Optical Kerr Effect Measurements Research Articles

Solvent dynamics derived from optical Kerr effect, dielectric dispersion, and time-resolved stokes shift measurements: an empirical comparison

Abstract Data from the optical Kerr effect, time-resolved Stokes shift, and dielectric dispersion experiments on 21 common room temperature solvents are collected and compared. The correlation functions of the collective variables (polarizability, solvation energy, and dipole moment fluctations) responsible for each observable are first extracted from the experimental data and compared directly. In any given solvent the decay times of these various correlation functions are often vastly different. Such differences mainly result from the fact that intermolecular correlations affect the collective variables sampled by each technique in a different manner. To compare dynamics at a more basic level, power law relations are applied in an attempt to account for these correlations and to examine the extent to which the collective dynamics in these three experiments can be viewed as arising from the same underlying single-particle motions (primarily rotations). The Stokes shift and dielectric correlation functions can be reasonably inter-related in this manner, but the polarizability anisotropy monitored with Kerr experiments cannot be as simply related to the former two dynamics, probably due to the importance of collision-induced effects in the latter case.

Influence of Cr capping on the magnetic properties of epitaxial Co on Pd(111)

The influence of Cr deposition on the magnetic properties of epitaxial Co films grown on a Pd(111) single-crystal is analyzed by in situ magneto–optical Kerr effect measurements. Auger electron spectroscopy and low-energy electron diffraction are used for monitoring the growth and structure of the films. Co films thicker than 0.5 monolayer (ML) exhibit a ferromagnetic order at room temperature. In the case of uncovered Co films grown on Pd(111), the easy magnetization axis is found to be perpendicular for thicknesses between 1.1 and 2 ML, and in plane above. Covering thin Co films with Cr layers produces a non-monotonous variation of the coercive field and normalized remanence, and a reorientation of the easy magnetization axis from in plane to out of plane.

Ultrafast Optical Kerr Effect and Solvation Dynamics of Liquid Aniline

Femtosecond optically heterodyne detected optical Kerr effect (OHD-OKE) measurements have been made on liquid aniline. These are contrasted with solvation dynamics measurements made earlier. The OHD-OKE data in the frequency domain can be analyzed in terms of three components: a low-frequency diffusional part; a collisional part; an underdamped intermolecular mode. The latter is quite intense, suggesting strong intermolecular interactions and a relatively high degree of structure in liquid aniline. When the solvation dynamics calculated from the pure liquid data are compared with those measured directly, the agreement beyond 1 ps is good. This result suggests that it is possible to use experimental data obtained on the pure solvent dynamics to model the solvation dynamics response. However, the agreement is not as good at very early times. While this may simply reflect the lower time resolution of solvation dynamics experiments compared to OHD-OKE experiments, we speculate that the differences could also result from either fundamental differences in the measured solvation dynamics and those calculated from OHD-OKE data or a perturbation of the intermolecular interactions in liquid aniline by the solute.

Reorientational and intermolecular dynamics in binary liquid mixtures of hexafluorobenzene and benzene: femtosecond optical Kerr effect measurements

The molecular dynamics of binary liquid mixtures of C 6F 6 and C 6H 6 were studied by using optical heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES) with 45 fs laser pulses at room temperature and ambient pressure. The data give evidence for the effect of interspecies interactions in the short-time, nondiffusive part of the OHD-RIKES response.

Properties of rare-earth—transition-metal sandwich films

In sandwich systems made by stacking coupled layers with typical thicknesses 100 nm, a specific type of domain wall may be found. This extends over the whole film surface and is termed the extended domain wall (EDW). As a result, peculiar magnetisation processes are observed, some typical examples of which are described in this paper. The formation of EDWs occurs by nucleation/propagation. Experimental evidence for the existence of EDWs is obtained from optical Kerr effect measurements. Magnetization processes are described in both analytical and numerical approaches. High susceptibility in low fields and large magnetostriction anomalies may occur in these systems.

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.

