Z-scan studies of Barium Bismuth Borate glasses

Tree-like dendritic structures based on identical repeat units and a variety of branching patterns are an exciting new class of materials with a myriad of potential applications at the nanophotonics level. Dendrimers offer advantages over traditional linear polymers containing a mixture of chain lengths in that they are monodisperse macromolecules amenable to detailed structure property relationship studies. For the study of multi-photon absorption (MPA), dendrimers can be designed using chromophore repeat units with known photonic properties, and the resulting highly branched three-dimensional structures allow a very high packing density per unit volume, with the number of chromophore repeat units increasing exponentially with dendrimer generation.

New Organic Dendrimers with Greatly Enhanced Multi-Photon Absorption for Photonics Applications

Over the past five years there has been a renaissance in design studies of chromophores with the possibility of enhanced two-photon absorption (TPA) While two-photon absorption has been described for molecules such as laser dyes in solution for a number of years1, it has only been recently that researchers have attempted detailed structure-property relationships to elucidate how new chromophores with greatly enhanced two-photon cross-sections might be designed Since the intrinsic cross-sections are related to the Im component of the third order optical nonlinearity, it should come as no surprise that much of the previous work in the literature which focused on structure-property relationships for molecules with enhanced NLO response might be applicable to the design of new TPA chromophores In this presentation we will review our recent studies in this area, and our rationale for the applicability of dendritic strctures based on photonic-active repeat units for enhancment of two-photon absorption, particularly in the area of optical power limiting applications

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1946427400204387

Optical Power Limiters for Nanosecond Pulses: Design of New Dendritic Chromophores with Exceptionally Large Two-Photon Cross-Sections

Substituent effects are quite important in fine tuning the photonic properties of conjugated molecules. In designing new chromophores, electron-donating or withdrawing substituents affect the electron distribution in the conjugation sequence, and previous studies to establish structure- property relationships have noted that when second row elements replace first row elements in the structure (e.g. S for O in donor groups), large enhancements of both the second and third order optical nonlinearity are observed. However, along with the observed enhancement of the nonlinearity, a red-shift in the absorption spectra occurs, often with peak broadening and tailing. This absorptivity-nonlinearity trade-off has been a constant concern in proposing organic materials for electro-optic device applications. In this presentation we will review our recent activity in designing new chromophores wherein P replaces N in donor groups and dendrimer building blocks, and the consequences and opportunities resulting from the observed large blue shifts in the spectra.

Photonic Properties of Dendrons and Dendrimers Incorporating Bis-(Diphenylphosphino)Diphenylpolyenes

Organic materials with large two-photon absorption are desired for numerous photonics applications, such as optical limiting,upconversion lasing, three-dimensional data storage,and photodynamic therapy. Stilbazolium derivatives are interesting two-photon absorbers for these applications. In this work,the nonlinear transmissivities of trans -4-[4-(dimethylamino)styryl ]-1-methylpyridinium iodide (DASPI), trans -4-(4-aminostyryl)-1-methylpyridinium iodide (ASPI), trans -4-[2-(1-methylpyrryl)vinyl ]-1-methylpyridinium iodide (MPVPI), trans -4-(2-pyrrylvinyl)-1-methylpyridinium iodide (PVPI),and trans -4-styryl-1-methylpyridinium iodide (SPI)at 800,850,900,950 and 1000 nm have been studied respectively using 21 ps laser pulses. The two-photon induced fluorescence of these compounds at 872,900,and 940 nm has also been investigated.All of these compounds exhibit two-photon absorption and two-photon induced up-converted fluorescence in the near-IR wavelengths,and the two-photon absorption cross section and
two-photon induced fluorescence intensity vary with the wavelength and with the chemical structure changes. These preliminary results suggest that it is possible to increase the two-photon absorption cross-sections by proper structure modifications

Wavelength dispersion of two-photon absorption and two-photon-induced fluorescence of stilbazolium derivatives

Model dendrimers based on bis-(diphenylamino)stilbene repeat units have been synthesized and shown to have very stable bipolaronic charge states. Calculations at the AM-1 level predict two orders magnitude enhancement in the third-order nonlinearity in going from the neutral to bipolaron state. Measurement of two-photon cross-sections for PPV dimers with attached diphenylamino donor groups show enhanced two-photon cross-sections for ns pulses. Preliminary evaluation of one of the model dendrimers indicates even larger two-photon cross-sections are possible.

D. Kumar

Papers

Optical Power Limiters for Nanosecond Pulses: Design of New Dendritic Chromophores with Exceptionally Large Two-Photon Cross-Sections

Design and synthesis of dendrimers with enhanced two-photon absorption