$xray diffraction gratings thesis$

Hard X-ray Transient Grating Spectroscopy on Bismuth Germanate

The ability to probe bulk properties of materials using ultrafast nonlinear optical spectroscopy has been a topic of significant interest in recent years. In this context, transient grating (TG) spectroscopy has emerged as a powerful technique for studying vibrational, magnetic, and electronic degrees of freedom in the time domain. This technique relies on the diffraction of an optical probe pulse by a coherent phonon excited by a non-resonant TG excitation.

In bismuth germanate (BGO), the non-resonant TG excitation generates coherent optical phonons that can be detected as a function of time. However, this technique has traditionally been limited to the visible and near-infrared regimes due to the availability of suitable sources. The development of coherent X-ray free-electron laser sources has now made it possible to extend TG spectroscopy to the hard X-ray regime.

The advantages offered by X-rays for TG spectroscopy are numerous. Their large penetration depth allows probing the bulk properties of materials, while their element specificity enables addressing core excited states. Additionally, their short wavelengths create excitation gratings with unprecedented momentum transfer and spatial resolution.

$xray diffraction gratings thesis$

In this study, we demonstrate TG excitation in the hard X-ray range at 7.1 keV using a novel experimental setup that combines diffractive optics with ultrafast heterodyne-detected transient-grating spectroscopy. Our results show that this technique can be used to probe bulk properties of materials and paves the way for ultrafast coherent four-wave-mixing techniques involving nanoscale TG spatial periods.

$xray diffraction gratings thesis$

The extension of TG spectroscopy to the X-ray regime opens up new possibilities for studying a wide range of phenomena in condensed matter physics, including spin dynamics, charge carrier transport, and phase transitions. Furthermore, the ability to probe core excited states using X-rays offers a powerful tool for understanding the behavior of correlated electrons in complex materials.

Overall, our work demonstrates the potential of hard X-ray transient grating spectroscopy as a new tool for investigating the properties of materials at the nanoscale.

$xray diffraction gratings thesis$

Xray diffraction gratings thesis