A. F. Garito

Superconducting fluctuations and the Peierls instability in an organic solid

Abstract The discovery of extraordinary conductivity maxima in a class of organic charge transfer salts is reported. The data are interpreted as resulting from superconducting fluctuations at high temperatures. A possible mechanism for achieving high temperature superconductivity is suggested based on the electron-phonon interaction, in the strong-coupling limit, and the Peierls soft-mode instability in pseudo-one-dimensional systems. Procedures are suggested for the possible eventual stabilization of the superconducting state.

Measurements of molecular second order optical susceptibilities using dc induced second harmonic generation

We have developed an infinite dilution extrapolation procedure for determining the molecular second order optical susceptibility β using dc induced second harmonic generation. We show how the effects of solute–solute and solvent–solvent interactions are minimized by this procedure, and how several local field models used in the procedure affect the calculation of β. Using hexane as a solvent for nitrobenzene, we have determined the best experimental value in solution for the intrinsic β of nitrobenzene of (1.11±0.17)×10−30 esu.

An exceptionally large linear electro‐optic effect in the organic solid MNA

The dc linear electro‐optic effect and the x‐ray crystal structure of the organic molecular solid 2‐methyl‐4‐nitroaniline (MNA) have been studied. Of two crystal orientations measured, one polar orientation was found to have an exceptionally large figure of merit for electro‐optic phase retardation, comparable to that of LiNbO3. Comparison with second harmonic generation results demonstrates that the linear electro‐optic effect in MNA is primarily electronic in nature. The origin of the large macroscopic second order nonlinear optical susceptibility is traced to a single large component of the corresponding microscopic molecular susceptibility.

Electrical conductivity of (SN)x

Abstract Measurements of the b -axis conductivity of polymeric sulfur nitride (SN) x from 4.2–300K are reported for samples having different polymerization times. A general increase in the conductivity was found with longer polymerization times leading to room temperature conductivities 1200–3700 (Ω-cm) −1 and resistance ratios 50–205. The temperature dependence of the resistivity can be represented by Matthiessens rule showing the intrinsic resistivity over a broad temperature range 15 T T 2 form which is discussed in terms of electron-electron scattering.

Rare-earth organic complexes for amplification in polymer optical fibers and waveguides

The optical properties of rare-earth organic complexes have been studied because of their possible application to polymer optical fibers and waveguides. Er3+, Nd3+, and Sm3+ ions are encapsulated in tetrakis(benzoyltrifluoroacetonate) and tetrakis(dibenzoylmethide) chelates, and their radiative properties are evaluated in several organic solvents. Analysis reveals that tetrakis(benzoyltrifluoroacetonate) chelates are promising dopants for use in rare-earth-doped polymer devices. These rare-earth complexes can be doped to high concentrations in polymer systems without quenching, providing the means for short-length amplification devices. Numerical simulations reveal that gains as high as and exceeding 20 dB should be realizable in rare-earth-doped polymer fiber amplifiers having lengths <60 cm. Similar calculations reveal threshold pump powers of tens of milliwatts for rare-earth-doped polymer fiber lasers.

Molecular Optics: Nonlinear Optical Processes in Organic and Polymer Crystals

Abstract Physical studies of nonlinear optical properties of organic and polymer structures have demonstrated exceptionally large second and third order nonlinear optical responses that are important to the fields of nonlinear optics and optical device technologies. These unusual responses have been exhibited by a large number of structures, phases, and states that include organic solids and films, single crystal polymers, Langmuir-Blodgett films, liquid crystals, and liquid crystal polymers. Experimental and theoretical studies of such systems have achieved significant advances in the understanding of these exceptional macroscopic nonlinear optical responses based on theoretically calculated microscopic electronic mechanisms, especially the role of electron-electron correlations and highly charge correlated electron excited states. Combined theory and experiment has led to the recent discovery of liquid crystal polymerization of divinyldiacetylene monomers to form highly conjugated liquid crystal polymer...

‘Organic metals’: alkylthio substitution effects in tetrathiafulvalene–tetracyanoquinodimethane charge-transfer complexes

The synthesis and diverse conductivity properties of the tetracyanoquinodimethane (TCNQ) complexes of several tetrakis-(alkylthio)-tetrathiafulvalenes are described, and compared with those of tetrathiafulvalene-TCNQ and related complexes.

Nonlinear-optical processes in lower-dimensional conjugated structures

Reduced dimensionality and quantum confinement in conjugated organic and polymer structures enhance the effects of electron correlation on virtual electronic excitation processes and nonlinear-optical responses. A microscopic many-electron description of the third-order susceptibilities γijkl(−ω4; ω1, ω2, ω3) of conjugated structures is reviewed for one-dimensional chains and extended to two-dimensional conjugated cyclic structures. Electron correlation effects in effectively reduced dimensions result in highly correlated π-electron virtual excitations that lead to large, ultrafast nonresonant nonlinear-optical responses. The increase of dimensionality from linear to cyclic chains is found to reduce the nonresonant isotropic third-order susceptibility γg. Resonant experimental studies of saturable absorption and optical bistability in ultrathin films of quasi-two-dimensional naphthalocyanine oligomers are also presented. In the saturable-absorption studies, the resonant nonlinear refractive index n2 was measured to be 1 × 10−4 cm2/kW in the wavelength range of operating laser diodes. Based on this result, electronic absorptive optical bistability is observed on a nanosecond time scale in a nonlinear Fabry–Perot interferometer employing the saturably absorbing naphthalocyanine film as the nonlinear-optical medium.

Epitaxial Growth of Organic Thin Films by Organic Molecular Beam Epitaxy

Epitaxial growth of an organic ultrathin film has been confirmed for the first time by reflection high-energy electron diffraction (RHEED) during film growth. Copper phthalocyanine (CuPc) films were grown heteroepitaxially on a cleaved face of MoS2 under high vacuum of ca. 4×10-9 torr by a newly developed organic molecular beam epitaxy technique. The RHEED pattern revealed that epitaxially grown CuPc has its own lattice constant, which is completely different from that of MoS2 even at the initial deposition stage.

Phases and Third-Order Optical Nonlinearities in Tetravalent Metallophthalocyanine Thin Films

The third-order optical susceptibilities χ1111(3)(-3ω; ω, ω, ω)sfortwodifferentphasesinvanadylandtitanylphthalocyanine (VOPcandTiOPc) vacuum-depositedthinfilmsaredeterminedbyopticalthird-harmonicgeneration (THG) measurementsatwavelengths 1543 nmand 1907 nm. Thermalannealingcausesaphasetransitionwhichaccompaniesaredshiftintheirabsorptionspectraandanincreaseinthe χ^(3) valueof 2-5 timesinVOPcandTiOPcfilms. Theenhancementofthethird-orderopticalnonlinearitiesintetravalentphthalocyaninefilmsisdiscussedintermsofmolecularpacking.