LOW FREQUENCY MODES PROBED BY TIME-DOMAIN OPTICAL KERR EFFECT SPECTROSCOPY

The principle and application of ultrafast optical Kerr effect (OKE) spectroscopy have been reviewed. This spectroscopy is shown to be very useful to investigate low frequency modes in disordered materials and the obtained data are directly comparable with frequency-domain light scattering spectroscopy. Experimental study to show the consistency between the time- and frequency-domain spectroscopy has been performed for liquid nitrobenzene and the excellent agreement is attained over three orders of magnitude in frequency range. It is also shown that the result obtained by the OKE measurement is consistent with that obtained by four wave mixing spectroscopy. Combination of these spectroscopic techniques is particularly suited for the investigation of low frequency modes because a wide frequency range is covered with great accuracy. Several remarks concerning the OKE spectroscopy are presented such as the breakdown of Debye relaxation model and various interference effects which may distort the time-domain data.

Interrogation of Vibrational Structure and Line Broadening of Liquid Water by Raman-Induced Kerr Effect Measurements within the Multimode Brownian Oscillator Model

The method used to deduce the spectral density distribution of intermolecular and intramolecular (vibrational) degrees of freedom in the liquid state from optical heterodyne detected optical (Raman-induced) Kerr effect (OHD-RIKE) measurements is reexamined within a multimode Brownian oscillator model. The ramifications of nonlinear coupling of the nuclear degrees of freedom to the medium polarizability are explored for discrimination between “homogeneous” and “inhomogeneous” contributions to the vibrational spectral density. Under physically reasonable assumptions, an estimation of the homogeneous contribution to the vibrational line shape can be made from the OHD-RIKE observable (if nonlinear coupling is nonnegligible). The model is developed generally, and calculations are applied specifically to temperature-dependent OHD-RIKE measurements of liquid water. The results indicate that the line broadening in the low-frequency vibrational distribution due to the hydrogen-bonded network structure of liquid wa...

The solvent spectral density and vibrational multimode approach to optical dephasing: Two-pulse photon echo response

A rigorous theoretical connection between the polarizability spectral density obtained from optical Kerr effect (OKE) measurement with the correlation function describing solvent-induced optical dephasing detected in photon echo measurements is given. The experimentally obtained spectral density has a more reasonable physical basis than model correlation function descriptions of solvent fluctuations. The experimental OKE spectrum is demonstrated to provide a natural description of solvent motions that modulate the chromophore electronic states in the case of weak induced-dipolar interactions. The chromophore optically active vibrational modes are obtained from pump-probe spectra and are employed in the calculation of echo signals. It is found that the fast decays of the two-pulse echo signals result from both solvent and solute intramolecular motions while the echo peak shifts are dominated by the solvent intermolecular modes.

Direct comparison between femtosecond optical Kerr effect and high-resolution light scattering measurements

We have performed optically heterodyne-detected optical Kerr effect measurement for transparent liquids with ultrashort light pulses. In addition, the depolarized low-frequency light scattering measurement has been performed by means of a double monochromator and a high-resolution Sandercock-type tandem Fabry-Perot interferometer. The frequency response functions obtained from the both data have been directly compared. They agree perfectly for a wide frequency range. This results is the first experimentaa evidence for the equivalence between the time- and frequency-domain measurements.

Complex dynamics and the stimulated gain spectrum of pentylcyanobiphenyl in the isotropic phase

We have measured high resolution polarized and depolarized stimulated gain spectra of the liquid crystal pentylcyanobiphenyl (5CB) in its isotropic phase between 36.2 and 122°C. Spectral features associated with slow collective reorientation, acoustic waves (Brillouin peaks), and rapid anisotropy fluctuations are all present and can be simultaneously measured with high resolution in a single spectrum. Our results for both the slow and intermediate timescale reoirientational dynamics are in good agreement with recent transient-grating optical Kerr effect measurements on 5CB.

