The molecular structure / nonlinear optical (NLO) property relationship is explored with seven recently synthesized chromophores. Two symmetrical compounds were made using electron withdrawing groups separated by an electron rich core while five asymmetrical molecules were developed using electron donating and withdrawing groups coupled by a it electron bridging group. Pendant chains were added to some of the chromophores to improve processibility. Their syntheses are described and their optical limiting properties discussed.

Strong optical limiting and large two-photon absorptivities are reported for a class of bisdonor diphenylpolyene derivatives with varying polyene bridge lengths. These molecules exhibit strong optical limiting using nanosecond pulses over a broad spectral range. Bis(diphenylamino)stilbene exhibits a 90 nm red shift of its optical limiting band, and only a minimal shift of about 13 nm of its lowest one-photon electronic absorption band relative to bis(di-n-butylamino)stilbene. This suggests a potential for broadband optical limiting with high transparency using mixtures of such compounds. Pulse width dependent nonlinear transmission measurements suggest that two-photon pumped excited-state absorption contributes significantly to the limiting of nanosecond pulses.

We studied the optical nonlinearities of modified 3,3′-diethylthiadicarbocyanine iodides (X-DTDCI) in dimethyl sulfoxide (DMSO) solutions (X = H, Cl, Br at meso position) by a pump-probe technique with crossed polarized chirped laser pulses at room temperature. Reverse-saturable-absorption (RSA) with monoexponential lifetimes is observed at 532 nm in all the samples studied. We determined the effective excited-state absorption cross-sections and their lifetimes for all the samples investigated and found that they clearly correlate to the substituent X at the meso position. Empowered by the chirped pulses, a much faster nonlinearity with a decay time of ˜3.1 ps that is much shorter than the laser pulses used, is unveiled in Cl-DTDCI. We expressed both the absorptive and the refractive part of this fast nonlinearity as the equivalent molecular hyperpolarizability γ1212 and found γ1212 = (8.1 + i9.8) × 10−32erg−1.

Optical limiting, degenerate four-wave mixing and transient absorption experiments have been performed on a neat liquid lead substituted phthalocyanine. The photophysical mechanisms responsible for the good optical limiting observed in other phthalocyanine solutions are maintained in this pure liquid despite its different peripheral substitution pattern. The liquid is shown to have excited state absorption cross sections that exceed those of the ground state through much of the visible spectrum. Hybrid absorptive/refractive nonlinear response is demonstrated to contribute to both the four-wave mixing and optical limiting response. The mechanism and states responsible are discussed.

Measurements of sensitive RSA phenonema in new porphyrin dyes are presented. Both the linear and non-linear optical properties are shown to depend strongly on the molecular structure. A detailed analysis of two of the porphyrins reveals that inter-systems crossing rate and the excited state absorption profile are strongly influenced by substitution of a heavy atom into the central atom position. It is shown that by appropriate choice of wavelength values in excess of 30 can be achieved for the material parameter σex / σgr. This value compares well with previously reported results and is achieved in conjunction with excited state lifetimes on the order of 300 ns.

Nonlinear optical properties of asymmetric pentaazadentate expanded porphyrin metal complexes are investigated. The transmittance dependence of the target compounds on the incident laser intensity generates different nonlinear optical effects in the excited states. The reverse saturable absorption at 532 nm in the ns pulses and the saturable absorption for the pspulses at high fluences are observed in solutions. The nonlinear refractive indices n2 aremeasured by the Z-scan technique. The optical limiting based on the RSA and transverse refraction are demonstrated for ns and continuous laser. An optical limiter based on the RSA and self-refraction is performed, in which the limitating threshold and amplitude of output energy are reduced.

We characterize the optical properties of modified meso-alkynyl porphyrins by a number of techniques. Our data show that extending the conjugation and incorporating metal in the center of the ring in these molecules serve the objective of tuning the absorption maximum wavelength. We evaluate the optical limiting performance by determining the effective reversesaturable- absorption (RSA) lifetime and the change in the absorption cross-sections. The ultimate optical limiting performance of these molecules is tested in both picosecond and nanosecond regimes.

Photoexcitation of a new pure liquid phthalocyanine gives both a strong nonlinear absorption and photoalectrical charge generation. The novel photoelectrical properties of the material lead to plasma formation, an additional limiting mechanism, at moderate fluences.

