Mark Bissen

Ultraviolet/ozone cleaning of carbon-contaminated optics

It is shown that ozone generated by UV light can be used to clean carbon-contaminated synchrotronradiation optics.

Cleaning of optical surfaces with photogenerated reactants

Abstract Cleaning of synchrotron radiation optics with photogenerated reactants has several advantages over discharge cleaning methods. In discharge cleaning, reactive species from the discharge must react with contamination on the surface while the surface is shielded from the harsher elements of the discharge which can contaminate or degrade the surface. In contrast, if reactive species can be generated near the surface by photons, the problem of shielding can be eliminated and in some cases higher cleaning rates can be obtained. Different cleaning methods were evaluated by measuring the rates of removal of polymethylmethacrylate films with a thickness monitor. A number of different light sources and geometries were tested. The highest cleaning rates were observed with atmospheric-pressure UV/ozone cleaning. This method has been extensively investigated for cleaning of hydrocarbon contamination from semiconductor surfaces. Our studies indicate that it is also effective in removing the graphite-like contamination from synchrotron radiation optics. Compared to lower pressure methods it is simple, low cost, faster, and more selective. It does require venting of vacuum chambers; however, in many cases optics can be cleaned without demounting, saving considerable time and effort. This method has been used successfully to clean gratings and mirrors in several beamlines.

First results of SRC’s new high‐energy resolution variable line density grating monochromator beamline: HERMON

A new high‐resolution soft x‐ray beamline utilizing a variable line density grating has been constructed and tested at SRC. In addition to normal grating rotation, the grating housing mechanism allows a translation of the grating. This additional motion of the grating can be used in such a way that grating aberration effects such as defocus, coma, and spherical aberrations are minimized over the entire scan range. In order to achieve the theoretical resolving power of 105–5000 over the photon energy range of 280–1150 eV, extreme care had to be exercised in positioning and controlling the grating scan angle (<0.12 arcsec) and focus drive position (<10 μm). Using a spherical grating with a figure error of <0.2 arcsec and 10 μm slits, we were able to experimentally reproduce our theoretical predicted energy resolution over a wide energy range. We present photoabsorption data of the K‐shell edges and associated Rydberg states of Ne, O2, and CO. The high‐resolution monochromator unveils structures which were p...

Design study of a high resolution soft X-ray monochromator with a movable variable groove density grating

Abstract We discuss the design and optimization of a fixed slit, single element spherical grating monochromator. A novel scheme utilizes the translation and rotation of a grating with a polynomial groove density variation. Optimization of the grating parameters minimizes the major aberration terms and linearizes the total energy resolution over the scan range. With a grating slope error of 0.2 the resolving power ranges from E / Δ E ≥ 10 4 to 5×10 3 over the energy range of 500 to 1100 eV.

Evaluation of a new VUV/soft x‐ray toroidal grating monochromator with a movable exit slit

The performance of a toroidal grating monochromator can be significantly improved by compensating for the wavelength dependent defocusing aberration by means of a movable exit slit. Model calculations of a movable exit slit design show a resolving power that varies nearly linearly with wavelength over the scan range. The energy resolution follows the slope between two optimized resolution minima of a fixed slit TGM. The overall improvement in resolution due to the movable slit depends critically on the figure error of the toroid surface. The Al(LII,III) core edges provide a means to calibrate gratings and determine the resolution at 72.8 eV. A method is described for using the shift in core edge with exit slit position to enable final alignment of the exit slit motion providing stability of energy calibration of 2 meV over the scan range. Comparison of calculations and measured resolution suggests that slope errors remain the limiting factor in performance.

