Spatiotemporal Coherent Control of Thermal Excitations in Solids.

Area of Science:

• Ultrafast science
• Surface dynamics
• X-ray diffraction techniques

Background:

• Femtosecond laser excitation creates transient gratings (TG) on surfaces.
• Understanding the interplay of thermal and acoustic effects in TG is crucial for controlling surface dynamics.

Purpose of the Study:

• To demonstrate spatiotemporal coherent control of thermally induced surface deformations on ultrafast timescales.
• To explore the potential of TG for developing ultrafast x-ray shutters.

Main Methods:

• Utilizing X-ray reflectivity measurements to probe transient gratings.
• Employing grazing incidence x-ray diffraction for sub-Ångström resolution measurements of surface deformations.
• Analyzing the dynamics of femtosecond TG excitations as a superposition of acoustic and thermal gratings.

Main Results:

• Achieved unambiguous measurement of transient surface deformation amplitudes with sub-Ångström resolution.
• Demonstrated the cancellation of the dominant thermal grating component by a time-delayed, spatially shifted excitation.
• Identified the potential for creating an ultrafast x-ray shutter by controlling thermal grating dynamics.

Conclusions:

• Spatiotemporal coherent control of femtosecond laser-induced transient gratings is feasible.
• The developed methods offer new avenues for coherent control in x-ray diffraction experiments.
• Detailed analysis of thermal and acoustic dynamics provides insights into the speed limits of ultrafast x-ray shutters.