C. Benson

A hard X-ray nanoprobe beamline for nanoscale microscopy

The Hard X-ray Nanoprobe Beamline is a precision platform for scanning probe and full-field microscopy with 3–30 keV X-rays. A combination of high-stability X-ray optics and precision motion sensing and control enables detailed studies of the internal features of samples with resolutions approaching 30 nm.

Reconstruction of an astigmatic hard X-ray beam and alignment of K-B mirrors from ptychographic coherent diffraction data.

We have used coherent X-ray diffraction experiments to characterize both the 1-D and 2-D foci produced by nanofocusing Kirkpatrick-Baez (K-B) mirrors, and we find agreement. Algorithms related to ptychography were used to obtain a 3-D reconstruction of a focused hard X-ray beam waist, using data measured when the mirrors were not optimally aligned. Considerable astigmatism was evident in the reconstructed complex wavefield. Comparing the reconstructed wavefield for a single mirror with a geometrical projection of the wavefront errors expected from optical metrology data allowed us to diagnose a 40 μrad misalignment in the incident angle of the first mirror, which had occurred during the experiment. Good agreement between the reconstructed wavefront obtained from the X-ray data and off-line metrology data obtained with visible light demonstrates the usefulness of the technique as a metrology and alignment tool for nanofocusing X-ray optics.

A beamline for 1–4 keV microscopy and coherence experiments at the Advanced Photon Source

The third‐generation Advanced Photon Source will open up dramatic new opportunities for experiments requiring coherent x‐rays, such as scanning x‐ray microscopy, interferometry, and coherent scattering. We are building a beamline at the Advanced Photon Source to exploit the potential of coherent x‐ray applications in the 1–4 keV energy region. A high brightness 5.5‐cm‐period undulator supplies the coherent x‐rays. The beamline uses horizontally deflecting grazing‐incidence optical elements to preserve the coherence of the undulator beam. The optics have multilayer coatings for operation at energies above 1.5 keV. This paper discusses the beamline design and its expected performance.

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.

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.

Present status and recent results from the APS SASE FEL

The Low-Energy Undulator Test Line (LEUTL) at the Advanced Photon Source, Argonne National Laboratory, is intended to demonstrate the basic operation of a SASE-based free-electron laser. Goals include comparison of experimental results With theoretical predictions and scaling laws, identification of problems relevant to fourth-generation light source construction and operation and the means of addressing them, the development of operational and diagnostic techniques to optimize SASE FEL performance and increase repeatability from run to run. and performance of initial pioneering experiments capable of exploiting the unique properties of the laser. The basic layout and operational philosophy of the LEUTL experiment is presented. A summary of past results, including saturation, is reviewed, and a description of recent results is presented. We conclude with future plans, which include pressing to shorter wavelengths and incorporating user experiments into the LEUTL experimental program. (Less)

Conceptual Design For A Beamline For A Hard x‐ray Nanoprobe with 30 nm Spatial Resolution

The planned Center for Nanoscale Materials (CNM) at Argonne National Laboratory is aimed at the development and study of the properties of nanomaterials and nanodevices. As part of the characterization instruments at CNM, we are developing a new hard x‐ray nanoprobe beamline at the Advanced Photon Source. The beamline will provide microscopy and spectroscopy for photon energies from 3 keV to 30 keV. Hard x‐ray zone plates will be used to achieve a spatial resolution of 30 nm in the 3 – 10 keV region. Two operational modes will combine the speed of a transmission x‐ray microscope with the analytic capabilities of a hard x‐ray microprobe. The major operation mode will be a scanning probe mode, where spatially coherent radiation is focused into a diffraction‐limited spot to excite secondary signals in the specimen. This will allow elemental mapping and spectroscopy at high sensitivity using x‐ray fluorescence, or strain contrast imaging using x‐ray diffraction. A secondary mode will use partially coherent ra...

Utilization of CTR to measure the evolution of electron-beam microbunching in a self-amplified spontaneous emission (SASE) free-electron laser (FEL)

We report on the first measurements of the z-dependent evolution of electron-beam microbunching as revealed through coherent transition radiation (CTR) measurements in a visible self-amplified spontaneous emission free-electron laser experiment. The increase in microbunching was detected by tracking the growth of the visible CTR signals as generated from insertable metal mirrors/foils after each of the last three undulators. The same optical imaging diagnostics that were used to track the z-dependent intensity of the undulator radiation (UR) were also used to track the electron beam/CTR information. Angular distribution, beam size, and intensity data were obtained after each of the last three undulators in the five-undulator series, and spectral information was obtained after the last undulator. The exponential growth rate of the CTR was found to be very similar to that of the UR and consistent with simulations using the code GENESIS.

UV-VUV diagnostics for the Advanced Photon Source SASE FEL

The Advanced Photon Source self-amplified spontaneous emission (SASE) free-electron laser (FEL) uses diagnostics between undulator sections to characterize the light and the electron beam. These diagnostics enable z-dependent measurements of the exponential growth of the radiation and of the microbunching. The original diagnostics were designed for visible light. To enable measurements down to 265 nm, UV-enhanced cameras and fused-silica lenses have been installed. We have now designed a diagnostics suite that will enable us to continue measurements down to 50 nm using reflective optics and back-illuminated CCD cameras operating in vacuum. We describe the enhancements to the diagnostics for operation in the UV and VUV.

Hard X-ray polarizer to enable simultaneous three-dimensional nanoscale imaging of magnetic structure and lattice strain

The performance of a diamond X-ray phase retarder to enable the production of circularly polarized X-rays has been quantitatively measured and magnetic dichroism contrast in transmission and diffraction geometries has been demonstrated. Feasibility tests for dichroic Bragg coherent diffractive imaging experiments were performed and showed that the diamond X-ray phase retarder does not produce significant distortions to the X-ray wavefront and that Bragg coherent diffractive imaging reconstructions are achievable.