William T. Lotshaw

Femtosecond dynamics of the optical kerr effect in liquid nitrobenzene and chlorobenzene

Abstract The optical Kerr effect of liquid nitrobenzene and chlorobenzene is probed with 65 fs optical pulses at 633 nm. We observe an instantaneous signal contribution which is attributed to the incoherent (dephased) electronic component of the third-order nonlinear susceptibility χ (3) . Additionally, three non-instantaneous relaxation components are observed in each liquid, including an ultrafast relaxation with an 80 fs lifetime and the previously observed orientational relaxations. A third relaxation component is observed in both liquids with a lifetime on the order of 450 fs. The prevailing diffusional theory of the optical Kerr effect fails to describe the temporal profile of the measured response in both liquids.

Femtosecond laser-induced optical Kerr dynamics in CS2/alkane binary solutions

Abstract Our original Letter contained insufficient information to reproduce the fitted experimental curves. This Comment provides the missing information.

Femtosecond Raman-induced Kerr effect. Temporal evolution of the vibrational normal modes in halogenated methanes☆

Abstract We report a direct observation of the temporal evolution of coherently excited intramolecular normal-mode vibrations in chloroform and carbon tetrachloride using a time-resolved analog of optically heterodyned Raman-induced Kerr effect spectroscopy (OHD RIKES). The observed tetraherz oscillations are well described in terms of independently evolving harmonic oscillators driven through a stimulated Raman process involving the different Fourier components of the 75 fs laser pulse.

Observation of low-frequency Raman modes in several halogenated methanes by the optical Kerr effect

The time-resolved optical Kerr effect was used to probe the ultrafast relaxation of four halogenated methanes, CHCl3, CBrCl3, CHBr3 and CFBr3. A 65 fs coherent laser pulse from a synchronously pumped antiresonant ring dye laser with Fourier components ranging over 300 cm−1 is separated into a pump and a probe beam, aligned for heterodyne detection of the Kerr signal. The present paper focuses on the intramolecular vibrational resonant component of the relaxation curve, corresponding to low-frequency (< 300 cm−1) Raman modes of the halogenated methanes that are coherently excited by the spectrally broad laser pulse. It is demonstrated that some symmetric modes, as well as asymmetric modes, are detectable by the optical Kerr effect, the probability of this depending on the depolarization ratio of the mode, and hence its anisotropy.

Investigation Of Ultrafast Molecular Dynamics Of Liquids Via Coherent, Time-Resolved Fourier Transform Spectroscopy

The molecular dynamics of liquids in the frequency range 100 GHz to tens of THz are conveniently interrogated with broadband femtosecond laser pulses through the time resolved optical Kerr effect. .The molecular dynamics are extracted from the data by a combination of the traditional semi-log plot analysis for diffusive relaxations, and a novel Fourier transform analysis for the intra- and inter molecular vibrational dynamics. These techniques are applied to the optical Kerr dynamics of liquid iodobenzene at room temperature, providing evidence for the presence of both librational motion (at short times) and diffusive reorientation (at longer times) about two distinct molecular axes.

Ultrafast Nonlinear Laser Spectroscopy: The Role Of Inertia In The Femtosecond Dynamics Of The Optical Kerr Effect In Molecular Liquids

The optical Kerr response of liquid CS2, nitrobenzene and chlorobenzene is probed with 65 femtosecond optical pulses centered at 633 nm. We observe a clearly separable instan-taneous signal contribution in each system that is attributed to the incoherent (dephased) electronic part of the third order nonlinear susceptibility χ(3). In addition to this instantaneous component, each system exhibits a multicomponent decay characterized by two components in CS2 and three in the substituted benzenes. Finally, we note that the prevailing theory of the optical Kerr effect fails to describe the short time behavior of the measured response in each liquid, apparently requiring the inclusion of an inertial term in the equation of motion for the induced birefringence.

The structure and dynamics of molecular liquids probed with femtosecond optical Kerr effect spectroscopy

The dynamical behavior of simple molecular liquids is investigated using the time‐resolved optical Kerr effect. These studies provide direct information on the distribution of molecular environments in the various liquids, and give insight into the local intermolecular potentials. The effects of variations in the intermolecular potential on the various relaxation components of CS2 are investigated through dilutions in effectively inert alkane solvents. The interaction‐induced contributions to the induced birefringence are observed to increase with decreasing CS2 concentration.

Femtosecond molecular motions and implications for electron solvation dynamics in liquids

Abstract Molecular motions at femtosecond times are observed experimentally, via nonlinear laser spectroscopy, as responses to the imposition of a sudden, intense laser field in the optical Kerr effect. The electronic, librational, collision-induced translational and reorientational diffusional motions identified through the nonlinear polarizability responses are linked to the probable responses of the disordered medium to an excess electron undergoing multiple scattering at times -12 s.