Extensive measurements and modeling of several two photon absorbing materials are described. These are used to elucidate the relative significance of various relaxation and excitation processes that come into play in nonlinear transmission (NLT) and two photon absorption cross section measurements. A reliable measurement of the one photon absorption cross sections at energies 0.5 to ~1.7 eV below the fundamental transition are presented with Voigt function fits that enable the determination of the Gaussian and Lorentzian line widths. Both a numerical model and an analytical model are developed neither of which use any adjustable parameters in comparing calculated NLT results to data. Both models fit the data relatively well over the full range of the experiment. The analytical model captures the primary causes of the nonlinear absorption in the low intensity regime and demonstrates that the nonlinear transmittance can be estimated as a simple effective three-photon process. The numerical model calculates the spatial and time dependence of three state populations and all of the transitions between these states. This model improves the quality of the nonlinear transmission fit which is due to the inclusion of the ground state absorption. Additionally an observation of a strong, long lived transient which is quenched by oxygen suggests multiphoton ionization is happening at low intensities. Thus the full range of constraints applicable to all measurements of the two photon cross section are presented.

We have fabricated a polymer solid-state microcavity in the laser gain media by two-photon-induced polymerization technique. The photopolymerization resin contains conventional laser-dye and dendrimer. A dendrimer can encapsulate the laser-dyes, limiting cluster formation and intermolecular energy transfer, and promising a high level of optical gain. The effect can be extended to prepare an optically active microstructure using the two-photon-induced polymerization technique. We fabricated a polymeric microcavity, which consisted of <400 nm-linewidth strips arranged in layer-by-layer structure. The periodic variation in the refractive index gave rise to Bragg reflection. A laser emission was measured in the microcavity under optical excitation. The spectral linewidth was about 0.1 nm above the lasing threshold. The laser emission is attributed both to the distributed Bragg reflection and to the high gain of a polymer medium containing laser-dye with a high concentration.

Alkynyl platinum derivatives and thiacalixarenes were trapped in solid transparent matrices prepared by the sol-gel process. By using functionalyzed silicon alkoxides, molecular species were grafted to the gel matrix giving a high doping concentration and chemically stable materials. In this communication we present broadband optical limiting performance in the visible wavelength region observed in the prepared materials.

Differential optical Kerr effect (DOKE) detection is a powerful tool for studying the ultrafast time-resolved dynamics of 3^rd-order nonlinear processes. In this study, DOKE was used to measure the nonlinear absorption properties of tetraethynylphenylene (TEP) solutions in THF using 800 nm, 80 fs laser pulses. These two-dimensional, highly-conjugated chromophores (also known as TPEBs) show high instantaneous two-photon absorption (TPA) for relatively small chromophores. The TPA cross section is strongly dependent on the donor-acceptor geometry in these materials: a quadrupolar, all-donor TEP shows the smallest TPA, with a cross-section of σ⁽²⁾= 90 ± 15 GM. ortho-TEP, for which the donors (and acceptors) are conjugated via the ortho position across the central phenyl ring, is dipolar and displays the largest cross-section, of σ⁽²⁾= 260 ± 30 GM. para-TEP, which is quadrupolar, and meta-TEP, which is dipolar, display similar cross-sections of σ⁽²⁾= 160 ± 10 GM and σ⁽²⁾= 150 ± 10 GM, respectively. In addition to an instantaneous TPA response, these isomers show unique two-photon assisted excited-state absorption (ESA), with the ortho- and meta-TEP displaying a clear 3-10 ps rise to an ESA peak, and subsequent decay. The differences in the nonlinear absorption behaviour of these materials may be partially explained by selection rules and UV-vis spectroscopy. In addition, the polar geometries, coupled to the various in-plane conjugation paths, may further influence their optical nonlinearities. Understanding these trends impacts both the design of materials with desirable nonlinear absorption properties and our understanding of the electronic landscape in functionalized organic materials.

Purified deoxyribonucleic acid (DNA), derived from salmon milt and roe sacs, waste products of the Japanese fishing industry in Hokkaido, has been processed into a promising, optical waveguide quality, biopolymer material suitable for both passive and active optical and electro-optic applications. Intercalation of aromatic compounds into stacked layers within the double helix of DNA molecules has rendered active optical waveguide materials with excellent nonlinear optical properties.

