Time-resolved Optical Kerr Effect Research Articles

Ultrashort orientational dynamics of liquid crystals in the smectic-A phase

A femtosecond time-resolved optical Kerr effect experiment was carried out to study the reorientational motion of a series of cyanobiphenyl molecules around their long axis in the smectic-A phase. The Kerr effect was found to mainly result from the reorientation of the cyanobiphenyl core of the liquid crystal molecule. Three relaxation times were observed in the subpicosecond and picosecond range. They appear to be associated with libration and diffusive reorientations of chromorphores of individual and paired molecules. The analysis on several temporal scales reveals the existence of strong molecular interactions within the smectic-A layers.

Intra- and inter-molecular modes reflected in femtosecond time-resolved optical heterodyne-detected optical Kerr effect signal of molecules in liquids

We present a theoretical work on the femtosecond time-resolved optical heterodyne-detected optical Kerr effect (OHD-OKE) measurement of molecules in liquids to clarify the role of intra- and inter-molecular low-frequency modes. An expression for the signal of the OHD-OKE measurement is derived on the basis of the double space representation. The theory is applied to the system of neat chloroform at room temperature. A Raman active vibrational mode with a frequency of 262cm −1 is considered, together with rotational degrees of freedom or Raman active inter-molecular vibrational modes. All the vibrational modes are assumed to be harmonic. For simplicity, a free and diffusive rotor model is adopted. A quantum mechanical treatment is also used to take into account rovibrational dephasings. The reorientational relaxation is treated in the Debye-Einstein model. Effects of the rovibrational dephasing appear in the OHD-OKE signal in a subpicosecond time regime, but intra-molecular quantum beats disappear in the early time region compared with the experimental signal. The effects of the reorientational relaxation appear in a picosecond time regime. Inclusion of inter-molecular vibrational modes qualitatively explains the OHD-OKE measurement, although calculations by the present model are only approximate.

Pore-size-dependent orientational dynamics of a liquid crystal confined in a porous glass.

Time-resolved transient grating optical Kerr effect experiments were used to investigate the collective reorientational dynamics of pentylcyanobiphenyl embedded in the nanometer-length-scale pores of silica glasses. Measurements in the bulk pretransitional temperature range show a drastic decrease of the relaxation time of the order-parameter fluctuations compared to the bulk with a pronounced pore-size dependence. A Landau model based on independent pore segments can explain the pore-size dependence, but cannot satisfactorily reproduce the observed nonexponentiality of the decays.

Time-Resolved Photoinduced Absorption and Optical Kerr Effect in Fullerene C60

Abstract Time-resolved photoinduced absorption in fullerene C60 solutions is reported. The nonlinear index of refraction n2 and third-order susceptibility x (3) in C60 film, measured by the optical Kerr gate technique, are also reported.

Influence of surface interaction on the reorientational dynamics of pentylcyanobiphenyl confined in a porous glass

Time-resolved transient grating optical Kerr effect experiments were employed to investigate the reorientational dynamics of pentylcyanobiphenyl confined in the nanometer lengthscale pores of silica glasses. Temperature and pore-size-dependent measurements show the drastic influence of geometrical restriction on the cooperative reorientational motion in the nematogenic liquid. At temperatures far above the phase transition, a bulk phase and a distinct surface layer with different dynamic properties are observed. With pore size reduction,to 25 Å, a decrease of the surface layer thickness and an increase of the surface layer relaxation time are found. This is attributed to the modification of the surface layer structure by geometrical factors, e.g., the pore curvature.

Time-Resolved Optical Kerr Effect Measurements in Aqueous Ionic Solutions

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTTime-Resolved Optical Kerr Effect Measurements in Aqueous Ionic SolutionsI. Santa, P. Foggi, R. Righini, and J. H. WilliamsCite this: J. Phys. Chem. 1994, 98, 31, 7692–7701Publication Date (Print):August 1, 1994Publication History Published online1 May 2002Published inissue 1 August 1994https://doi.org/10.1021/j100082a047RIGHTS & PERMISSIONSArticle Views259Altmetric-Citations21LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (927 KB) Get e-Alerts

Femtosecond optical Kerr effect studies of water

The time-resolved optical Kerr effect of water at 298 K was investigated using pulse widths (full width at half-maximum) as short as 38 fs to characterize the dynamic response of water from tens of femtoseconds to several picosecond time scales. A frequency analysis of the free induction decay of the excited Raman modes observed maxima at 40 and 165 cm[sup [minus]1], with a broad distribution of higher frequency components centered around 470 cm[sup [minus]1]. There is an initial rapid decay in the induced birefringence of less than 50 fs due to interference between these modes. These features are in good agreement with previous depolarized light scattering studies. Additional relaxation components of 500 [+-] 30 fs and 1.7 [+-] 0.3 ps are resolved in the Kerr results. In total, these observations depict an overall dynamic pathway for the relaxation of water. 40 refs., 6 figs.

Resonance-enhanced time-resolved optical Kerr effect of β-carotene in solution

A sharp resonant amplification of the third-order susceptibility of a diluted beta-carotene solution in dodecane is observed by means of the time-resolved optical Kerr effect when the wavelength of the probe is tuned in the range of 490-570 nm. The resonance is well in the red with respect to the 0-0 first electronic transition; some evidence is given of the possible role of higher excited states and of two-photon resonance.

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, CHCl 3, CBrCl 3, CHBr 3 and CFBr 3. 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.

The dynamics of succinonitrile in the plastic phase by subpicosecond time-resolved optical Kerr effect

The relaxation kinetics of succinonitrile in the plastic crystalline phase has been investigated between 250 and 320 K by transient optical Kerr effect with femtosecond pulses. Three different noninstantaneous contributions to the signal time profile have been identified. The fastest one is a subpicosecond decay, attributed to the relaxation of the damped librational and torsional vibrations of the molecules. The intermediate decay time, ranging from 4 ps at 323 K to 30 ps at 250 K, is interpreted as due to rotations of the trans molecules about the shortest inertia axis which bring the molecule from one cube diagonal to another. The slowest decay time ranges from 28 ps at 323 K to 190 ps at 250 K and agrees very well with previous measurements with different experimental techniques. This decay is interpreted as due mostly to rotational motions of the gauche molecules jumping from one equilibrium position to another in the unit cell. The activation energy for the two processes is 3.7 and 4.3 kcal/mol, respectively, for the intermediate and slow kinetics.

Coherent phenomena involved in the time-resolved optical Kerr effect

The effect of parametric coupling between pump and probe beams in time-resolved optical Kerr effect is theoretically discussed for various experimental configurations. It is shown that with a cicularly polarized pump beam, the polarization changes induced on a nearly collinear probe beam are due to this coherence effect only. In other configurations, this parametric coupling can appear as an additional contribution to the observed signal, especially when pump and probe are derived from the same laser beam. It is pointed out that this coupling can occur not only when the pump and probe beams are at the same wavelength, but also when the difference or the sum of their frequencies can excite a Raman or a two-photon resonance in the medium.