High frequency viscous relaxation from the Brillouin spectra of n‐pentanol

Background-free Brillouin spectroscopy in scattering media at 780 nm via stimulated Brillouin scattering

We demonstrate the effectiveness of stimulated Brillouin scattering for background-free Brillouin spectroscopy in scattering media within the biological spectral window. Using two nearly counter-propagating continuous-wave diode laser beams at 780 nm, we acquired transmission stimulated Brillouin point spectra in 10 mm and 500 μm thick Intralipid tissue phantoms with ∼100  μm and ∼16  μm diameter focal points, respectively. Stimulated gain spectra with high signal-to-noise ratio (8.7-30.7 dB) and frequency accuracy (6-72 MHz) were obtained at 20  MHz/10  ms and 20  MHz/100  ms through 0.24-3.36 mean-free paths of tissue phantoms. Our results suggest that stimulated Brillouin gain can be useful for imaging of Brillouin resonances in submillimeter-thick scattering samples.

Dynamic light scattering in liquid and supercooled diphenylmethane

We use a dynamic light scattering technique to measure both polarized (VV) and depolarized (VH) spectra of liquid diphenylmethane (DPM) between 288 and 362 K, covering both normal and supercooled liquid ranges. Our results allow extracting information on structural relaxation processes, rotational motions, rotation-translation couplings, and molecular reorientation phenomena in liquid DPM. The VV spectra are modeled according to the microscopic theory of Wang, which assumes that a structural relaxation process dominates the spectrum. We find that the relaxation time of the structural relaxation in DPM follows an Arrhenius behavior. The Rayleigh dip was observed in the VH spectra, which are described using the Andersen-Pecora theory. Our results are discussed in terms of the rotation-translation coupling parameter, which we find independent of temperature over the experimental range. The collective reorientation time also follows an Arrhenius behavior with temperature. Finally, we calculate the hydrodynamic volumes for the reorientation process from geometric molecular models in two hydrodynamic limits: slip and stick boundary conditions. Our results suggest that the DMP molecule reorientates in quasi-slipping conditions in the bulk liquid.