Control of synchrotron x-ray diffraction by means of standing acoustic waves

Abstract

Synchrotron x-ray diffraction measurements in quartz crystals of different thickness excited by standing acoustic waves were carried out at the Advanced Photon Source of Argonne National Laboratory. We demonstrated the ability to significantly modify the quartz rocking curves for 20–25 keV x rays by changing the shear wave parameters in the frequency range between 15 and 105 MHz. Dynamic deformation introduced into the crystal lattice by acoustic waves resulted in a remarkable broadening of the rocking curves. The broadening effect strongly depends on the strength of the ultrasound, which can be easily regulated by changing the acoustic amplitude or frequency near the resonance. The maximum rocking curve broadening reached 17 times, which corresponds to the wavelength band, Δλ/λ=4×10−3, when used as a monochromator or analyzer for 20–25 keV x rays. The initial rocking curve shape is restored by sweeping the acoustic frequency within a 50–100 kHz range near the resonance. The tunable broadening effect allows effective manipulation of x-ray intensities in time domain. Time-resolved x-ray diffraction measurements under a 19.6 MHz acoustic wave excitation were performed by synchronizing the acoustic wave and x-ray burst periodicity. We used the fact that twice per period the standing wave produces a zero net deformation across the crystal thickness. By introducing an oscillating delay to the acoustic excitation, we were able to effectively change the phase of the acoustic wave relative to the x-ray burst periodicity. The x-ray diffraction intensity was strongly affected by tuning the timing of the x-ray arrivals to the minimum or maximum acoustic deformation. A deep modulation of x rays was observed in a wide frequency range between 0.1 Hz and 1 MHz, which certifies that acoustically excited quartz crystals can potentially be used as slow and fast x-ray modulators with high duty cycle.

Laboratory time-resolved X-ray diffractometry for in situ studies of crystalline materials under uniaxial compression and vibration

“…For example, in piezoelectric crystals, vibrations can cause electric fields. An effective method for generating a vibration load in a crystal is to excite an ultrasonic standing acoustic wave with MHz (Liss et al, 1997;Zolotoyabko & Quintana, 2004) or kHz (Kovalchuk, 2011;Blagov et al, 2013) frequency with an alternating electric field. This approach provides an opportunity to selectively excite crystal vibrations with large amplitude in a particular crystallographic direction.…”

Demonstration of a picosecond Bragg switch for hard X-rays in a synchrotron-based pump–probe experiment

“…The idea of switching a synchrotron x-ray pulse a) Electronic mail: pgaal@physnet.uni-hamburg.de with a controlled lattice deformation is almost 50 years old 12 . Since then, several attempts were made that relied on piezoelectric excitation 13,14 , generation of optical 15,16 and acoustic 17,18 phonons or picosecond thermal 19 excitations. Our device, which we call the PicoSwitch, is tested in a synchrotron-based optical pump -x-ray probe experiment to measure propagation of sound waves in epitaxial nanometer thin films.…”

“…The idea of switching a synchrotron X-ray pulse with a controlled lattice deformation is almost 50 years old (Allam, 1970). Since then, several attempts have been made that relied on piezoelectric excitation (Grigoriev et al, 2006;Zolotoyabko & Quintana, 2004), the generation of optical (Bucksbaum & Merlin, 1999;Sheppard et al, 2005) and acoustic phonons (Gaal et al, 2014;Sander et al, 2016) or picosecond thermal excitations (Navirian et al, 2011). Our device, which we call the PicoSwitch, has been tested in a synchrotronbased optical pump-X-ray probe experiment to measure the propagation of sound waves in epitaxial nanometer thin films.…”

Ultrafast switching of hard X-rays

“…Several early attempts were made to manipulate the time structure of the synchrotron X-ray pulse directly. Early experiments reported switching of hard X-rays resulting in pulses of 100 ps duration and more (Wark et al, 1989;Zolotoyabko & Quintana, 2004;Allam, 1970;Grigoriev et al, 2006;Navirian et al, 2011). A promising concept is based on optical phonons (Bucksbaum & Merlin, 1999); however, this could not yet be realised experimentally (Sheppard et al, 2005).…”