Time-resolved Optical Kerr Effect Research Articles

Conductivity and optical nonlinearity of Sb doped SnO 2 films

The conductive Sb doped tin oxide films on the SiO 2 substrate were prepared by r.f. sputtering. The dc conductivity and the third-order optical nonlinear susceptibility of Sb:SnO 2 films with the Sb doped atomic content in the range of 1.3∼39.2 at.% were investigated. The value of χ (3) varies in the range of 1.1 × 10 − 10 ∼1.7 × 10 − 10 esu with different Sb doped content, which were measured via a time-resolved optical Kerr effect technique using femtosecond laser pulses at 830 nm.

Time-resolved optical Kerr-effect investigation on CS2/polystyrene mixtures

The relaxation dynamics of carbon disulfide are investigated in mixtures with polystyrene (PS) using the time-resolved optical heterodyne-detected optical Kerr effect (OHD-OKE). The data are analyzed using both the model-dependent approach, which assumes four distinct temporal responses, and the model-independent Fourier transform approach, which generates a spectral response that can be compared with results obtained by depolarized Rayleigh scattering. A slow dynamics is observed for the OHD-OKE transient decaying exponentially with a time constant that varies from 1.68 ps for neat CS2 to 3.76 ps for the most concentrated CS2PS mixture. The increase of this time constant accompanies an increase in the viscosity of the mixture, so we can associate this component with the diffusive reorientation process of the induced polarizability anisotropy of the carbon disulfide in the mixture. The short-time nuclear response is characterized in the frequency domain by a broad band that peaks around 30 cm(-1) for neat carbon disulfide, and is associated with a complex relaxation pattern. The vibrational distribution shifts to higher frequencies when the PS concentration is increased in the mixture. This result is discussed in terms of an increase in the interaction strength between the PS phenyl rings and the carbon disulfide molecules.

Structure dependence of ultrafast third-order optical nonlinearity for Ge–Ga–Cd sulfide glasses

Ultrafast third-order nonlinear optical responses of GeS2?Ga2S3?CdS glasses have been measured by using femtosecond time-resolved optical Kerr effect (OKE) technique at the wavelengths of 820nm and 640nm respectively. The experimental results show that GeS2?Ga2S3?CdS glasses have large femtosecond third-order optical nonlinear responses and their OKE signals vary considerably with the composition. The relationship of structure-property is discussed by means of Raman spectroscopy analysis, suggesting that the tetrahedron unit [GeS4] or [GaS4] plays an important role in the ultrafast third-order nonlinear optical response. In addition, the experimental results also reveal that the ultrafast third-order optical nonlinearity of these glasses does not obey the Miller rule.

Off-Resonant Third-Order Optical Nonlinearity of an Ag:TiO2Composite Film

Using the femtosecond time-resolved optical Kerr effect technique, weinvestigate the off-resonant nonlinear optical response of anAg:TiO2 composite film prepared by a vacuum magnetron sputteringmethod. The third-order nonlinear optical susceptibility of thecomposite film with silver nanoparticle size of about 30 nm isestimated to be 1.9×10−10 esu at the incident laser wavelength of800 nm. When the photon energy of the incident beam is lower than thatfor surface plasmon or the interband transition of silvernanoparticles, the observed third-order optical nonlinearity isattributed to the intraband transition of the free electrons. Based onthe linear limit of the electric field within micro-spherical model, weassign this large optical nonlinearity to the local field enhancementof the third-order nonlinearity.

Ultrafast Dynamics in the Dispersed Phase of Oil-In-Water Microemulsions: Monosubstituted Benzenes Incorporated into Dodecyltrimethylammonium Bromide (DTAB) Aqueous Micelles

Time-resolved optical Kerr effect spectroscopy has been used to probe the molecular environment afforded by the hydrophobic core of oil-in-water microemulsions. This was achieved by measuring the ultrafast dynamics of a series of benzene derivatives (benzonitrile, nitrobenzene, fluorobenzene, styrene, and toluene) incorporated as the oil phase within oil-in-water microemulsions and comparing them to the dynamics in neat liquid and the liquid diluted in nonpolar solvent. Polar and strongly interacting liquids (benzonitrile and nitrobenzene) showed dynamics in the microemulsion that are similar to those in the solution phase, while weakly interacting and mildly polar liquids (fluorobenzene, styrene and toluene) reveal dynamics more similar to those of the neat liquid. This suggests stabilization of the polar dispersed phase in polar regions of the micelle.

