Nonlinear absorption, refraction, and optical limiting by a series of monoaxially chloro- and aryl-substituted indium(III) phthalocyanines are described. The absorption cross sections and temporal evolution of the low-lying excited states are also reported. A large nonlinear absorption that increased with wavelength between 500 and 590 nm was observed in each material. The nanosecond nonlinear absorption and the optical limiting are shown to be dominated by a strong excited state absorption from an orientationally averaged triplet state. We derive and experimentally confirm the relation between the molecular absorption cross sections and the fluence-dependent nonlinear absorption coefficients. The effective nonlinear refraction on the nanosecond time scale was reduced because the electronic contribution to the nonlinear refractive index was of the opposite sign from the thermal contribution. An optical limiter using the new material, p-(trifluoromethyl)phenylindium(III) tetra-tert-butylphthalocyanine [(t-...

Effect of Axial Substitution on the Optical Limiting Properties of Indium Phthalocyanines

The contribution of orientational relaxation to the tensor components of the third‐order nonlinear polarization is evaluated for off‐resonance Raman and dipole resonant experiments in the perturbative limit. Orientational correlation functions are calculated within the model of orientational diffusion for all third‐order tensor components relevant to isotropic media. General expressions for polarization geometries that are selective to particular components of the signal, i.e., magic angles, are derived for collinear and crossed‐beam excitation geometries. It is shown that although limited selectivity exists for Raman spectroscopies, no combination of polarizations will give complete selectivity to the isotropic, anisotropic, or nonresonant contributions to the Raman polarizability tensor. For resonant spectroscopies, the four‐time correlation function that describes the orientational polarization decay can be written as the product of three two‐time correlation functions. While magic angles for orientati...

Orientational correlation functions and polarization selectivity for nonlinear spectroscopy of isotropic media. I. Third order

In the optical Kerr effect, the electric field of light incident on a transparent sample induces an anisotropic refractive index, which is measured by its effect on the passage of a second light beam. The advent of lasers powerful enough to generate a measurable effect, and which can be pulsed on femtosecond time scales, has made the optical Kerr effect into a practical technology for investigating the molecular structure and interactions of condensed systems such as pure liquids, liquid solutions, and plastic crystals.

https://science.sciencemag.org/content/sci/262/5138/1386.full.pdf

Ultrafast Optical Kerr Effect in Liquids and Solids

The dynamics of dimethyl sulfoxide (DMSO)/water solutions with a wide range of water concentrations are studied using polarization selective infrared pump-probe experiments, two-dimensional infrared (2D IR) vibrational echo spectroscopy, optical heterodyne detected optical Kerr effect (OHD-OKE) experiments, and IR absorption spectroscopy. Vibrational population relaxation of the OD stretch of dilute HOD in H(2)O displays two vibrational lifetimes even at very low water concentrations that are associated with water-water and water-DMSO hydrogen bonds. The IR absorption spectra also show characteristics of both water-DMSO and water-water hydrogen bonding. Although two populations are observed, water anisotropy decays (orientational relaxation) exhibit single ensemble behavior, indicative of concerted reorientation involving water and DMSO molecules. OHD-OKE experiments, which measure the orientational relaxation of DMSO, reveal that the DMSO orientational relaxation times are the same as orientational relaxation times found for water over a wide range of water concentrations within experimental error. The fact that the reorientation times of water and DMSO are basically the same shows that the reorientation of water is coupled to the reorientation of DMSO itself. These observations are discussed in terms of a jump reorientation model. Frequency-frequency correlation functions determined from the 2D IR experiments on the OD stretch show both fast and slow spectral diffusion. In analogy to bulk water, the fast component is assigned to very local hydrogen bond fluctuations. The slow component, which is similar to the slow water reorientation time at each water concentration, is associated with global hydrogen bond structural randomization.

/pdf/water-dynamics-in-water-dmso-binary-mixtures-31dlxjvetu.pdf

Water dynamics in water/DMSO binary mixtures.