Precision motion and position control for the Plane Grating Monochromator at SRC

A nearly stigmatic Plane Grating Monochromator (PGM) under commissioning for the new undulator beamline at the Synchrotron Radiation Center will provide a resolving power > 10000 as it scans from 8 to 240 eV. Scanning requires the precise, simultaneous rotation of a plane mirror and a combined rotation-translation of a plane grating in close proximity to one another inside a UHV chamber. The required scanning motions are significant due to the large energy range covered by a single grating. The mirror and grating rotate nearly 23 and 33 degrees respectively and the grating translates approximately 200 mm. Sub-arcsec angular resolution allows several steps to be taken across the monochromators energy resolution. Both rotations utilize a combination stepping motor-piezoelectric actuator scan drive that is controlled with a feedback loop using a laser interferometer to measure the in-situ rotation of the optics. The grating mechanism is supported via bellows to an external stepping motor driven stage that travels directly on an inspection grade granite block. The stage position is controlled with a feedback loop using a precision linear encoder. A positional accuracy and vertical stability of a few micrometers is achieved on the grating translation which prevents the image from shifting at the exit slit and introducing energy calibration errors.

A high-resolution variable-line-spacing spherical-grating monochromator with a movable exit slit

A design for a spherical-grating monochromator based on the rotation of a variable-line-spacing grating and a movable exit slit in order to minimize the defocus, coma, and spherical aberrations is discussed. The resolution of the proposed monochromator has been investigated both analytically and by means of ray tracing. With a grating figure error of ± 0.1 arc sec, the resolving power ranges from 104 to 5 × 103 over the energy range 380–1260 eV. The total travel of the exit slit required for scanning this energy range is less than 250 mm.

Implementation of an undulator beamline on Aladdin

Abstract The first undulator monochromator on the Aladdin storage ring has been installed and recently tested. The design and alignment of an undulator beamline presented several unique problems not normally encountered in the design of bending magnet beamlines. The primary problem is the lack of visible radiation from the undulator source when it is operated under normal conditions. In this case a temporary beamline was installed to measure the intensity of undulator light transmitted through a pinhole which could be horizontally and vertically scanned through the undulator beam. This was used to adjust the steering of the beam to be centered in the port and to do some nondispersive characterization of the undulator. This temporary line was designed to permit precision alignment of the components of the beamline according to the measured position of the full energy beam. The monochromator used on this beamline is a 6 m toroidal grating monochromator (TGM). It allows further dispersive testing of the undulator and provides dispersed undulator flux for user experiments. The beamline is identical in terms of expected reflectivity losses and grating efficiencies to two similar beamlines implemented on bending magnets. This allows direct comparison of the flux available to experimenters from undulator sources to flux from bending magnets. Initial measurements indicate that with the undulator gap set for 50 eV, at the peak of the first harmonic, the undulator beamline produces 40 times more flux than a similar beamline using a bending magnet source.

Undulator 4 meter NIM at SRC

A new 4 meter normal incidence monochromator (NIM) has recently been commissioned at the Synchrotron Radiation Center (SRC). The beamline utilizes two indexing spherical gratings to cover the energy range of 6–50 eV. A resolution of 0.35 meV at 15.765eV has been measured, which agrees well with the theoretical value. The source for the beamline is a 3.5 m long, 10.9 cm period electromagnetic undulator. The device can be scanned through the full energy range at any time with beamline based controls.

System for monitoring position of the photon beam in the new undulator beamline at SRC

A system of beam position monitors was developed for the plane grating monochromator (PGM) undulator beamline at the Synchrotron Radiation Center (SRC). Two monitors are located in the upstream section of the beamline providing the capability of measuring the transverse angular and spatial motion of the photon beam. The jaws of the entrance slit of the monochromator may also be used as monitors to detect changes in the vertical position of the source. Overall, the system allows measurements of the photon beam position and angle to be done with ∼10 μm and ∼3 μrad accuracy, respectively. The aperture of the monitors can be changed in both the vertical and horizontal direction. Thus, the beam motion can be measured with the highest possible resolution for any value of the undulator deflection parameter K. In addition, the design of the monitors provides the capability of mapping the angular power distribution of the photon beam. The first monitor was installed and successfully tested. The design of the syste...