Impulsive stimulated scattering of surface acoustic waves on metal and semiconductor crystal surfaces

Frequency comb enhanced Brillouin microscopy

Brillouin light scattering (BLS) microscopy is a well established and powerful technique to study acoustic and magnetic excitations in the frequency domain with sub-micron spatial resolution. Many other spectroscopic techniques have benefited from the introduction of femtosecond laser sources to optically pump and stimulate the sample under investigation. In BLS microscopy, the use of femtosecond lasers as the excitation source introduces several challenges, primarily since the measured frequency shift is small and the signal levels are weak due to the low duty cycle of typical femtosecond lasers. Here we present a method to evade these challenges. A strong enhancement of the weak scattering amplitude on selected modes is observed by pumping the sample with a high repetition rate frequency comb laser source. The laser beam can be focused to the diffraction limit, providing a micron pumping area. We can thus preserve the innate high frequency and spatial resolution of BLS microscopy. Furthermore, we are able to induce a point-like source of mode-selected elementary excitations which propagate away from the pumping spot. We conclude that we have demonstrated frequency comb pumped BLS microscopy as an attractive tool for studies of ultrafast induced laser dynamics directly in the frequency domain.

Line-scanning Brillouin microscopy for rapid non-invasive mechanical imaging

Brillouin spectroscopy probes the mechanical properties of material by measuring the optical frequency shift induced by photon-phonon scattering interactions. In traditional configurations, Brillouin spectrometers measure only one point of the sample at a time. This results in long acquisition times for mechanical imaging of large areas. In this work, we demonstrate a parallel detection configuration where the Brillouin shift of hundreds of points in a line can be measured simultaneously. In mm-sized samples, this novel configuration effectively shortens the acquisition time of two-dimensional Brillouin imaging from hours to tens of seconds, thus making it a powerful technology for label-free mechanical characterization of tissue and biomaterials.