Annealing effect of linear and nonlinear optical properties of Ag:Bi2O3 nanocomposite films

Silver nanoparticle/bismuth oxide composite films were deposited by cosputtering and annealed at different temperatures. The X-ray diffraction results demonstrate that the silver and bismuth oxide were well crystallized after 600 degrees C thermal annealing. The linear absorption peaks show a red-shift behavior while increasing annealing temperature. The annealing effect of the third-order nonlinear optical susceptibilities and ultrafast nonlinear optical response of the silver nanoparticles/bismuth oxide composite thin films are investigated using the femtosecond time-resolved optical Kerr effect technique under 800 nm wavelength. The maximum value of chi(3) of Ag:Bi2O3 thin films is 2.1X10 esu, which occurs at an annealing temperature of 600 degrees C. The ultrafast optical response spectra demonstrate the temperature dependence of decay process time.

Ultrafast third-order optical nonlinearity of polycyanopyridine

A novel plasma-polymerized 4-cyanopyridine (PP4CPD) thin film of desired thickness was prepared by plasma polymerization under different glow discharge conditions. The effect of the discharge power on the chemical structure and surface compositions of the PP4CPD films was investigated by FT-IR, UV–Vis and X-ray photoelectron spectroscopy (XPS). A high retention of the aromatic ring structure of the starting monomer in the deposited plasma films is obtained at a low discharge power. A red shift in the maximum absorption wavelength ( λ max) for PP4CPD films was observed as compared with the monomer absorption spectrum. The atomic force microscopy (AFM) measurement shows that the PP4CPD film with quite a smooth surface could be grown under a relatively low discharge power. A femtosecond time-resolved optical Kerr effect (OKE) technique has been applied to investigate the third-order nonlinearity of the plasma PP4CPD film. For the first time, a non-resonant optical Kerr effect and ultrafast response of polycyanopyridine was observed.

Structural Relaxation in Supercooled Water by Time‐Resolved Spectroscopy.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Time-resolved optical Kerr effect experiments on supercooled benzene and test of mode-coupling theory

We have performed time-resolved optical Kerr effect experiments with heterodyne detection on benzene. We succeeded in supercooling benzene by 21 K below the melting point T m = 279 K, and we investigated the full range of existence from the supercooled phase up to the boiling point T b = 353 K. Our time-resolved data show clearly the complex relaxation pattern of benzene that is characterized by different time scales. These dynamic features, common to many other molecular liquids, to date have not been addressed and there is not a unique theoretical model able to explain them, even in a simple molecular liquid such as benzene. We compare our data with the predictions of a schematic mode-coupling model, fitting the experimental relaxations with a numerical solution of the time-dependent correlation functions. Although the temperature range investigated is clearly outside the asymptotic scaling regime, we found the mode-coupling model able to describe properly the measured dynamics in large time and temperature ranges.

Structural relaxation in supercooled water by time-resolved spectroscopy.

Water has many kinetic and thermodynamic properties that exhibit an anomalous dependence on temperature, in particular in the supercooled phase. These anomalies have long been interpreted in terms of underlying structural causes, and their experimental characterization points to the existence of a singularity at a temperature of about 225 K. Further insights into the nature and origin of this singularity might be gained by completely characterizing the structural relaxation in supercooled water. But until now, such a characterization has only been realized in simulations that agree with the predictions of simple mode-coupling theory; unambiguous experimental support for this surprising conclusion is, however, not yet available. Here we report time-resolved optical Kerr effect measurements that unambiguously demonstrate that the structural relaxation of liquid and weakly supercooled water follows the behaviour predicted by simple mode-coupling theory. Our findings thus support the interpretation of the singularity as a purely dynamical transition. That is, the anomalous behaviour of weakly supercooled water can be explained using a fully dynamic model and without needing to invoke a thermodynamic origin. In this regard, water behaves like many other, normal molecular liquids that are fragile glass-formers.

