Braja K. Mandal

Cross‐linked stable second‐order nonlinear optical polymer by photochemical reaction

A new method for obtaining cross‐linked second‐order nonlinear optical polymer by photochemical reaction has been described. An active dye was processed and poled in a photoreactive polymer in a manner similar to doped polymer system, and photo‐cross‐linked in the poled phase by ultraviolet irradiation. The dye doped (20% by weight) cross‐linked polymer has a nonlinear optical coefficient d33 of 5.1 pm/V at 1.540 μm and shows no relaxation after being subjected to thermal treatment at 60 °C for 0.5 h.

Photocrosslinkable Polymers with Stable Second Order Optical Nonlinearity

Abstract Linear and nonlinear optical properties of photocrosslinkable polymers are reported. These polymers exhibit relatively stable second order nonlinearity. Electro-optic and second harmonic generation coefficients are reported for these new materials.

Thin film processing of NLO materials—I. Studies on relaxation behaviour of corona poled aromatic dipolar molecules in a polymer matrix

Abstract A number of corona poled guest-host systems have been investigated to elucidate the nature of interaction between the guest and the host molecules, their compatibility and relaxation behaviour. This study has been carried out by examining the relaxation response of the nonlinear optical effects. Styrene/acrylonitrile copolymer was found to be the ideal matrix studied, since the polymer itself relaxes slowly subsequent to poling and it accommodates a wide range of nonlinear optical molecules differing in molecular structure and polarity. Retention of the second-harmonic intensity has been emphasized as a measure of the relaxation and decay of the order parameters with time. Absorption characteristics of the poled and the unpoled film are also described.

Thin film processing of NLO materials. VII a new approach to design of cross-linked second-order nonlinear optical polymers

Abstract A new class of cross-linked second-order nonlinear optical (NLO) polymers has been developed by processing a NLO-dye and a polymer similar to conventional ‘doped polymer’ system. Intermolecular cross-linking was carried out by UV radiation subsequent to electric field induced poling of the composite. Cinnamate (C 6 H 5 − CH = CH − CO 2 − ) and styrylacrylate (C 6 H 5 − CH = CH − CH = CH − CO 2 − moieties are selected as the photoreactive chromophores which are attached to both the NLO molecules at two positions and randomly substituted to a vinyl polymer. The poled cross-linked polymers exhibit stable nonlinear activity over a long period of time as characterized by temporal response of second-harmonic generation signal and UV absorption characteristics.

Photocross-Linked Second Order Nonlinear Optical Polymers

We report a novel method to obtain stable second order nonlinear optical (NLO) properties in polymeric thin films. Photocross-linking between the NLO active molecules and a photoreactive polymer is achieved by UV irradiation subsequent to poling. The thin film exhibits a nonlinear coefficient d 33 of 16.5 pm/V at a doping level of 20% by weight of NLO active molecules and possesses quite stable second order nonlinear optical properties

Linear and Nonlinear Optical Properties of a Comb-Like Polymer

Linear and nonlinear optical properties of a comb-like polymer, viz. copolymer of methylmethacrylate (MMA) and 4-[4-(-methylacryloxy) octyloxy 2-methylphenyliminomethyl] cyanobenzene, are described. The second order nonlinear optical coefficient and the short and long term decay constants of second harmonic generation (SHG) intensity of the poled polymeric films are obtained from SHG measurements. The stability of the second order nonlinear optical properties is monitored by studying the time behavior of SHG. The Waveguiding loss was found to be 1 dB/cm.

Optimized Processing Condition for a Photocrosslinkable Stable Nonlinear Optical Polymer

The optimum processing condition for a photocrosslinking Nonlinear Optical(NLO) polymeric system was established. Parameters such as change in heat capacity at glass transition temperature, rate of decrease of absorbance of residual uncrosslinked chromophores, and measurement of mass loss upon heating were used to set up the optimum condition. Poly(vinyl cinnamate) was used as the photocrosslinkable polymer and 3- cinnamoyloxy-4-[4-(N, N-diethylamino)-2-cinnamoyloxy phenyl azo] nitrobenzene was used as the NLO molecule. Poling at 70°C for 5 minutes followed by photocrosslinking with a dose of 2.5 mW/cm 2 for 10 minutes results in a stable second order nonlinear optical material.

Nonlinear Optical Properties of New Dye Doped Photocrosslinkable Polymers

Polymeric materials are playing an increasingly important role in electronic and photonic applications 1–4 This includes application in active devices utilizing optical effects attributable to the nonlinear polarization of the medium. A number of applications such as frequency mixing, second harmonic generation, optical bistability, optical parametric amplification and oscillation, electrooptic and all optical switching and modulation etc. have been proposed.

Optical and Electro-Optical Properties of a Photocross-Linkable Polymer

Abstract : Planar waveguides from a photocross-linkable polymer have been fabricated on glass and SiO2 on silicon using the spin coating process. The polymer has been cross-linked by exposure to UV radiation (lambda = 254 nm). Prism coupling technique has been used to couple a laser beam into the waveguide structure. The waveguiding parameters such as number of modes, loss, thickness and index of refraction of the polymer have been determined before and after cross-linking. The refractive index of the polymer before cross-linking differs significantly from that after cross-linking. No anisotropy has been observed in the refractive indices for the uncross-linked or cross-linked samples. The refractive index and thickness of the polymer film before and after cross- linking have also been measured using an ellipsometer and found to be in very good agreement with those obtained by the prism coupling technique. Dye molecules with large second order hyperpolarizability were utilized as guests into the photocross-linkable polymer matrix for second order nonlinear optical applications. Electro-optic properties of this polymeric system are reported.