Optical heterodyne-detected optical Kerr effect (OHD-OKE) experiments are used to study the orientational dynamics of the ionic organic liquid 1-ethyl-3-methylimidazolium nitrate (EMIM+NO3−) over time scales from ∼1 ps to ∼2 ns, and the temperatures range from 410 to 295 K. The temperatures cover the normal liquid state and the weakly supercooled state. The orientational dynamics exhibit characteristics typical of normal organic glass-forming liquids. The longest time scale portion of the data decays as a single exponential and obeys the Debye–Stokes–Einstein relation. The decay of the OHD-OKE signal begins (∼1 ps) with a temperature independent power law, t−z, z=1.02±0.05, the “intermediate power law.” The power law decay is followed by a crossover region, modeled as a second power law, the von Schweidler power law. The longest time scale decay is the exponential α relaxation. The intermediate power law decay has been observed in van der Waals supercooled liquids previously. These are the first such obse...

/pdf/orientational-dynamics-of-the-ionic-organic-liquid-1-ethyl-3-2ukyjvksz0.pdf

Orientational dynamics of the ionic organic liquid 1-ethyl-3-methylimidazolium nitrate

We present a subpicosecond time resolved polarization selective transient grating (TG) investigation of pentylcyanobiphenyl (5CB) in its isotropic liquid phase. This system shows complex molecular dynamics with various contributions to the TG signal. With an excitation wavelength λexc=665 nm one induces an anisotropy in the sample from the electronic and nuclear Kerr effects. Exciting with λexc=575 nm generates an excited state grating because of two photon absorption. Solvent relaxation around the excited molecule on a few ps time scale is observed because it spectrally shifts the excited state–excited state transition which is monitored by the TG signal. In addition, radiationless relaxation leads to local heating of the sample in a spatial pattern which mimics the optical interference pattern which established the TG. The heating generates an acoustic standing wave. It is demonstrated that with a single TG setup, polarization selection allows separation and identification of all of the above‐mentioned ...

Analysis of complex molecular dynamics in an organic liquid by polarization selective subpicosecond transient grating experiments

Subpicosecond transient grating optical Kerr effect measurements have been used to evaluate the reorientation of biphenyl molecules in neat biphenyl and n‐heptane solutions. Besides an ultrafast (100 fs time scale) component associated with librational damping/dephasing, two reorientational relaxation components are observed. The slow reorientation is due to rotation around the short axes of the molecule (tumbling motion), the fast reorientation is associated with internal rotation around the central C–C bond and/or rotation of the whole molecule around its long axis (spinning motion). Whereas the tumbling motion has been observed in earlier depolarized light scattering data, the time resolved Kerr data presented here are the first ones to reveal the dynamics of the fast reorientation component and the ultrafast librational dynamics. It is shown that the diffusive reorientational relaxation must be coupled to the ultrafast librational dynamics, and implications of this coupling are pointed out.

Anisotropic reorientational relaxation of biphenyl: Transient grating optical Kerr effect measurements

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 indepen...

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

Tunable subpicosecond pulses are generated by synchronously pumping a dye laser with the pulse-compressed and frequency-doubled output of an acousto-optically mode-locked cw Nd:YAG laser. The pulses are amplified at a repetition rate of 1 kHz, using the frequency-doubled output of a cavity-dumped, acousto-optically mode-locked, Q-switched, cw pumped Nd:YAG laser. Amplified transform-limited pulses of 150–300 fsec have been obtained in the wavelength range of 560–680 nm (R6G and DCM dyes) with a maximum energy of 50 μJ. Since there is no intracavity prism compensation and no recompression stage after the amplifier, the system is tuned easily with a single-plate birefringent filter; only cavity-length adjustment is required. An electronic control system eliminates amplitude fluctuations caused by timing jitter between the 70-psec amplifying pulses and the dye pulses.

/pdf/tunable-subpicosecond-dye-laser-amplified-at-1-khz-by-a-m76anlidh7.pdf

Tunable subpicosecond dye laser amplified at 1 kHz by a cavity-dumped, Q-switched, and mode-locked Nd:YAG laser

Dynamics in the pretransitional isotropic phase of pentylcyanobiphenyl studied with subpicosecond transient grating experiments

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