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Notes: The magneto-optic response of Pt/Co superlattices is simulated to gain insight into the recent experimental findings of favorable information-storage characteristics. Major trends are reproduced qualitatively, and the calculations indicate that the Pt contributes significantly to the short-wavelength polar Kerr signal (at 4 eV). The influences of the wavelength, angle of incidence, component thicknesses, overcoat, and substrate on the rotation, ellipticity, and reflectivity are evaluated.

Notes: The reflection-transmission problem is considered for light from a boundary between two magnetic media with arbitrary direction of the magnetization within each medium. Explicit formulas are derived for the magneto-optic coefficients.

Notes: The use of circularly polarized radiation is advantageous for the study of magnetic materials using x-ray scattering techniques. The APS is an ideal source of x-ray radiation for such studies. We present a description of the elliptical multipole wiggler (EMW) [S. Yamamoto, H. Kawata, H. Kitamura, and M. Ando, Phys. Rev. Lett. 62, 2672 (1989)] to be constructed at the APS. This device has been chosen for reasons of tunability and special polarization properties. This insertion device is capable of producing circularly polarized x rays on axis. The EMW period will be λu=16 cm, the number of full strength poles in the hybrid structure is 31, and the device length is 2.8 m. The hybrid magnetic structure produces a peak vertical magnetic field with Ky=14 and the electromagnet provides horizontal magnetic field with Kx=1–2. The frequency of the horizontal field change is up to 10 Hz. The beamline will consist of three stations operating in tandem with only one station receiving x rays at any one time. The three stations have three distinct functions, namely Compton scattering, magnetic scattering, and surface scattering. Special considerations will be made to insure the proper control of the polarization when using circular polarized light. The design of the elliptical multipole wiggler beam line will follow an approach very close to that developed by Kawata et al. [Rev. Sci. Instrum. 60, 1885 (1989)]. Our objective is to obtain a high photon flux with energies above 40 keV and well characterized polarization. © 1995 American Institute of Physics.

Notes: A passive end correction scheme used on a prototype undulator is described. This scheme allows the integrated field requirements to be met at all gaps from 11.5 to 200 mm, with no active correction. The main parameters that need to be adjusted are the strength of the end magnets and the height of the next-to-last poles. The first field integral remains constant over the entire gap range, to within 25 G cm in the vertical direction and 50 G cm in the horizontal direction. The second field integral remains constant to within 10 000 G cm2. Results of magnetic measurements are presented. © 1995 American Institute of Physics.

Notes: The first undulator radiation has been extracted from the Advanced Photon Source (APS). The results from the characterization of this radiation are very satisfactory. With the undulator set at a gap of 15.8 mm (K=1.61), harmonics as high as the 17th were observed using a crystal spectrometer. The angular distribution of the third-harmonic radiation was measured, and the source was imaged using a zone plate to determine the particle beam emittance. The horizontal beam emittance was found to be 6.9±1.0 nm-rad, and the vertical emittance coupling was found to be less than 3%. The absolute spectral flux was measured over a wide range of photon energies, and it agrees remarkably well with the theoretical calculations based on the measured undulator magnetic field profile and the measured beam emittance. These results indicate that both the emittance of the electron beam and the undulator magnetic field quality exceed the original specifications. © 1996 American Institute of Physics.

Notes: The magnetic field distribution, gap-dependent steering, and integrated magnetic multipole moments of insertion devices installed in synchrotron radiation sources have stringent requirements for yielding high brightness without adversely perturbing the electron orbit. Correct termination of the ends of the device yields a large number of full-field poles and helps achieve gap-independent steering. End-field tuning methods used for the Advanced Photon Source insertion devices are reviewed. Techniques include magnet strength reduction, reduced height poles, magnetic shims, and pole shaping. Measurements show that two-imensional finite element analysis is a useful tool for predicting general field shape and trajectories. However, experimental entrance steering of different devices with identical end configurations shows variance, necessitating empirical fine tuning of each device. © 1996 American Institute of Physics.

