Steven R. Flom

Indium phthalocyanines and naphthalocyanines for optical limiting

Abstract In this work, an overview of optical limiting processes in phthalocyanines is given. The synthesis and the linear and nonlinear optical properties of a series of highly soluble axially substituted indium(III) phthalocyanines and the analogous series of naphthalocyanines are described. Several techniques, such as transient absorption, Z-scan, and degenerate four-wave mixing (DFWM), were used for assessing the optical properties and optical limiting performance of the indium phthalo- and naphthalocyanines.

Large third‐order optical nonlinearities in organic polymer superlattices

Large second hyperpolarizabilities, 〈γxxxx〉, have been measured in solutions of two recently prepared organic polymer superlattices. These compounds have period aromatic and quinoidal structures and differ from each other by a side group substituent. The values observed are 1.6×10−29 esu for the parent copolymer and 3.7×10−30 esu for its acetoxy derivative. The corresponding values of χ(3)xxxx for the solid phase are estimated to be 2.7×10 −7 and 4.5×10−8 esu. Time‐resolved degenerate four‐wave mixing measurements, made at 532 nm, showed that the dynamics of the parent copolymer were faster than the 25 ps resolution of the instrument while the derivative exhibited an additional slower response component.

Third‐order nonlinear optical properties of a soluble conjugated polythiophene derivative

The second hyperpolarizability 〈γxxxx 〉 of a new, soluble, conjugated polythiophene derivative, containing aromatic and quinoid moieties, is measured to be 1.2×10−31 esu. The measurement was made at 532 nm in a dichloromethane solution by picosecond‐resolved degenerate four wave mixing. The corresponding macroscopic third‐order susceptibility χ(3 ) is estimated to be 4.6×10−9 esu, which is larger than that of the parent poly(2,5‐thiophene) and many currently known nonlinear optical polymers.

The photodynamics of 2-(2′-hydroxy-5′-methylphenyl)-benzotriazole in low-temperature organic glasses

Abstract The non-time-resolved and time-resolved emission spectroscopy of 2-(2′-hydroxy-5′-methylphenyl)-benzotriazole in low-temperature organic glasses has been investigated. The observed data are consistent with a kinetic model that has been discussed previously by several researchers. Our results suggest that the extremely efficient electronic radiationless decay of this compounds is due to an exceptionally rapid decay rate for the proton-transferred form of the first electronically excited singlet state.

Synthesis, aggregation behavior and nonlinear absorption properties of lead phthalocyanines substituted with siloxane chains

The synthesis and characterization of polysiloxane substituted metal-free and lead phthalocyanines are described. These materials form a class of isotropic liquid phthalocyanines that combine a large nonlinear absorption with an exceptionally large nonlinear thermal refractive effect. These materials effectively couple the nonlinear absorption characteristics of the phthalocyanine (Pc) moiety with the thermorefractive properties typical of siloxanes. The room temperature index of these phthalocyanines can be varied by the choice of the siloxane substituent. Furthermore, the siloxane substituents are effective at inhibiting aggregation of the phthalocyanine rings. The observed aggregation constants in toluene solutions are very small and only a small degree of aggregation is observed even in the pure liquid phthalocyanines. Nonlinear transmission, z-scan, transient absorption and degenerate four-wave mixing studies confirm that the Pb substituted materials possess a broad spectral region of induced absorption with nonlinear absorption coefficients similar to that observed from other lead substituted phthalocyanines. The observed ground state molar absorption coefficients of the siloxy phthalocyanines are somewhat smaller than comparable alkyl substituted phthalocyanines. Taken together, these properties make these materials very useful for practical nonlinear optical applications. The coupling of siloxane chains to the Pc rings represents a promising way to achieve some important properties that are difficult to achieve by other means.

Lead phthalocyanine reverse saturable absorption optical limiters

Systematic studies of the nonlinear optical properties of organic materials have led to the development of promising new materials for optical limiting. Several heavy metal substituted phthalocyanines are effective materials for optical limiters in the visible and near IR. Nonlinear absorption is the principal mechanism near the limiting threshold. In fast optical systems, refractive contributions also contribute at higher energies. These refractive contributions are predominantly thermal. The spectral window over which the limiter operates can be engineered by altering both the main ring and peripheral substitution of the molecules.

Picosecond time-resolved emission spectra: techniques and examples

Abstract This paper describes a laser spectrometer that yields picosecond time-gated emission spectra which are characterized by a high signal-to-noise ratio and a broad spectral coverage. The crucial experimental methods are presented, with particular emphasis given to the experimental techniques that are necessary to achieve broad spectral coverage. Examples are given of the application of the apparatus in the investigation of the torsional isomerization of 2-vinylanthracene and the transient solvation of electronically excited coumarin 440 in alcoholic solutions.

Optical limiting properties of nonlinear multimode waveguides

An experimental investigation of the transmission of multimode capillary waveguides with a nonlinear absorber in the core shows an enhanced nonlinear absorption relative to the same length of bulk material. The results are consistent with partial mode filling within the cores of the waveguides. This study confirms the promising optical limiting capabilities of multimode nonlinear waveguides and implies that the mode structure should be considered in the design and evaluation of capillary array optical limiters.

Double well isomerization in solution: A new comparison of theory and experiment

The first‐excited‐singlet state of each of the compounds 2‐vinylanthracene (2VA) and 2‐(2’‐propenyl) anthracene (22PA) undergoes an electronically adiabatic torsional double‐well isomerization which interconverts a s‐cis conformation and a s‐trans conformation. The forward rate constant kf for the isomerization was measured by picosecond fluorescence spectroscopy as a function of temperature and solvent viscosity η in the range 0.23–3.25 cP, i.e., in the C5–C16 normal alkanes. For 2VA, kf is independent of η within experimental uncertainty (∼5%), while for 22PA kf≂cη−0.23. An effective torsional isomerization potential of the form V(φ)=(V1/2)(1−cos φ)+(V2/2)(1−cos 2φ) was determined from thermochemical data on the isomerization. Torsional well (ω0) and barrier (ωb) frequencies were calculated from the effective potential and the appropriate moments of inertia. With an estimate in hand for ωb, it was possible to directly evaluate theoretical predications from the (i) theory of Kramers and alternatively fro...

Degenerate four-wave mixing experiments on polyacene quinones

Abstract Three representative polyacene quinones doped in thin polymer films have been studied by degenerate four-wave mixing to elucidate the dominant factors in the third-order nonlinear optical effects of these compounds. The experiments have been made near or on resonance at 532 nm. The nonlinear effects of these materials are found to be of electronic origin with rapid response times. The third-order nonlinear optical coefficients are not simply correlated with the delocalization length of the compounds as expected from simple theory.