During the past decade, there has been considerable effort in the design of new materials with greatly enhanced nonlinear absorption characteristics. In recent years, it has been shown that incorporation of bipolaronic charges in the pi-electron sequence in conjugated polymers or copolymers leads to enhanced third-order nonlinear optical properties. In this current study a design strategy for the synthesis of optical power limiting copolymers is presented whose properties are based on the photogeneration of stable bipolaron-like dications.

Fullerene chemistry is booming, but how the chemical reactions affect fullerene's materials properties has seldom been studied. We have investigated optical limiting behavior of a series of fullerene derivatives, polymers, and glasses and have observed the following structure-property relationships for optical limiting in the fullerene materials: (i) The fullerene polymers with aromatic and chlorine moieties, i.e., C60-containing polycarbonate (C60-PC), polystyrene (C60- PS), and poly(vinyl chloride) (C60-PVC), limit the 8-ns pulses of 532-nm laser light more effectively than does the parent C60; (ii) the fullerene polymers with carbonyl groups, i.e., C60- containing CR-39 (C60-CR-39) and poly(methyl methacrylate), (C60-PMMA), do not enhance C60's limiting power; and (iii) the aminated fullerene derivatives, i.e., HxC60 (NHR)x [R = -(CH2CH2O)2H (1), x = 11; -(CH2)6OH (2), x = 7; -cyclo-C6H11 (3), x = 11; -(CH2)3Si(OC2H5)3 (4), x = 4], and their sol-gel glasses, i.e., 1–3/SiO2 (physical blending) and 4-SiO2 (chemical bonding), show complex limiting responses, with 4(-SiO2) performing consistently better than 1-3(/SiO2). The fullerene glasses are optically stable and their optical limiting properties remainunchanged after being subjected to continuous attack by the strong laser pulses for ca. 1 h.

The fullerene materials are well known for their non-linear behaviour arising from excited state absorption processes. In solution, the processes can set in at low irradiance levels, although evidence is building that the magnitude of the effects is dependent on the solvent used in the experiments and the role of charge transfer processes. In evaporated films of C60, the solvent is absent and reduced non-linearities are seen as irradiances approach the laser damage threshold of the films. When the chromophor is incorporated into polymer films, non-linear processes are found at the same levels as the solution case provided that some residual solvent remains in the composite. Excited state absorption spectra suggest that some ionisation of the C60 may be occuring.

This paper presents the results of the bulk laser damage performance of undoped epoxy thermosets with glassy and rubbery mechanical properties and two commercial polymethylmethacrylate (PMMA) samples. We demonstrate how thermomechanical properties such as glass transition temperature (Tg) and equilibrium shear modulus (Ge) affect laser damage threshold. The rubbery epoxy elastomer shows a damage threshold fluence one order of magnitude higher than PMMA and 2.5 orders of magnitude higher than a glassy epoxy thermoset. A solid-state guest-host limiter is made by doping the epoxy elastomer with zinc octabromotetraphenylporphyrin (ZnOBP). The limiting performance of the elastomer limiter is compared to a solution of ZnOBP and C60 in toluene. Photochemical hysteresis effects in the solid limiter were also investigated.

Phthalocyanines (PC's) containing heavy metal central atoms have recently been recognized as leading candidates for reverse saturable absorption and optical limiting (OL) applications in the visible spectrum. Strong triplet excited state absorption brought about by a large intersystem crossing rate is responsible for the excellent limiting performance of these molecules. Moreover, devices which maximize the excited state population along the light path will demonstrate maximum limiting efficiency. A non-homogeneous distribution of indium tetra(tert-butyl) phthalocyanine chloride (InC1PC) has been shown to be very effective in attenuating 532 nm nanosecond laser pulses. This was accomplished by approximating a hyperbolic distribution of chromophores using discrete elements of fixed dye concentration. Greater OL should be achieved by fabricating materials containing a continuous concentration gradient of chromophore. This paper focuses on issues concerning the preparation of solid polymeric materials that contain such a chromophore gradient. This design is achieved by diffusing chromophore-containing solutions into partially polymerized poly(methyl methacrylate) (PMMA).

Pd and Zn - tetraphenyltetrabenzoporphyrins (PdTPTBP and ZnTPTBP), hexacyanin 3 (HITCI), and substituted phthalocyanines were incorporated in solid-state matrices (xerogels) using a sol-gel process. Nonlinear reverse saturable absorption was observed with those materials when they were illuminated with nanosecond laser pulses at 532 nm, or other wavelengths in the visible spectrum (between 450 nm and 630 nm). PdTPTBP doped xerogels exhibit a nonlinear activation threshold of about 10 mJ/cm , which is much lower than the value of 80 mJ/cm2 obtained under similar conditions with classical Al phthalocyanine chloride, or HITCI molecules. Solid state “red active” reverse saturable absorbers can be obtained with substituted phthalocyanines doped xerogels. The different experimental results are discussed using classical 4- energy level diagrams.

