D.M. Mills

Time-resolved x-ray diffraction measurement of the temperature and temperature gradients in silicon during pulsed laser annealing

Nanosecond resolution time‐resolved x‐ray diffraction measurements have been used to study the temperature and temperature gradients in 〈100〉 and 〈111〉 oriented silicon crsytals during pulsed laser annealing. Thermal strain analysis of time‐resolved extended Bragg scattering has shown the lattice temperature to reach the melting point during 15‐ns, 1.5‐J/cm2 ruby laser pulses and to remain at the melting point during the high reflectivity phase (HRP). The temperature gradients at the liquid‐solid interface were found to be in the range of ∼107 K/cm during the HRP.

Time-Resolved X-ray Absorption Spectroscopy of Carbon Monoxide-Myoglobin Recombination After Laser Photolysis

Results are presented for the first time-resolved x-ray absorption measurements with a time resolution of 300 microseconds on a dynamically evolving chemical system. By synchronizing a neodymium: yttrium-aluminum-garnet pulsed laser with the bursts of x-rays emitted from the Cornell High Energy Synchrotron Source, it was possible to monitor at room temperature the recombination of carbon monoxide with myoglobin after laser photolysis. Changes in the pre-edge structure and in the position of the iron edge of this protein were detected as a function of time.

A fixed exit sagittal focusing monochromator utilizing bent single crystals

Abstract We have constructed and tested a tunable two crystal, horizontally focusing monochromator for use with synchrotron radiation. Horizontal focusing is achieved by using a segmented rectangular crystal especially cut to have the bending properties of a triangular plate. The bending device was designed to maintain axial symmetry around the central ray independent of bend radius. The entire crystal and bending device is so arranged that, coupled with the first crystal, a fixed exit beam height is maintained for all energies. Other innovative features such as an automatic translation seek circuit will be discussed.

The performance of a separated crystal X-ray monochromator during wiggler heating — Preliminary results☆

Abstract We report on the performance of a double crystal monochromator exposed to large heat loads from a 6 pole wiggler magnet running at 15.6 kG peak field and a 5.3 GeV electron beam. This source of synchrotron radiation can produce between 1.8 and 4.5 kW of X-ray power depending on beam conditions. Various single crystals of silicon have been tested in a nondispersive double crystal arrangement over a wide energy range along with several different cooling schemes. We report preliminary measurements of the performance of silicon crystals cooled by ambient helium gas or water cooled through conductive greases or through a 10 μm thick layer of liquid indium and gallium. A side cooled, thick crystal geometry shows good stability for photon energies from 20 to 45 keV. A thin, bottom cooled geometry shows promise at 7.4 keV. We have observed monochromator performance (rocking curve width, shift in edge, X-ray flux output vs electron beam current, harmonic rejection capabilities, etc.) under a variety of heating conditions. We summarize our suggestions for making effective use of monochromators under severe operating conditions.

Phase-plate performance for the production of circularly polarized X-rays

Abstract We have constructed a monolithic two-crystal phase-plate for use with high energy synchrotron radiation. The phase-plate can rotate the plane of polarization of an incident linearly polarized beam, or can be used to transform a linearly polarized beam to elliptically or circularly polarized X-rays. The X-ray optics of the phase-plate will be discussed along with test results at X-ray energies above 20 keV performed at CHESS.

Time‐resolved x‐ray study of Ge during pulsed laser melting

Nanosecond resolution time‐resolved x‐ray diffraction has been used to make the first measurements of the liquid‐solid interface overheating and undercooling in germanium. The results show an orientation‐dependent undercooling for growth on (111) and (001) faces. For both the (111) and (001) faces the velocity versus temperature interface response function has a slope of ∼5 K/(m/s), except for undercooling on the (111) face where the slope is 20 K/(m/s).

A separated crystal, fixed-exit monochromator for X-ray synchrotron radiation☆

Abstract A separated, two-crystal X-ray monochromator has been designed and constructed at CHESS, the Cornell High Energy Synchrotron Source. The device is tunable through a wide range of energies (3.5 to 21 keV with Si(111) crystals) by means of a single axis rotational stage, and maintains a fixed height for the exiting monochromatic beam. The system includes a novel design that allows quick changing and accurate repositioning of the monochromating elements. Details of the construction are presented along with the results of the preliminary testing.

Nanosecond resolved X-ray diffraction during pulsed laser annealing of silicon

Abstract The pulsed nature of the X-rays emitted from the Cornell High Energy Synchrotron Source (CHESS) was utilized to carry out a diffraction study of the near-surface structure and temperature of silicon following pulsed ruby laser annealing. To our knowledge, this was the first temporal X-ray diffraction investigation of a system at the nanosecond timescale. In this paper we describe experimental details concerning the synchronization of the laser with the X-ray bursts along with a description of the data collection technique and experimental results.

A tunable, fixed-exit, monolithic X-ray monochromator for synchrotron radiation sources☆

Abstract A novel X-ray monochromator has recently been built and tested at the Cornell High Energy Synchrotron Source (CHESS). It features all the inherent advantages of monolithic monochromators but also has a fixed exit height with respect to the incident beam. Applications and extensions of this design to other monochromating systems will be discussed.

High‐speed x‐ray sensitive photoconducting detector

A novel photoconducting detector for time‐resolved measurements in the x‐ray region of the spectrum has been constructed. Time resolution of better than 40 ps at energies between 3 and 10 keV has been demonstrated in bunch length measurements on the Cornell Electron Storage Ring. At high beam currents, dramatic instabilities and a breakup of the electron bunch were directly observed with this detector.