Notes: Today, many bright photon beams in the ultraviolet and x-ray wavelength range are produced by insertion devices installed in specially designed third-generation storage rings. There is the possibility of producing photon beams that are orders of magnitude brighter than presently achieved at synchrotron sources, by using self-amplified spontaneous emission (SASE). At the Advanced Photon Source (APS), the low-energy undulator test line (LEUTL) free-electron laser (FEL) project was built to explore the SASE process in the visible through vacuum ultraviolet wavelength range. While the understanding gained in these experiments will guide future work to extend SASE FELs to shorter wavelengths, the APS FEL itself will become a continuously tunable, bright light source. Measurements of the SASE process to saturation have been made at 530 and 385 nm. A number of quantities were measured to confirm our understanding of the SASE process and to verify that saturation was reached. The intensity of the FEL light was measured versus distance along the FEL, and was found to flatten out at saturation. The statistical variation of the light intensity was found to be wide in the exponential gain region where the intensity is expected to be noisy, and narrower once saturation was reached. Absolute power measurements compare well with GINGER simulations. The FEL light spectrum at different distances along the undulator line was measured with a high-resolution spectrometer, and the many sharp spectral spikes at the beginning of the SASE process coalesce into a single peak at saturation. The energy spread in the electron beam widens markedly after saturation due to the number of electrons that transfer a significant amount of energy to the photon beam. Coherent transition radiation measurements of the electron beam as it strikes a foil provide additional confirmation of the microbunching of the electron beam. The quantities measured confirm that saturation was indeed reached. Details are given in Milton et al., Science 292, 2037 (2001) (also online at www.sciencexpress.org as 10.1126/science. 1059955, 17 May 2001), and Lewellen et al., "Present Status and Recent Results from the APS SASE FEL," to be published in the Proceedings of the 23rd International Free-Electron Laser Conference, Darmstadt, Germany, 20–24 August 2001. © 2002 American Institute of Physics.

Notes: The theoretically predicted prependicular surface anisotropy of ultrathin ferromagnetic Fe films has been confirmed using the magneto-optical Kerr effect. Polar and longitudinal Kerr-effect measurements have been performed in situ on the same fcc Fe/Cu(100) films to study the dependence of the magnetic properties on film thickness and growth temperature conditions. Auxiliary LEED and Auger studies are used to characterize the structure and growth of the films. For films 1.2–5.9 monolayers (ML) thick grown at ∼100 K, for instance, square hysteresis-loop behavior in the polar Kerr effect confirmed the dominance of the perpendicular surface anisotropy. Examples are presented to document how the polar and longitudinal Kerr-effect signals evolve for films thicker than 6 ML due to the easy axis reorienting into the film plane. To differentiate between intrinsic temperature effects and those associated with interfacial compositional changes, the films were thermally cycled and their Kerr signals monitored. Films of thickness around 4 ML retained their characteristic polar Kerr-effect square loops despite thermal cycling between ∼100 and ∼400 K, while those 〈2 ML thick changed irreversibly. These studies confirm that intermixing can be limited to the monolayer range by low-temperature growth conditions, but the LEED results show that the degree of structural ordering of the films is reduced, as expected.

Notes: The surface magneto-optic Kerr effect (SMOKE) is used to explore the magnetism of ultra thin Fe films extending into the monolayer regime. Both bcc α-Fe and fcc γ-Fe single-crystalline, multilayer films are prepared on the bulk-terminated (1×1) structures of Au(100) and Cu(100), respectively. The characterizations of epitaxy and growth mode are performed using low-energy electron diffraction and Auger electron spectroscopy. Monolayer range Fe/Au(100) is ferromagnetic with a lower Curie temperature than bulk α-Fe. The controversial γ-Fe/Cu(100) system exhibits a striking, metastable, surface magnetic phase at temperatures above room temperature, but does not exhibit bulk ferromagnetism.

Notes: Numerical simulations of the Kerr signals from Cu/Co, Pd/Co, and Pt/Co superlattices show, in general, a scaling of the signal with the amount of Co in the superlattice. Experimentally, however, the signal from Pt/Co superlattices at ∼4 eV is larger than that from bulk Co, despite the lesser total amount of Co. This is due to the magnetization induced in the Pt by the Co. Comparison of the Pd/Co and Pt/Co results with experiment indicates that the magnetization induced in the Pt by the Co plays a more important role in the magneto-optic activity than does the induced magnetization of Pd.