectroscopy

Requirements for a next generation high resolution electron energy loss spectrometer for probing surface vibrations are proposed based on several specific applications in which the performance of present generadon instruments is marginal or totally inadequate. Prospects of achieving significant improvements are explored and found to be very good for applications which involve studies of impact scattering phenomena. Results of zoom lens ray tracing studies, analysis of electron trajectories and exit plane images in a hemispherical analyzer in relation to multichannel energy detection and studies of electron trajectories near various field terminators are presented. A prototype analyzer / monochromator design is described which will be used to test the model calculations and to extend the applications of EELS to more detailed studies of impact scattering.

Nonstigmatic input optics for toroidal grating monochromators

Ray-tracing computations show that the resolution of the 6 m/160° TGM cannot be significantly improved by relaxing the requirement of stigmatic focusing. The results suggest a promising direction for future monochromator design employing cylindrical rather than toroidal gratings.