Novel Organic Sol-Gel Materials for Second-Order Nonlinear Optics
- PDF / 301,418 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 105 Downloads / 215 Views
applications such as frequency doubling and electro-optic (EO) modulation [1,2]. In order to prevent the randomization of the poled (aligned) NLO molecules, NLO chromophores are usually incorporated in a polymer which has a high glass transition temperature (Tg). This is due to the fact that molecular motions of NLO chromophores are closely associated with the Tg of the polymer [3]. Furthermore, enhanced temporal stability of second-order NLO properties in a poled polymer can be obtained when a certain degree of crosslinking is introduced [4-13]. Long term stability of second-order nonlinearities in many different crosslinked polymeric systems at temperatures higher than 100 'C has been reported earlier [6,10-13]. Polymeric materials to be used in EO modulators should possess high EO coefficients and low optical losses at their operating wavelengths [2]. In the case of frequency doubling, design considerations should seek to minimize the absorption loss at the doubled frequency. Even small absorption can cause damage to the material [14]. Therefore, low optical loss of the polymer is a critical factor in both frequency doubling and EO modulation applications. Melamine-based materials have been widely used in the lighting, coating, and decorating industries because of their good transparency [15]. Moreover, the formation of melamine 583 Mat. Res. Soc. Symp. Proc. Vol. 328. ©1994 Materials Research Society
materials involves sequential hydrolysis and condensation. This sol-gel process provides an attractive route to the preparation of a densely crosslinked network. In addition, the high Tg (> 150 'C) of crosslinked melamine-based materials [16] would be expected to stabilize the aligned NLO chromophores by decreasing their mobility. Therefore, melamine-based second-order materials can lead to low optical loss, a dense three-dimensional network, and a high Tg. In the present study, the first preparation of second-order NLO all-organic sol-gel materials was achieved. Two NLO dyes with different absorption characteristics were added to melamine-based prepolymers. After thermal curing and poling, transparent crosslinked melamine films containing NLO moieties were obtained. The linear and nonlinear optical properties of the poled/cured samples were determined. EXPERIMENTAL Hexa(methoxymethyl)melamine (HMM, Resimene® 747, Figure 1) was obtained from Monsanto and was used as received. Prepolymer of HMM (Tg = 2 'C) was prepared by heating the monomer at 220 'C for 1 h in the presence of an acid catalyst. Disperse Orange 3, 4-(4'-nitrophenylazo)aniline (D03, Figure 2a), is available from Aldrich and was used as received. The other NLO dye, 4-amino-4'-nitrobiphenyl (ANB; Figure 2b), was synthesized according to Sherwood et al. [17]. Melamine-based samples doped with either D03 or ANB were studied (HMM/D03 or HMM/ANB). To prepare a prepolymer solution for spin-coating, an NLO dye and HMM prepolymer with a weight ratio of 1:5 were dissolved in propylene glycol methyl ether acetate (PGMEA) with a certain amount of water and aci
Data Loading...