Linear and ultrafast nonlinear optical response of Ag:Bi2O3 composite films

Silver/bismuth oxide composite thin films with Ag concentration varying from 13.2% to 59.3% were prepared by cosputtering in a multitarget magnetron sputtering system. The absorption spectra of these thin films were measured, and the absorption peaks due to surface plasmon resonance of Ag particles showed a redshift behavior with increasing Ag concentration. By using the femtosecond time-resolved optical Kerr effect technique under 800 nm wavelength, the nonlinear optical properties of these films were investigated. The Kerr signals showed an ultrafast rise, suggesting that the main physical mechanism involved in the optical nonlinearity of Ag:Bi2O3 thin films on the femtosecond scale was the pure electronic contributions. The maximum value of the third-order nonlinear optical susceptibility of Ag:Bi2O3 thin films was 4.1×10−10 esu, and occurred at a Ag concentration of about 35.7%.

The effects of anion and cation substitution on the ultrafast solvent dynamics of ionic liquids: A time-resolved optical Kerr-effect spectroscopic study

Ultrafast solvent dynamics of room-temperature ionic liquids have been investigated by optical heterodyne-detected Raman-induced Kerr-effect spectroscopy (OHD-RIKES) by studying the effects of cation and anion substitution on the low frequency librational modes. The spectra of two series of imidazolium salts are presented. The first series is based on the 1-butyl-3-methylimidazolium salts [bmim]+ containing the anions trifluoromethanesulfate [TfO]−, bis(trifluoromethanesulfonyl)imide [Tf2N]−, and hexafluorophosphate [PF6]−. The second series is based on [Tf2N]− salts containing the three cations 1-butyl-2,3-dimethylimidazolium [bmmim]+, 1-methyl-3-octylimidazolium [omim]+, and [bmim]+. It is found in all five samples that the signal is due to libration of the imidazolium ring at three frequencies around 30, 65, and 100 cm−1 corresponding to three local configurations of the anion with respect to the cation.

Third-order nonlinear optical response of Au-core CdS-shell composite nanoparticles embedded in BaTiO 3 thin films

Au-core CdS-shell composite nanoparticles were synthesized by a direct self-assembly process and integrated into BaTiO3 thin films. Characterization by transmission electron microscopy showed that the average diameter of these composite nanoparticles was about 8 nm. Using the femtosecond time-resolved optical Kerr effect method, we investigated the third-order nonlinear optical response of the Au@CdS nanoparticles embedded in the BaTiO3 thin films at a wavelength of 800 nm. An ultrafast nonlinear response and a large effective third-order nonlinear susceptibility of χ(3)=7.7×10-11 esu were observed. We attributed the enhancement of the third-order optical nonlinearity to a localized electric field effect originating from the core-shell structure under off-surface-plasmon resonance conditions.

Experimental studies of the ortho-toluidine glass transition.

The thermodynamic and dynamics proprieties of ortho-toluidine, in the vicinity of a glass transition, have been studied by calorimetric and by two light scattering techniques, depolarized light scattering and time-resolved optical Kerr effect. Differential scanning microcalorimetry clearly detects a glass transition in o-toluidine and it measures some thermodynamics critical parameters, in particular, the transition temperature. The light scattering data have been analyzed according to the mode-coupling theory. This theory gives a good interpretation of our data and it allows to extract safely the critical parameters of the o-toluidine dynamics. We found a fair agreement between the analysis outputs performed in the frequency domain and in the time domain. Finally, we compared the glass transition features of o-toluidine with that of its isomer meta-toluidine, looking for some general idea about the molecular aspects of the glass transition.

Time-resolved optical Kerr-effect spectroscopy of low-frequency dynamics in Di-L-alanine, poly-L-alanine, and lysozyme in solution.

The low-frequency spectra of peptides and proteins in solution have been investigated with optical heterodyne-detected Raman-induced Kerr-effect spectroscopy. Spectra were obtained for di-l-alanine ALA(2) and poly-l-alanine (PLA) in dichloroacetic acid solution. The conformational dependence of those spectra at low frequency has been analyzed. ALA(2) displays a band centered at 50 cm-1, whereas the alpha-helical PLA shows two shoulders at 60 and 140 cm-1. The similarity of the spectral features observed in PLA to those in water can be explained by analogous acoustic translational modes in the hydrogen network of the PLA alpha-helix. The mostly alpha-helical protein lysozyme in aqueous solution has also been investigated and showed significantly more structure with modes at 10, 35, 73, 106, and 164 cm-1.