Deoxyribonucleic acid (DNA) extracted and purified from salmon roe and milt sacs, a waste product of the fishing industry was studied for molecular binding and photoluminescence effects using bromocresol purple (BCP). Since BCP is both water and alcohol soluble it was investigated for binding efficiency in DNA/water solutions and modified DNA-CTMA/butanol solutions. Circular dichroism studies show that there is a maximum binding concentration of BCP in the DNA/water solution at ~5% by weight of BCP:DNA. In contrast, DNA-CTMA/butanol solutions showed increased binding concentrations up through 10wt% BCP:DNA-CTMA. This apparent binding affinity of DNA-CTMA for BCP also resulted in a significantly higher (6x) photoluminescence in thin film form when compared to BCP:PMMA films of the same doping concentration.

Deoxyribonucleic acid (DNA), extracted from salmon sperm through an enzyme isolation process, is precipitated with a surfactant complex, cetyltrimethl-ammonium chloride (CTMA), for application as a nonlinear optical (NLO) material. Preliminary characterization studies suggest DNA-CTMA may be suitable for use as the host material in the poled core layer of electro-optically-active waveguide devices. Further studies have also indicated that it may be possible to create an all-DNA-CTMA NLO waveguide device using DNA-CTMA as both the core and cladding materials. Challenges and accomplishments in creating an all-DNA-CTMA waveguide device are discussed as well as poling results and techniques for poled-chromophore-DNA-CTMA films. Optical characterization studies, including optical propagation losses, of the DNA-CTMA films are presented.

Recent years have seen considerable interest in the possibility of using rare earth chelates as emissive materials in organic media. Lanthanides luminescence is quite interesting in applications requiring high spectral purity (for example in OLEDs), or infra red luminescence, in active optical waveguides for telecommunications. The use of organic optical amplification modules is attractive for their ease of fabrication, and therefore their potential low cost, but the high losses at NIR wavelength and the limitation of the emission lifetime due to the quenching effect of the organic matrix greatly limits their performances. However, rare earth chelates offer the possibility to reduce by several orders of magnitude the pump power needed for population inversion, using the absorption of the organic ligand followed by an energy transfer to the rare earth ion. By choosing a ligand with a high molecular absorption, it should then be possible to balance the short emission lifetime and hence to obtain optical amplification. We report on the synthesis and characterisation of the optical near infrared properties of an erbium phthalocyanine. The complex shows very high absorption in the 670nm region, is highly soluble and shows minimum concentration quenching effect. The red absorption could allow the use of standard laser diode as pump source in a planar polymer amplifier device.

We present the results of a study of the optical properties of an organic dye, (1,4-Bis[2-[4-[N,N-di(p-tolyl)amino]phenyl]vinyl]benzene)-doped polymer for photonic device applications. We have measured considerable modal gains of up to 33 cm^-1 at 501 nm at a range of pump fluences using the variable stripe length method. In addition, we have incorporated the material into a planar waveguide laser, which operates at a low-lasing threshold. The measured laser threshold agrees well with that predicted for a 1-cm Fabry-Perot type cavity. We have also made 80-micron diameter microrings, which operate at a low lasing threshold and exhibit lasing in a small number of narrow, well-defined cavity modes.

Fluorene-based molecules were studied in detail as candidates for two-photon absorption (2PA) applications. Previous studies were carried out over the wavelengths range 560 - 900 nm. In this work we have extended our studies to shorter wavelengths in order to determine behavior closer to the 2PA resonance peak. We used picosecond pulses at 532 nm for performing open and closed aperture Z-scan measurements, in order to obtain both the real part of the third order nonlinearity (χr⁽³⁾), corresponding to nonlinear refraction (n₂) and the imaginary part of the third order nonlinearity (χi⁽³⁾), corresponding to nonlinear absorption (β) due to 2PA. We studied several fluorene-based molecules, which differ by length of conjugation system and substitution moieties. From open aperture Z-scan measurements we obtained the imaginary part of the third order nonlinearity (χi⁽³⁾). We measured 2PA cross-sections, δ, varying from 1,000 up to 10,000 GM at 532 nm. The influence of the molecular structure on δ was examined. For some of the dyes we also measured n₂ via closed aperture Z-scan measurements. By subtracting the contribution of the solvent from the observed value for the solution, we obtain the contribution to n₂ due to the solute.

