Seminars Archive

Active X-Ray Optics for Synchrotrons

Abstract
I will report on our recent developments of solid state based Active X-ray Optics. In total we will present three different approaches for the active manipulation of hard x-rays at synchrotron beamlines. The first method presented in this contribution is a surface acoustic wave (SAW) pulse picker [1]. The scheme relies on electromechanical generation of a SAWsin piezoelectric crystals. In our experiments we employ LiNbO3 (LNB) single crystals with Inter Digitated Transducers (IDTs) deposited on the surface. The IDTs are connected to an amplified RF signal that is controlled by a pulse generator. Upon trigger, an RF burst is applied to the IDT and generates on-demand SAWs which propagate along the crystal surface. The acoustic deformation acts as a grating for X-rays and results in sidebands of the Bragg peak of the LNB crystal. The scheme has been employed previously to isolate single X-ray pulses from a hybrid bunch filling, thus demonstrating a switching time in the order of 100 ns. We will present new experimental data showing that a similar scheme can be employed to generate bursts x-ray pulse sequences of arbitrary length from 100 nanoseconds to micro- and millisecond duration. The second example discussed in this contribution is a picosecond Bragg switch, the so-called PicoSwitch, for shortening a synchrotron x-ray pulse to few picoseconds. The device was installed for a benchmark experiment at the ID09 beamline at the European Synchrotron Radiation Facility ESRF [2]. We employ the PicoSwitch to probe structural dynamics induced by propagating coherent phonons in thin film heterostructures. The PicoSwitch uses a photoacoustic mechanism where a short optical excitation pulse launches coherent shockwaves that modulate the lattice parameter of a dedicated switching layer in the PicoSwitch structure. A synchrotron x-ray pulse impinging the switch at the correct incidence angle is only diffracted while the coherent shockwave is present in the switching layer, i.e., typically for 5-10 ps. Coherent structural dynamics simulations show that even shorter pulse durations can be achieved. We will discuss design parameters as well as efficiency and switching contrast of the PicoSwitch in different experimental environments. The third method relies on laser-induced thermal transient gratings (TTGs). The TTGs are excited in oxide heterostructures especially designed to generate large thermal deformations upon optical excitation. TTGs consist of periodic surface deformations with a height of few nanometers [3] that can be generated and controlled [4] in time by short laser pulses. Diffraction of hard x-rays from such deformations can reach an efficiency of more than 30 %[5]. We will present experimental results of this method employed for pulse picking at P23 beamline at Petra III, Desy [6]. References: [1] S. Vadilonga et al., Optics Lett. 42, 1915 (2017) [2] M. Sander et al., J. Synch. Rad. 26, 1253-1259 (2019) [3] R. Shayduk and P. Gaal, J. Appl. Phys. 127, 073101 (2020) [4] J.-E. Pudell et al., Phys. Rev. Applied 12, 024036 (2019) [5] M. Sander et al., Appl. Phys. Lett. 111, 261903 (2017) [6] D. Schmidt et al., J. Synch. Rad. 28, 375-382 (2021)