Rotational Friction Kernel in Water from the Femtosecond Time-Resolved Optical Kerr Effect of Acetonitrile/Water Mixtures

Depolarized Rayleigh scattering (DRS) of acetonitrile/water mixtures is examined with the time-resolved, heterodyne-detected optical Kerr effect (OHD-OKE). For neat water, the rise of electronic response gives a symmetricapparatus function and an asymmetric correction is constructed with the help of high-frequency Raman data. For the mixtures at 21 °C, depolarized Raman spectra up to 1600 cm - 1 are obtained with high signal/noise ratio. The DRS spectra for acetonitrile mole fraction 0.05 ≤ x A C N ≤ 1 are decomposed into the spectra of water and of neat acetonitrile and a composite spectrum with associated weight functions. The spectral density at infinite dilution in water is obtained by extrapolation and transformed into the second-rank orientational correlation function of single acetonitrile solutes. The Einstein frequency of 31.11 cm - 1 is higher than the value of 27.11 cm - 1 for the potential-free stochastic rotor and an oscillation is observed in the corresponding velocity correlation function, both indicating librational motion in a solvent cage. The rotational correlation time τ 2 = 1.49 + 0.015 ps may be used to rescale τ 2 values from 1 4 N nuclear quadrupole relaxation in water; the comparison provides an improved value 4.54 ′ 0.03 MHz for the coupling constant. The correlation function is inverted to give the kernel for rotational friction. The latter consists of a fast biexponential decay with a 33-fs correlation time followed by exponential decay with a 0.779-ps time constant. An oscillatory residue around 0.3 ps indicates coupling between acetonitrile libration and the water frictional modes.

Relaxation processes in an epoxy resin studied by time-resolved optical Kerr effect.

The dynamics of the epoxy resin phenyl glycidyl ether, a fragile glass-forming liquid, is investigated in the liquid and supercooled phases by time-resolved optical Kerr effect experiment with an heterodyne detection technique. We tested the mode-coupling theory and found that the predicted dynamic scenario allows to reproduce properly the measured signal, for t>1 ps, in the whole temperature interval investigated. Furthermore, the values of T(c) and lambda, obtained from the analysis of three different and independent dynamic regimes (alpha regime, von Schweidler, beta regime), are in remarkable agreement. Moreover, relaxation times obtained from optical Kerr effect and dielectric spectroscopy measurements are compared. The two time scales differ only for a constant factor in the whole temperature interval investigated.

Nanostructured Silver/Polystyrene Composite Film: Preparation and Ultrafast Third-Order Optical Nonlinearity

Surface-modified silver nanoparticles with various sizes, synthesized by water-in-oil micro-emulsion, were incorporated into polystyrene (PS) to form transparent nanocomposite films through solution-mixing and static-casting. It was found that the Ag nanoparticles could be re-dispersed well in the polymer matrix by using chloroform as a solvent due to a strong interaction between Ag and chloroform. XPS analysis suggested that there is no obvious interaction between nanosilver and the polystyrene matrix. The third-order nonlinear optical susceptibility of Ag/PS nanocomposite films is around 10-esu and increases with increasing particle size, as measured by the time-resolved femtosecond optical Kerr effect experiment at a wavelength of 830nm. The results demonstrate that the present fabrication approach can effectively tailor the structure and properties of the nanocomposites.

Temperature dependence of low-frequency responses of liquid 1-alkenes studied by femtosecond optical Kerr effect spectroscopy

Femtosecond time-resolved optical Kerr effect measurements have been performed in three 1-alkene liquids in order to investigate the low-frequency responses in a wide range of temperature, 50 ∼ 290 K, 133 ∼ 290 K and 153 ∼ 290 K for 1-pentene, 1-hexene and 1-heptene, respectively. It has been found that the low-frequency responses of three liquids have two frequency regions where the spectral low-frequency show strong temperature dependence. One is the low frequency part less than several 10 cm −1, which includes the relaxational mode in a very low frequency range. The other is the intramolecular Raman band around 100 cm −1. The origin of the temperature dependence is discussed with the model which consists of anharmonically coupled oscillators.

Fast dynamics of a fragile glass former by time-resolved spectroscopy

Abstract We measured the dynamics of the fragile glass former m-toluidine in its supercooled phase by the time-resolved optical Kerr effect. Using an experimental time filtering of the internal molecular vibrations a better insight into the fast relaxation processes has been achieved. We analysed the dynamic features of these fast processes and compared them with the mode-coupling theory predictions.