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

Ultrafast nonexponential dynamics in a polymer glass forming liquid

The orientational dynamics of phenyl side groups in poly(methylphenylsiloxane) (PMPS) melts are examined over a broad range of viscosity/temperature (η/T) using subpicosecond transient grating optical Kerr effect (TGOKE) measurements. Measurements on poly(dimethylsiloxane) are also reported. Following ultrafast (hundreds) of fs librational dynamics, the phenyl side group orientational dynamics occur over a range of times from 2 ps to a few hundred ps. The experiments were performed from 25 to 143 °C, resulting in η/T changing by a factor of 40. In spite of the large change in η/T, the side group dynamics remain unchanged throughout the entire temperature range. Comparison of the dynamics of PMPS in the melt and PMPS in dilute CCl4 solution shows that chain–chain interactions influence the phenyl side group dynamics in the melt. The dynamics are described as local orientational relaxation of phenyl groups in the microenvironments defined by the backbone geometry and side group steric interactions rather than rotational diffusion. The dynamics exhibit power-law behavior, t−α, over two decades of signal decay. Two possible physical processes that can give rise to a power-law decay are discussed. The relationship of the observed dynamics to the β and α relaxations of glass forming liquids is also discussed.

The development of organic third-order nonlinear optical materials.

Third-order nonlinearities of the solutions of various organic molecules are evaluated by the measurement of optical Kerr effect near the absorption edge of each compound, varying the wavelength of nanosecond laser. Aromatic acetylenes, imidazoles, organic donors or acceptors used for organic conductive compounds, organo-metallic complexes, cyanine dyes, azo dyes, helicenes, and the other π-conjugated compounds are measured. From the results, aromatic acetylenes, imidazoles, and cyanine dyes are selected as the compounds with the large χ(3) values.

Ultrafast side group motions of polymers

The local dynamics of poly(2-vinylnaphthalene) (P2VN) have been investigated using femtosecond transient grating optical Kerr effect measurements. In solid P2VN, a single exponential 140-fs decay is observed. This decay is attributed to librational relaxation of the naphthyl side groups. In P2VN/CCl 4 solution, besides the librational decay, there exist two slower orientational relaxation components. These decays are temperature independent in the range -3 to +55 o C, although the bulk sheer viscosity of the solution and the viscosity of pure CCl 4 change considerably

Femtosecond intermolecular vibrational motion in pyrrole

Femtosecond optical Kerr effect measurements were performed on neat pyrrole, neat deuterated pyrrole- d 5 and mixtures with ethyl-ether. Underdamped oscillatory motion is observed that is shown to be due to intermolecular vibration of pyrrole dimers.

Ultrafast solvent dynamics: Connection between time resolved fluorescence and optical Kerr measurements

The vibrational characteristics of liquid dynamics are used to describe the ultrafast relaxations observed in time-dependent fluorescence Stokes shift [J. Chem. Phys. 95, 4715 (1991)] and heterodyne detected optical Kerr effect measurements on acetonitrile, via a Brownian oscillator model. Introducing a frequency distribution of vibrational modes makes it possible to compare the two experiments. The ultrafast decays observed in the fluorescence Stokes shift and optical Kerr signals are produced by destructive superposition of the high frequency, underdamped modes.

Nonhydrodynamic molecular motions in a complex liquid: Temperature dependent dynamics in pentylcyanobiphenyl

The isotropic phase of nematogenic substances above the nematic–isotropic phase transition temperature Tni is characterized by short range orientational correlation of the molecules and the existence of pseudonematic domains. This microscopic structure has a strong influence on reorientational dynamics in the liquid. We present time resolved transient grating optical Kerr effect measurements of pentylcyanobiphenyl between 35 and 120 °C, which allow us to monitor dynamics on timescales from subpicoseconds to tens of nanoseconds. The well-known collective component characterizing the reorientational dynamics of the pseudonematic domains follows Landau–deGennes behavior up to 30–35 degrees above Tni where the theoretical correlation length ξ≊three molecular lengths. Additionally fast relaxation channels (with time constants between 1 and 300 ps) are observed which are associated with local reorientational and intermolecular dynamics within the pseudonematic domains. The local dynamics are temperature independent in the range where the pseudonematic domains dominate the liquid structure, demonstrating a decoupling of the molecular motions from the bulk viscosity. Only at high temperatures, T≳70 °C, where the pseudonematic domains cease to exist, is a viscosity dependence observed. At these elevated temperatures, the slowest contribution to the fast molecular dynamics approximately follows hydrodynamic theory.

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