The design of the Large Laser Facility incorporates a type-I-type-II third harmonic generator to convert the 1.053μm fundamental wavelength of the laser amplifier to a wavelength of 0.351μm for target irradiation. To understand the design of frequency conversion system, we have carried out a series of theory researches and experiments, including parameters optimization of the third harmonic converter, experiments on high-intensity third harmonic generation (THG), researches on Transverse Stimulated Raman Scattering (TSRS) in the converting crystal and on broad-band third harmonic generation.

Molecular two-photon absorption (TPA) has attracted a lot of interest over recent years due to the many applications it offers both in biological imaging and in material science, constantly needing new optimized molecules with large TPA cross-sections. Various structures and functional groups have been studied; however, the use of electron-withdrawing boron groups has not been fully examined yet. As such compounds are known to lead to interesting photoluminescence and nonlinear optical (NLO) properties, we have investigated the TPA properties of a novel series of A-π-A quadrupoles, based on dimesitylborons as acceptor end-groups. Our experimental study reveals that intramolecular charge transfer is a crucial point in these TPA fluorophores, and can be modulated via changing the planarity of the molecule. We have obtained such planar molecules using vinylene spacers, which can release the steric hindrance close to the dimesitylboron end-group. The series of NLO-phores described here is promising for optical power limiting, with excellent TPA/transparency trade-off, and the work has highlighted that perfluorophenylene could be a key component for the future of TPA.

In this paper we measure three-photon absorption spectra and cross sections of two new series of molecules, linear bis-difluorenylamine-substituted oligofluorenylene-vinylenes (N-Fl₃ series) and triphenylamine-branched phenylacetylene dendrimers (N-PA₃ series). Using our model described before, we evaluate the size of coherent domains in these two series and compare them to those in dendrimers with nitrogen branching center and stilbene branches. This allows us to draw the conclusions about the effect of dimensionality (linear oligomers versus dendrimers), topology of the dendrimer core (3-arm versus 4-arm core), and branch structure on the size of coherent domains, and, hence the strength of cooperative enhancement of multiphoton absorption in macromolecules.

We demonstrate high contrast interference fringes when near-IR frequencies and UV frequency 3ω excite fluorescence via two alternative but in practice indistinguishable quantum pathways. We use specially synthesized organic dendrimers with an exceptionally large three-photon cross section, σ₃=1.5 10^-79 cm⁶ s² based on bisdiphenylamino stilbene core and bis-diphenylamino di-styryl benzene repeat units. We show for the first time that quantum interference signal can be strong enough for being observed with an unaided eye.

Some aspects of manifesting the nonlinear optical transmission in erbium doped single-mode fibers are considered from the viewpoint of creating all-optical fiber amplifiers. Then, we study analytically originating the steady states for bright ultrashort optical pulses. This type of optical solitons can be grown due to resculpturing external optical pulses by erbium doped fiber in the traveling-wave regime. The model related to the most desirable practically fundamental solitons is taken and, in so doing, we examine the regimes without gain saturation in doped fibers and demonstrate that these fibers can support well localized optical pulses representing the bright dissipative optical solitons.

The photo-physical properties of bis((4-(phenylethynyl)phenyl)ethynyl)bis(tributylphosphine) platinum(II) with 2,2-bis(methylol)propionic acid (bis-MPA) dendritic substituents were studied. The introduction of dendrimer capping was found to give rise to protection from oxygen quenching of phosphorescent states with a considerably longer decay time of the phosphorescence (0.1 -0.4 ms range) for solvents with oxygen removed or dendrimers of larger size (G2-G4) or higher concentration. Presence of oxygen reduces the phosphorescence decay time to below 1 microsecond. Two-photon induced fluorescence and z-scan of fs pulses at low pulse repetition frequency at approximately 720 nm revealed that the two-photon absorption cross-section is in the order of 0.01 cm/GW, well below the 0.34cm/GW reported by Staromlynska et al [J. Staromlynska, T. McKay and P. Wilson, J. Appl. Phys. 88, 1726 (2000)] and similar for all dendrimer complexes as well as the non-capped Pt-acetylide. Z-scans performed at high pulse repetition frequency gives an apparent two-photon absorption cross-section that is higher due to the population of excited triplet states, and the contribution from incoherent multiphoton absorption involving the triplet states.