Third-order nonlinear susceptibilities of several organic solvents are measured by third-harmonic generation at two laser wavelengths: 1.064 and 1.907 pm. The method used allows a determination of the modulus and phase by interference with the harmonic field generated in the liquid-cell windows. Air contribution to the resulting harmonic intensities is studied in detail. An experimental correction for this effect is proposed and verified for some solvents. Results are discussed within the bond-additivity model. tributions from consecutive nonlinear media (S or 3 in our case, depending whether or not we consider harmonic light from air) E (r, t) = g E~" (ri,t)T~, J where TJ are the corresponding whole transmission factors and the resulting harmonic light intensity 2 I "ce(3') J leads to complex interference patterns (cf. Sec. IV).

Analogues of mechanical devices that operate on the molecular level, such as shuttles, brakes, ratchets, turnstiles and unidirectional spinning motors, are current targets of both synthetic chemistry and nanotechnology. These structures are designed to restrict the degrees of freedom of submolecular components such that they can only move with respect to each other in a predetermined manner, ideally under the influence of some external stimuli. Alternating-current (a.c.) electric fields are commonly used to probe electronic structure, but can also change the orientation of molecules (a phenomenon exploited in liquid crystal displays), or interact with large-scale molecular motions, such as the backbone fluctuations of semi-rigid polymers. Here we show that modest a.c. fields can be used to monitor and influence the relative motion within certain rotaxanes, molecules comprising a ring that rotates around a linear 'thread' carrying bulky 'stoppers' at each end. We observe strong birefringence at frequencies that correspond to the rate at which the molecular ring pirouettes about the thread, with the frequency of maximum birefringence, and by inference also the rate of ring pirouetting giving rise to it, changing as the electric field strength is varied. Computer simulations and nuclear magnetic resonance spectroscopy show the ring rotation to be the only dynamic process occurring on a timescale corresponding to the frequency of maximum birefringence, thus confirming that mechanical motion within the rotaxanes can be addressed, and to some extent controlled, by oscillating electric fields.

Magnetism in transition-metal-doped ZnO: A first-principles study J. Appl. Phys. 112, 023913 (2012) Fe3+ doping effects on the structure and multiferroicity of Fe1+xV2−xO4 (0≤x≤0.4) spinels J. Appl. Phys. 111, 124112 (2012) India-stabilized-gadolinia and gadolinia-stabilized-India: Their structural and magnetic properties Optical third harmonic generation measurements by transmission have been performed on thin films of polysilane deposited by a spinning technique with a thickness varying between 0.15 and 0.45 /-Lm. The films have a good optical. quality and support large laser power ( -200 MW /cm 2 at 1.064 /-Lm). They are transparent in visible and near infrared. The measured average value of cubic susceptibility (X~~x ( -3{t); (t),{t),{t)) is equal to (1.5 ± 0.1) X 10-12 esu at 1.064 /-Lm. The technique used for the third harmonic generation measurements allows determination of both modulus and phase of X OI . It is argued that the large value of i 3 ) is due to a three-photon resonance at 1.064 /-Lm.

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A novel organic-inorganic hybrid based on cystamine and BiI5chains is prepared. Due to the flexibility of the disulfide molecules in the structure, single crystals or crystalline thin films of this hybrid undergo a reversible acentric-to-centric structural transition at moderate conditions (T = 36.8 °C). This makes the title compound an excellent candidate for temperature controlled SHG or THG switches.

The permanent all-optical poling of an azo-aromatic acrylic copolymer is experimentally demonstrated by seeding preparation in a backward phase-conjugation geometry. The microscopic mechanism involves an orientational hole burning followed by orientational redistribution caused by trans-to-cis isomerization of the azo-dye chromophores. The characteristic kinetics of monitored by second-harmonic generation.

We report experimenta1 and theoretical investigations of electroabsorption in a polydiacetylene, and determine the complete mechanism of third-harmonic generation (THG) and two-photon absorption (TPA) in linear-chain~-conjugated polymers. The experimental electroabsorption is studied by transmission, rather than reflectance techniques. In addition to the Stark shift of the exciton, a significant feature is observed in the difference spectrum at a higher energy, where the linear absorption is negligible. The origin of this high-energy feature has been controversial. We report several extensive theoretical calculations within the extended Hubbard model, and are able to establish a universality that exists within one-dimensional Coulomb correlated models. We show that the high-energy oscillatory feature in the electroabsorption spectrum originates from the conduction-band threshold, which is separated from the exciton in polydiacetylenes. We also demonstrate that even-parity two-photon states that occur below the one-photon exciton are not observed in electroabsorption due to a cancellation effect. However, a dominant two-photon state that is predicted to occur in between the lowest optical exciton and the conduction-band threshold should be observable. The cancellation, which is only partial for the dominant two-photon state, can, however, reduce the intensity of the resonance due to the state.We show that the conduction-band threshold state, which is an odd-parity one-photon state, also plays an important role in other nonlinear optical processes such as third-harmonic generation and twophoton absorption. Third-order optical nonlinearity in linear-correlated chains is dominated by four essential states: the ground state, the lowest optical exciton and the conduction-band threshold states, and the two-photon state that lies in between the two excited odd-parity states. The two most important predictions of our theoretical work are (a) third-harmonic-generation experiments on ideal isolated strands should find two, not merely one, three-photon resonances, originating from the exciton and the conduction-band threshold states, and (b) only one dominant two-photon resonance in the infinite-chain limit should be observable in THG and TPA. Extensive comparisons between theoretical predictions and experiments are made to prove the validity of the theory. Conjugated polymers other than the polydiacetylenes are discussed briefly.

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