E. Gluskin

NANOMETER FOCUSING OF HARD X RAYS BY PHASE ZONE PLATES

Focusing of 8 keV x rays to a spot size of 150 and 90 nm full width at half maximum have been demonstrated at the first- and third-order foci, respectively, of a phase zone plate (PZP). The PZP has a numerical aperture of 1.5 mrad and focusing efficiency of 13% for 8 keV x rays. A flux density gain of 121 000 was obtained at the first-order focus. In this article, the fabrication of the PZP and its experimental characterization are presented and some special applications are discussed.

Development of zone plates with a blazed profile for hard x-ray applications

A linear and a circular zone plate with a blazed zone profile (ZPBP) have been fabricated and characterized using synchrotron x rays. The ZPBPs have significantly improved performances in terms of focusing efficiency and the background near the focus compared to those of a zone plate with a square profile, of which the transmission function can be characterized by a binary square wave. In many respects and practical cases, an x-ray ZPBP may be used in a way analogous to an optical lens in the visible light region. In this article, the experimental characterization of the ZPBPs is presented and some special applications are discussed.

Performance of a high-resolution x-ray microprobe at the Advanced Photon Source

We have developed a x-ray microprobe in the energy region from 6 to 20 keV using undulator radiation and zone-plate optics for microfocusing-based techniques and applications at a beamline at the Advanced Photon Source (APS). The performance of the beamline was shown to meet our design objectives, including preservation of the source brilliance and coherence, selectable transverse coherence length and energy bandwidth, high angular stability, and harmonic suppression of the beam. These objectives were achieved by careful thermal management and use of a novel mirror and crystal monochromator cooling geometry. All beamline optical components are water cooled, and the x-ray beam in the experiment station is stable in beam intensity, energy, and position over many days with no active feedback. Using a double-crystal Si(111) monochromator, we have obtained a focal spot size (FWHM) of 0.15 μm(v)×1.0 μm(h), and a photon flux of 4×109 photons/sec at the focal spot, and thus a photon flux density gain of 15,000. A...

The magnetic and diagnostics systems for the Advanced Photon Source self-amplified spontaneously emitting FEL

A self-amplified spontaneously emitting (SASE) free-electron laser (FEL) for the visible-to-ultraviolet spectral range is under construction at the Advanced Photon Source at Argonne National Laboratory. The amplifier part of the FEL consists of twelve identical 2.7-meter-long sections. Each section includes a 2.4-meter-long, 33-mm-period hybrid undulator, a quadruple lens, and a set of electron beam and radiation diagnostics equipment. The undulatory will operate at a fixed magnetic gap (approx. 9.3 mm) with K=3.1. The electron beam position will be monitored using capacitive beam position monitors, YAG scintillators with imaging optics, and secondary emission detectors. The spatial distribution of the photon beam will be monitored by position sensitive detectors equipped with narrow-band filters. A high-resolution spectrograph will be used to observe the spectral distribution of the FEL radiation.

High-performance multilevel blazed x-ray microscopy Fresnel zone plates: Fabricated using x-ray lithography

Diffractive lenses are becoming the optical elements of choice for many applications. One type of diffractive lens, the binary zone plate, has already demonstrated high‐resolution performance experimentally. However, in order to increase the diffraction efficiency of these zone plates, a blazed grating profile must be used. This can best be approximated by a staircase grating profile, created by multilevel exposures. Using x‐ray lithograph, we fabricated for the first time circular, linear bi‐ and trilevel zone plates, with gold structures 0.75 μm thick (per level), on silicon nitride substrates. The zone plates were designed for use at a wavelength of 1.54 A, and had a theoretical efficiency of 68.5% for bilevel and 81.5% for trilevel zone plates. Due to the large depth of focus and high resolution inherent to x‐ray lithography, the finished zone plate exhibits very steep sidewall profiles, with linewidth resolution down to 0.25 μm. Such vertical sidewalls are essential for achieving high lens efficiency...

Measurements of nonlinear harmonic generation at the Advanced Photon Source's SASE FEL

SASE saturation was recently achieved at the Advanced Photon Sources SASE FEL in the low-energy undulator test line (LEUTL) at 530 nm and 385 nm. The electron beam microbunching becomes more and more prominent until saturation is achieved. This bunching causes nonlinear harmonic emission that extends the usefulness of a SASE system in achieving shorter FEL wavelengths for the same electron beam energy. They have investigated the intensity of the fundamental and second-harmonic undulator radiation as a function of distance along the undulator line and present the experimental results and compare them to numerical simulations. In addition, they have measured the single-shot second harmonic spectra as well as the simultaneous fundamental and second harmonic spectra and present the experimental results.

Fabrication of hard x-ray phase zone plate by x-ray lithography

Fresnel phase zone plates for hard x‐ray microfocusing have been fabricated. An original x‐ray mask written by e‐beam lithography was replicated into thick PMMA by x‐ray proximity printing. The pattern was transferred into gold and nickel by electroplating. A smallest linewidth of 0.25 μm with an aspect ratio of 14 in the metal pattern has been achieved. Thickness of fabricated zone plates was dictated by a π‐phase shift requirement for focusing of the x rays at 8 and 20 keV energies.

FEL development at the Advanced Photon Source

Construction of a single-pass free-electron laser (FEL) based on the self-amplified spontaneous emission (SASE) mode of operation is nearing completion at the Advanced Photon Source (APS) with initial experiments imminent. The APS SASE FEL is a proof-of-principle fourth-generation light source. As of January 1999 the undulator hall, end-station building, necessary transfer lines, electron and optical diagnostics, injectors, and initial undulators have been constructed and, with the exception of the undulators, installed. All preliminary code development and simulations have also been completed. The undulator hall is now ready to accept first beam for characterization of the output radiation. It is the project goal to push towards full FEL saturation, initially in the visible, but ultimately to UV and VUV, wavelengths.

A classical Hanbury Brown-Twiss experiment with hard X-rays

The classical Hanbury Brown–Twiss experiment has been conducted with hard X-ray synchrotron radiation at the Advanced Photon Source. The measured spatial coherence area of the X-ray beam is in good agreement with the prediction based on the vertical positron beam size.

The elliptical multipole wiggler project

The elliptical multipole wiggler (EMW) has been designed, constructed, and installed in the X13 straight section of the NSLS X-ray Ring. The EMW generates circularly polarized photons in the energy range of 0.1-10 keV with AC modulation of polarization helicity. The vertical magnetic field of 0.8 T is produced by a hybrid permanent magnet structure with a period of 16 cm. The horizontal magnetic field of 0.22 T is generated by an electromagnet, the core of which is fabricated from laminated iron to operate with a switching frequency up to 100 Hz. There are dynamic compensation trim magnets at the wiggler ends to control the first and second field integrals with very high accuracy throughout the AC cycle. The residual closed orbit motion due to the electromagnet AC operation is discussed.