Silicon-Bridged donor-acceptor compounds: synthesis and nonlinear optical properties

This thesis describes the synthesis and the spectroscopic and nonlinear optical characterization of a large series of donor- and acceptor-substituted diphenylsilanes with the structure DPh-(SiMez).-PhA and fragments thereof. Nonlinear optics (NLO) deals with the interaction of electromagnetic fields (light) with matter so as to generate new electromagnetic fields altered from the incident field with respect to phase, frequency, amplitude or other propagation characteristics. One of the applications involving nonlinear optical phenomena is frequency doubling of near infrared laser light (frequency a) by a nonlinear optical material into blue light. ... Zie: Summery

Photorefractive polymers with low intrinsic trap density

Two novel photorefractive polymers are presented, based on the charge transport molecule N,N'-diphenyl-N,N'-bis(3-methylphenyl)-[1,1'-biphenyl]-4,4'-diamine (TPD). In one polymer the TPD unit is chemically modified so that it can function both as charge transport and as electro-optic molecule. In the other polymer the TPD is incorporated into the polymeric backbone and provides the charge transport and functions as a host for the dispersed electro-optic molecules. In both types of polymers the trap density is very low, which causing a 90 degrees phase shift between the refractive index grating and the illumination pattern and a rather small photorefractive performance. The trap density can in the case of the bifunctional molecule based polymer be increased by adding small amounts of N,N,N',N'-tetramethyl-paraphenylene diamine (TMPD) which has a lower ionization energy than the bifunctional molecule. This results in a strong increase of photorefractive performance and simultaneously in a lowering of the phase-shift. The ionization energy of some molecules used in photorefractive polymers is determined using gas-phase ultraviolet photoelectron spectroscopy and cyclovoltammetry. Using these ionization energies the process of the space-charge field formation can be understood on the basis of the components of the photorefractive polymer.</p

Transient behavior of photorefractive gratings in a polymer

The transient behavior of photorefractive gratings in the polymer composite poly(N-vinyl carbazole) (PVK), 2,4,7-trinitro-9-fluorenone (TNF), and N,N-diethyl-para-nitroaniline (EPNA) doped with various amounts of 4-(diethylamino)benzaldehyde diphenylhydrazone (DEH) is presented. The influence on the hole drift mobility due to the change in the trap density induced by DEH, was directly measured.

Photorefractivity in poly(N-vinylcarbazole)-based polymer composites

The mechanism of photorefractivity in a family of model composites based on PVK is discussed. Novel aspects of photorefractivity that are unique in polymers are described. The effect of plasticization on their photorefractive performance is investigated. © 1996 IOP Publishing Ltd

Engineering of photorefractive polymers

Photorefractive polymers offer advantages such as their considerable flexibility in synthesis, doping, processing, and low cost. Furthermore, compared to their crystalline counterparts, they offer the possibility of improved value in the photorefractive index change figure-of-merit, owing to the small dc dielectric constant and reasonable linear electrooptic coefficient and refractive index. We have investigated both host-guest, e.g., photoconducting polymers like PVK:TNF doped with electrooptic molecules or electrooptic polyurethanes doped with charge transporting molecules like DEH and sensitizers like TNF and C60. We also have investigated single component polymer materials, where all the necessary functional components are covalently bonded on the same polyurethane backbone. Various trade-offs that exist in photorefractive polymers are examined