Ultrafast switching of hard X-rays

Abstract

A new concept for shortening hard X-ray pulses emitted from a third-generation synchrotron source down to few picoseconds is presented. The device, called the PicoSwitch, exploits the dynamics of coherent acoustic phonons in a photo-excited thin film. A characterization of the structure demonstrates switching times of ≤ 5 ps and a peak reflectivity of ∼10(-3). The device is tested in a real synchrotron-based pump-probe experiment and reveals features of coherent phonon propagation in a second thin film sample, thus demonstrating the potential to significantly improve the temporal resolution at existing synchrotron facilities.

Communication: Demonstration of a 20 ps X-ray switch based on a photoacoustic transducer

“…3(b)]. By selecting a suitable delay (peak of Gaussian pulse at 50 ps after the laser illumination), one can reduce the incoming 100 ps X-ray pulse to a 20 ps pulse with a temporal contrast of C 0  = 9 and C ∞  = 4, defined as $C_{0,\infty }=\frac{{\eta }_{max}-{\eta }_{0,\infty }}{{\eta }_{0,\infty }}$, where $\eta$ is the diffraction efficiency before (${\eta }_0$), after (${\eta }_{\infty }$), and at the maximum (${\eta }_{max}$) of the switch action 11 . When comparing with the simulation (dot-dashed red curve in Fig.…”

“…This switch can reduce the pulse duration of the 100 ps X-ray pulse to 20 ps with a contrast of C 0  = 9, C ∞  = 4, and a peak reflectivity of 8%. Based on another concept, the PicoSwitch 11 can reduce the pulse duration to 2 ps with a contrast of C 0  = 50, C ∞  = 7 however at the expense of the peak reflectivity of 0.1%. For studies that require high throughput and can afford a temporal resolution of 20 ps, we believe that the gold/InSb switch can find application.…”

“…A more successful approach has been to utilize zone-folded acoustic phonons in a superlattice 10 . This switch generated a train of pulses; however, the concept was later improved by generating the strain wave in a thin metallic oxide film coated on top of an acoustically matched dielectric substrate (PicoSwitch 11,12 ). The PicoSwitch has a few ps temporal response, a high temporal contrast but a diffraction efficiency of about 0.1%–0.5%.…”

Evaluating scintillator performance in time-resolved hard X-ray studies at synchrotron light sources

“…A three-wheel chopper design has been demonstrated on ID09B, ESRF, which is able to isolate a single bunch from any of the ESRF bunch structures (Cammarata et al, 2009), and, more recently, a chopper research papers capable of delivering 50 ps, 8 keV pulses with a 1.25 MHz repetition rate has been developed at BESSY II (Fö rster et al, 2015). More complex shuttering techniques, such as phonon Bragg switching (Bucksbaum & Merlin, 1999), continue to be developed as a method to isolate single X-ray bunches (Gaal et al, 2014). Currently, the engineering and technical challenges, particularly the complications due to a high heat load, associated with bunch structure chopping means they are not yet commonplace on synchrotron beamlines, and thus have not been included in this review.…”

Picosecond pump–probe X-ray scattering at the Elettra SAXS beamline

“…Which physical or chemical ISSN 1600-5775 phenomenon is tracked during the experiment depends on the wavelength of the probe pulse. Here, scattering of picosecond pulses in the hard or medium X-ray regime offers the unique possibility to capture light-induced structural motion at the atomic level, such as, for example, crystalline lattice vibrations (Briggs et al, 2019;Gaal et al, 2014), nano-scale heat transport (Plech et al, 2004;Shayduk et al, 2016) and molecular rearrangement (Ihee et al, 2005;Cammarata et al, 2008). While alternative sources such as free-electron lasers (McNeil & Thompson, 2010;Helml et al, 2014) or laboratory setups (Weisshaupt et al, 2014;Bargheer et al, 2004) of picosecond (or shorter) X-ray pulses are generally available, they are either difficult to access or provide only low flux compared with synchrotron radiation.…”