W. Tandy Grubbs

cw stimulated Brillouin gain spectroscopy of liquids

Abstract We demonstrate the use of cw stimulated Brillouin gain (SBG) spectroscopy to measure high resolution Brillouin spectra of liquids. Results are reported for thirteen liquids at room temperature, all obtained in a polarized (VV) configuration with a scattering angle of 178°. The observed Brillouin frequencies compare favorably with those predicted on the basis of previous spontaneous Brillouin light scattering measurements. The narrow Brillouin bands of carbon disulfide (70 MHz half-width at half-maximum) are easily resolved in the SBG experiment, and the sensitivity is sufficient to detect the Mountain mode in the SBG spectrum of carbon tetrachloride.

High resolution stimulated Brillouin gain spectrometer

We describe a stimulated Brillouin gain (SBG) spectrometer based on low power continuous‐wave frequency‐stabilized lasers. The high resolution and broad tuning range of this spectrometer are demonstrated through a SBG spectrum of glycerol in the glassy state (T=146 K). The narrow Brillouin linewidth (17 MHz half‐width at half‐maximum) and large Brillouin shift (17.31 GHz) in this spectrum illustrate the extremely high equivalent ‘‘finesse’’ of the instrument, a finesse that would be difficult to achieve through interferometric techniques. The accuracy and precision with which the Brillouin shift can be measured are demonstrated using SBG spectra of liquid methylene chloride as an example. Our Brillouin shift values obtained over the temperature range 178–300 K are in excellent agreement with values measured previously by others using spontaneous and stimulated Brillouin scattering.

Dynamics in supercooled glycerol by high resolution stimulated Brillouin gain spectroscopy

We have used high resolution stimulated Brillouin gain spectroscopy to probe the dynamics of glycerol over the temperature ranges 146 to 305 K and 401 to 534 K, which include both the supercooled liquid and glass regimes. The high resolution and large spectral range of the technique have allowed us to resolve Brillouin peaks at low temperatures (146 K) with widths as narrow as 13 MHz and shifts as large as 17.3 GHz. A comparison of the observed Brillouin shifts and linewidths with predictions based on previous work at lower frequencies indicates that the main dispersion in our data arises from the primary (α) structural relaxation processes. However, this comparison also reveals that additional relaxation processes, perhaps associated with the secondary (β) processes, contribute to the Brillouin linewidths both above and below the glass transition. Our results also show a distinct kink in the temperature dependence of the speed of sound at 187 K, the glass transition temperature.

High‐resolution stimulated Brillouin gain spectroscopy of liquid carbon disulfide: Dependence of the linewidths and peak gain on scattering angle

We have used narrow linewidth continuous‐wave lasers to obtain high‐resolution stimulated Brillouin gain (SBG) spectra of liquid carbon disulfide at various scattering angles. For back‐scattering angles, the linewidths of the SBG peaks reflect the natural lifetimes of the stimulated acoustic waves, whereas for forward‐scattering angles the linewidths are dominated by laser jitter and by the uncertainty in the scattering wave vector that results from focusing the laser beams in the interaction region. The peak gain for the forward‐scattering SBG spectra is an order of magnitude smaller than that observed at a back‐scattering angle of 178°. The dependence of the peak gain on scattering angle can be accounted for quantitatively by considering the angle dependencies of the Brillouin frequency, linewidth, and laser beam crossing efficiency.

The JCE Data-Driven Exercises Digital Collection

Five peer-reviewed exercises are briefly described that have recently been added to the collection that focus upon various topics in physical, polymer, and organic chemistry.