Charles H. Pruett

6‐m TGM implementation at the Wisconsin Synchrotron Radiation Center (SRC)

We recently commissioned the SRC/Vanderbilt University 6‐m toroidal grating monochromator beamline. The problems with mirror heating, signal normalization, monochromator control, and scattered light reduction have led to several innovations on this line, making for a better user interface and adding to the stability and reliability of the final image. We discuss these innovations, and how they affect the user. They include a built‐in laser alignment system, a sapphire windowed gate valve, entrance mirror temperature stabilization, computer automation and control, a beam‐chopper, and the capability of real‐time monitoring of the photon flux during the experiment. We have used noble gas resonance lines to carefully characterize the wavelength resolution of the beamline as a function of energy over a range of beamline parameters. The results demonstrate that by limiting the horizontal width of the image at the slits, and by masking outer portions of the gratings, the flux/bandwidth ratio can be improved at t...

A VUV 4 m normal incidence monochromator

Abstract A 4 m normal incidence monochromator for use at the Tantalus storage ring is described. A general description of the instrument is given, together with a brief discussion of the optics required to match the angular acceptance of the monochromator to the angular spread of the source. With a 3600 lines mm −1 grating the estimated flux at the blaze wavelength of 304 A with a bandwidth of 0.01 eV and 100 mA of circulating current, is 6 × 10 9 photons s −1 .

Alignment techniques for calibration and installation of a 6-m Toroidal Grating Monochromator

Abstract The University of Wisconsin Synchrotron Radiation Center Optics Group has recently completed the installation of three 6-m Toroidal Grating Monochromator (TGM) beamlines on the Aladdin ring. Two of these beamlines image bending-magnet radiation and the third images radiation from the 30-period undulator on loan to the Synchrotron Radiation Center from the Stanford Synchrotron Radiation Laboratory and Lawrence Berkeley Laboratory. Each beamline required an accurate alignment strategy. This is due to the long source-to-final-image distance and the five independent critical elements: entrance mirror, entrance slit, grating chamber, exit slit, and exit mirror. The TGM grating chamber houses up to six gratings on a revolving carousel which is scanned with a sine-drive. We will describe grating stability checks and adjustments to linearize the grating scan calibration. We will also outline the basic alignment procedures from the source point, through the grating chamber, to the final focus. The procedure we have used provided sufficiently accurate alignment to realize the high throughput and resolution capabilities of the 6-m TGMs. The methods also allow later checks on critical degrees of freedom of the optical components.

New Synchrotron Radiation Center beamlines at Aladdin

In the past year, the Synchrotron Radiation Center (SRC) staff has installed five new beamlines at SRC. Three of these beamlines are ‘‘public’’ beamlines operated by SRC for experiments selected from peer‐reviewed proposals. Fifty to seventy‐five percent of the experimental time on the other two beamlines is managed by the SRC as a consequence of the SRC being a partner in participating research teams (PRTs). These new beamlines bring the number of VUV and soft x‐ray research beamlines installed on Aladdin to 17 as of August 1988. Including two storage ring optical diagnostic ports, there will be 20 ports in use on Aladdin by the end of 1988.

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.

Vibration isolation and damping for long focal length synchrotron radiation instruments

Abstract Vibrations of the optical elements in long focal length, high resolution monochromators and other long focal length optical systems used at synchrotron radiation facilities can lead to serious degradation of the performance of these systems. As higher resolution instruments with state-of-the-art spherical and plane elements come on line, vibration will become an increasingly serious problem. The vibrations excited in beamline elements can be at least as serious as position variations of the synchrotron radiation source. Vibrations of beamline and monochromator components may be driven by acoustic waves, ground motion, scanning system vibrations, or vibrations coupled in from experimental equipment such as pumps, fans, motors, etc. This paper will include a discussion of isolation and damping of vibrations in monochromators and beamlines. Various diagnostic methods are described, and a case study of vibration-caused loss of resolution in a 4 m normal incidence monochromator will be presented.

User operation of the first undulator on Aladdin

The first undulator on Aladdin recently began operating as a user facility. The device is equipped with a 6-meter toroidal grating monochromator beamline. The undulator and its beamline have several unique characteristics. Furthermore, the adjacent bending magnet beamline is almost a twin of the undulator beamline, with similar grating efficiencies and reflection losses. This makes it easy to directly compare undulator and bending magnet source beamlines in a realistic environment. The results indicate that the undulator beamline produces between 20 and 100 times more flux in the first harmonic than a similar beamline on a bending magnet. The excellent polarization of 99.5% for the first harmonic makes this beamline extremely useful for polarization studies. User programs based on the undulator radiation included angle-resolved photoemission in gas phase and tests of optical components. The beamline is now entirely dedicated to soft X-ray spectromicroscopy (project MAXIMUM).

Investigations of resolution degradation due to scattering in a long focal length monochromator

Scattering of light by optical surfaces causes broadening of focused images and can limit the resolution of monochromators and other optical systems. This problem is most troublesome in the vacuum ultraviolet and x‐ray region of the spectrum with long focal length, high resolution instruments. The resolution of a 4‐m normal‐incidence monochromator was found to be limited by scattering due to damaged replica grating surfaces. The effect of scattering on resolution was documented by scanning the zero‐order peak with detectors sensitive to different wavelengths of light. In one case a scan of zero order with a visible sensitive photomultiplier tube gave a linewidth of 0.05 A. The same image scanned with a gold diode detector which is sensitive below 1100 A gave a peak width of 0.39 A. Microscopic examination and knife‐edge bench tests of the gratings provided additional evidence that this problem was caused by scattering. It is suggested that use of image scans at different wavelength could be used as a simp...

Recent instrumentation developments at the university of Wisconsin synchrotron radiation center

Abstract Two new monochromators have been installed at the Wisconsin Synchrotron Radiation Center and four more are being designed and constructed for installation later this year. The new instruments installed are an uhv version of a vertically dispersing Seya-Namioka monochromator and an adjustable slit version of the “Grasshopper” grazing incidence monochromator built at the University of Wisconsin Physical Sciences Laboratory for use at the Stanford Synchrotron Radiation Project The new instruments to be installed later are a 4 normal incidence monochromator designed around a high efficiency Bausch and Lomb grating ruled for the Sky Lab Program and three grazing incidence toroidal grating monochromators designed for use with special Jobin-Yvon holographic gratings. The work on the toroidal grating monochromator is proceeding in collaboration with research groups from the IBM Watson Laboratories and the University of Pennsylvania. Operating characteristics achieved or to be expected with these instruments will be discussed.