Extending the q-range in wave-mixing spectroscopies

Place: conference hall, IMDEA Nanociencia.

Abstract: 

Investigating the thermal and vibrational behavior of nanoscale materials holds significant importance in advancing the technological applications of nano-electronic devices, such as smartphones and computer chips, by enabling faster, more efficient, and compact designs. The characteristics of materials, including elasticity, thermal conductivity, and heat capacity, are primarily influenced by collective lattice dynamics, which exhibit pronounced length-scale dependencies. These dependencies can significantly vary as spatial dimensions reduce from macroscopic to microscopic scales, approaching the size ranges of nanostructures.
Until now, understanding the thermoelastic response at the scale of tens of nanometers has been challenging due to the absence of experimental techniques capable of accessing this range without physically modifying or touching the sample. Such modifications introduce limitations in experimental design and complexities in data interpretation. Inelastic scattering of hard X-rays and thermal neutrons has proven effective in measuring collective lattice dynamics in condensed matter systems with wavevectors q > nm-1, while Brillouin scattering and optical transient grating (TG) techniques are suitable for q < 0.1 nm-1. However, the range of 0.1 - 1 nm-1 remains difficult to access despite efforts to extend Brillouin spectroscopy into the ultraviolet range and enhance the performance of X-ray spectrometers. Furthermore, these spectroscopic methods encounter limitations in instrumental resolution when measuring narrow lines, representing long-lived dynamics.
Recently, the emergence of free electron laser (FEL) sources has presented an opportunity to utilize extreme ultraviolet (EUV) and X-ray pulses with exceptional brilliance, facilitating the extension of non-linear optical techniques to shorter wavelengths. This advancement enables ultrafast investigations into nanometer regimes. The EUV TG approach has been successfully pioneered at the FERMI FEL using the dedicated endstation TIMER. In this seminar, I will present our latest work on Stimulated Brillouin scattering at a wavevector of 1 nm-1 achieved through the utilization of extreme ultraviolet transient gratings.