Leah Ruby Williams

Femtosecond time-resolved measurements of optic phonon dephasing by impulsive stimulated raman scattering in α-perylene crystal from 20 to 300 K

Abstract Excitation and detection of coherent optic phonons by impulsive stimulated Raman scattering (ISRS) is reported. The technique permits femtosecond time-resolved observations of optic phonon oscillations and dephasing. Decay rates of librational and translational optic phonons in α-perylene crystals have been measured in the temperature range 20–30 K.

Picosecond impulsive stimulated brillouin scattering: Optical excitation of coherent transverse acoustic waves and application to time-domain investigations of structural phase transitions

Abstract A practical stimulated Brillouin-scattering method for spectroscopic characterization of low-frequency excitations is extended to permit optical generation and detection of phase-coherent transverse, longitudinal, and mixed polarization acoustic phonons, tunable over a wide frequency range, in solid media. Results are presented for BK-7 glass and the KH 2 PO 4 crystal near its structural phase transition (SPT). Time-domain observations of acoustic phonon-induced ordering near SPTs in KH 2 PO 4 and KD 2 PO 4 were carried out, and applications of the technique to measurements of SPT dynamics are discussed.

Femtosecond time-resolved measurements of electronic excited-state relaxation in pyrene excimer-forming crystals

Abstract Femtosecond time-resolved transient grating experiments reveal an extremely fast relaxation process in pyrene excimer-forming crystals following electronic excited-state production via two-photon absorption. We interpret this as relaxation of the initially excited, delocalized exciton into the self-trapped, distorted excimer state.

Preliminary observation of nonrelaxational inertial motion in CS2 liquid by femtosecond time‐resolved impulsive stimulated scattering

Preliminary femtosecond time‐resolved impulsive stimulated scattering data from CS2 liquid are shown which clearly indicate an inertial component of the short‐time motion which cannot be described in terms of Debye relaxational dynamics. A discussion of time‐domain and frequency‐domain light scattering techniques is given to illustrate the comparative difficulty of characterizing this type of motion by conventional methods.

Subpicosecond excimer‐formation dynamics in organic molecular crystals

Subpicosecond excited‐state relaxation times in the organic molecular crystals pyrene and α‐perylene are observed via femtosecond time‐resolved transient absorption spectroscopy. Forward impulsive stimulated scattering with a single ultrashort excitation pulse is demonstrated in a crystal.

Femtosecond time‐resolved spectroscopy of coherent vibrational and electronic excitations in solids

‘‘Impulsive’’ stimulated scattering (ISS) of femtosecond laser pulses was used to coherently excite and probe a low‐lying (61‐cm‐1) electronic excitation in the cooperative Jahn‐Teller crystal, terbium vanadate. Coherent terahertz oscillations and their dephasing were observed in the time domain. ISS is a general aspect of ultrashort‐pulse interactions with matter, through which coherent excitations are produced whenever a sufficiently short laser pulse enters a Raman‐active medium. Its use for measurement of vibrational and electronic dephasing and lifetimes, and for time‐resolved spectroscopy of vibrationally distorted crystals and molecules, is discussed.