Photoinduced intermolecular charge transfer (PICT) in donor/acceptor systems has been investigated as an approach to the design of new optical limiting (OL) materials. Solution of cyanines or porphyrins (as sensitizers) and viologen derivatives (as electron acceptors) were used in these studies. Picosecond time-resolved fluorescence measurements were carried out to estimate the charge-transfer rate in these donor/acceptor systems. The radical-ion absorption bands were identified using spectroelectrochemistry. Nonlinear transmission measurements with picosecond and nanosecond laser pulses were utilized to determine the effective photo-induced to ground-state absorption cross-section ratio of the sensitizers alone and the sensitizer/acceptor systems. Our studies are consistent with optical limiting by PICT in solution and indicate a substantial radical-ion yield in the systems examined.

Pulsed-laser shadowgraphs and images of scattered light are combined with limiting and scattering data to build a model of the response of silicon napthalocyanine (SiNc) at concentrations on the order of 10−3 M in toluene to 12–16 ns 532 nm laser pulses over an energy range from 10 nJ to 2 mJ. The inherent spherical aberration induced by the sample has a profound effect on the response. The scattering is extremely intense above pulse energies of 100 μJ. The data indicates the response at pulse energies below 300 mJ is due to reverse saturable absorption. Full absorbance is not observed until the agglomerates vaporize. At fluences approaching 1 J/cm2 a plasma begins to form and the liquid near the window starts to boil. Intense scatter from the boiling liquid combined with plasma absorption produces hard clamping.

Brilliant, iridescent colors found on the bodies and wings of many birds, butterflies and moths are produced by structural variations and have been the subject of study for centuries. Such brilliant colors have been described as metallic colors due to the saturation or purity of the color produced and have attracted the attention of great scientists like Newton, Michelson and Lord Rayleigh. It was recognized early on that such colors arise from physical effects such as interference or diffraction as opposed to colors that are normally produced due to the presence of chromophores which absorb or emit light. Common examples of physical colors are some butterfly wings [1], color of Indigo snake skin [2], hummingbird feathers [3,4], arthropod cuticles [which are due to selective reflection of color from the solidified cholesteric phase of chitin crystallites] [5], gemstones like opal [6,7], and some crystals like potassium chlorate [8]. While the origins of such colors are well understood the properties of color and color specification have not received much attention.

Two chitosan gel systems, chitosan/acetic anhydride and chitosan/glutaraldehyde, were studied as host materials for optical limiters. Both gels are transparent and have a very high laser damage threshold. The chitosan/acetic anhydride gel has a damage threshold > 540 J/cm2 while the chitosan/glutaraldehyde gel, which is slightly yellow in color, has a damage threshold > 600 J/cm2 (measurements made with 6.8 ns laser pulses at 532 nm). Different chromophore dopants, including porphyrin and CuPc, were tested. The optical limiting behavior of the guest/host gel systems was similar to their corresponding solution systems. The morphological structure of the gel systems was studied and the gelation process is discussed. Our current research explores the effect of gel morphology on the optical limiting properties of the chromophores and studies the relation between chromophores, cross-linking agents and the host materials. We have also investigated the relationship between optical properties and chemical structure of the gel/chromophore systems in order to optimize the optical behavior.

The photophysics and nonlinear absorption behaviour of a series of α, ω-dithienyl polyenes were studied in chloroform and n-octane solutions. Steady state fluorescence, fluorescence lifetime and quantum yield measurements were made. The fluorescence quantum yields were significantly lower than those of the corresponding ax,o-diphenyl polyenes. Among the dithienyl polyenes, 3,3′-substituted polyenes exhibited stronger fluorescence than those of the 2,2′-substituted. Nonlinear optical absorption experiments showed evidence of two photon absorption.

Crystalline thin films of NdNiO3 are known to exhibit characteristic metal-insulator electrical transitions. Infrared transmission measurements of these films have demonstrated the corresponding reversible optical switching response, transforming between IR-transparent and IR-opaque states. Their low-temperature transmission spectra exhibit a sharp increase in transmittance at an onset wavelength of approximately 3 mm (˜0.4eV), with an appearance suggesting formation of a distinct band gap structure. The transmission and reflection characteristics of these films differ significantly from those reported for bulk polycrystalline material.