Ultrafast photo-acoustic spectroscopy of super-cooled liquids

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2010.Vita. Cataloged from PDF version of thesis.Includes bibliographical references (p. 219-231).Picosecond laser ultrasonic techniques for acoustic wave generation and detection were adapted to probe longitudinal and transverse acoustic waves in liquids at gigahertz frequencies. The experimental effort was designed for the study of supercooled liquids whose slower relaxation dynamics extend to gigahertz frequencies at high temperatures and whose faster dynamics are centered uniquely in the gigahertz frequency range. The experimental approach used a unique laser pulse shaping technique and, in the case of shear acoustic waves, a crystallographically canted metal transducer layer, to generate frequency tunable compressional and shear acoustic waves. Either time-domain coherent Brillouin scattering or interferometry was used to detect the waves in or after propagation through a liquid layer. The study of liquid-state gigahertz acoustic behavior required advances in both the experimental methodology and in the theoretical modeling of the results. A particular challenge was posed by the extraordinarily strong damping of gigahertz-frequency acoustic waves in liquids at some temperature ranges. This demanded the design and construction of a liquid sample cell allowing access to a wide range of liquid thicknesses, from less than a nanometer up to several microns. This was achieved by squeezing the liquid between two specially prepared high quality optical substrates held in a non-parallel configuration by a custom-designed sample holder jig. Several metallic layer materials were used for conversion of optical pulse energy into acoustic waves that were launched into the liquid samples, and different probe geometries were developed to enable access to a wide frequency range. The developed spectroscopic strategies were then applied to the study of two liquids, glycerol and tetramethyl tetraphenyl trisiloxane (DC704). Measurements of the density responses of both liquids from 400 K to below their respective glass transition temperatures were carried out. Longitudinal acoustic waves were either monitored via time-domain Brillouin scattering in the liquid or via interferometry after transmission through variably thick liquid layers, granting access to longitudinal acoustic frequencies from 10 GHz up to about 200 GHz. The information obtained on gigahertz frequency liquid relaxation was pieced together with data from several other techniques to create broadband relaxation spectra (from millihertz up to gigahertz), allowing characterization of the complex structural relaxation dynamics over many orders of magnitude and enabling both empirical modeling and testing of the predictions of the mode-coupling theory of supercooled liquids. The requirements for gigahertz shear wave generation and detection, including the properties of the photo-acoustic transducer materials, the sample and experimental geometry, and the detection material choices, are discussed. Results on shear wave propagation in glycerol and DC704 are presented. The technique for shear wave generation and detection is not limited to the study of viscous liquids but can also be applied to liquids like water, from which initial results are presented.by Christoph Klieber.Ph.D

Nonlinear Acoustics at GHz Frequencies in a Viscoelastic Fragile Glass Former

Using a picosecond pump-probe ultrasonic technique, we study the propagation of high-amplitude, laser-generated longitudinal coherent acoustic pulses in the viscoelastic fragile glass former DC704. We observe an increase of almost ten percent in acoustic pulse propagation speed of its leading shock front at the highest optical pump fluence which is a result of the supersonic nature of nonlinear propagation in the viscous medium. From our measurement we deduce the nonlinear acoustic parameter of the glass former in the GHz frequency range across the glass transition temperature.Comment: 5 pages, 3 figure

Optical Generation of Gigahertz-Frequency Shear Acoustic Waves in Liquid Glycerol

Picosecond laser ultrasonic techniques for acoustic wave generation and detection have been employed to probe shear acoustic waves in liquid glycerol at gigahertz frequencies. The experimental approach uses a unique laser pulse shaping technique and a crystallographically canted metal layer to generate frequency-tunable transverse acoustic waves, and uses time-domain coherent Brillouin scattering to detect the waves after they propagate through a liquid layer and into a solid substrate. A linear frequency dependence is found for both the shear speed and attenuation rate in glycerol.National Science FoundationDepartment of Energ

Picosecond shear waves in nano-sized solids and liquids

We will review recent progress on the generation and detection of picosecond shear acoustic waves. Examples will be shown in which the transverse isotropic symmetry of the sample structure is broken in order to permit shear wave generation through sudden laser heating. As an illustration of the technique, picosecond longitudinal and shear acoustic waves have been successfully employed to probe structural dynamics in nano-sized solids (gold nano-crystals assemblies) and nano-sized liquids (glycerol and water).National Science Foundation (Grants No. CHE-0616939 and DMR-0414895)CNRSDepartment of Energy (Grant No. DE-FG02-00ER15087

Time-domain Brillouin Scattering as a Local Temperature Probe in Liquids

International audienc

High frequency longitudinal and shear acoustic waves in glass-forming liquids

Three different picosecond ultrasonic techniques for longitudinal and transverse acoustic pulse generation have been combined with Impulsive Stimulated Thermal Scattering (ISTS) to probe structural relaxation dynamics in glycerol and DC704 (tetramethyl tetraphenyl trisiloxane) at megahertz and gigahertz frequencies (∼ 50 MHz - 100 GHz) from below their respective glass transition temperatures up to 370 K.United States. Department of Energy (Grant DE-FG02-00ER15087)National Science Foundation (U.S.) (Grant CHE-0616939)National Science Foundation (U.S.) (Grant DMR-0414895

Toward broadband mechanical spectroscopy

Diverse material classes exhibit practically identical behavior when made viscous upon cooling toward the glass transition, suggesting a common theoretical basis. The first-principles scaling laws that have been proposed to describe the evolution with temperature have yet to be appropriately tested due to the extraordinary range of time scales involved. We used seven different measurement methods to determine the structural relaxation kinetics of a prototype molecular glass former over a temporal range of 13 decades and over a temperature range spanning liquid to glassy states. For the material studied, our results comprise a comprehensive validation of the two scaling relations that are central to the fundamental question of whether supercooled liquid dynamics can be described universally. The ultrabroadband mechanical measurements demonstrated have fundamental and practical applications in polymer science, geophysics, multifunctional materials, and other areas.Comment: 7 pages, 6 figures, Supplementary: 16 pages, 20 figure

Coherent Brillouin spectroscopy in a strongly scattering liquid by picosecond ultrasonics

In a modification of a picosecond ultrasonic technique, a short acoustic pulse is launched into a liquid sample by a laser pulse absorbed in a semitransparent transducer film and is detected via coherent Brillouin scattering of a time-delayed probe pulse. With both excitation and probing performed from the transducer side, the arrangement is suitable for in vivo study of biological tissues. The signal is collected from a micrometer-thick layer next to the transducer and is not affected by the diffuse scattering of probe light deeper in the sample. The setup, utilizing a 33 nm thick single crystal SrRuO[subscript 3] transducer film, is tested on a full fat milk sample, with 11 GHz acoustic frequency recorded.United States. Dept. of Energy (DOE grant DE-FG02-00ER15087)National Science Foundation (U.S.) (grant IMR- 0414895)United States. Army Research Office (Institute for Soldier Nanotechnologies, contract DAAD-19-02- D-0002)United States. Army Research Office (grant W911NF-10-1- 0362