Sheik A. Zahir

Optical waveguiding and nonlinear optics in high quality 2‐docosylamino‐5‐nitropyridine Langmuir–Blodgett films

The linear and nonlinear optical properties of well‐ordered Y‐type Langmuir–Blodgett (LB) multilayers of 2‐docosylamino‐5‐nitropyridine (DCANP) have been investigated. The nonlinear optical susceptibilities have been determined for the wavelengths λ=1064 nm [d33=(7.8±1) pm/V, d31=(2.0±0.5) pm/V] and λ=1318 nm [d33=(5.6±1) pm/V]. In first waveguiding experiments carried out TE0 and TM0 modes propagating over more than 20 mm could be excited. Coupling experiments allowed the determination of the dispersion of the refractive index n3 (n632.8 nm3 =1.598). Guided wave attenuation coefficients as low as 12 dB/cm (at the wavelength λ=632.8 nm) are reported.

Investigation of chromophore orientation of 2-docosylamino-5-nitropyridine and derivatives by nonlinear optical techniques

Abstract 2-Docosylamino-5-nitropyridine (DCANP) is a strongly nonlinear optical molecule which forms high optical quality Langmuir-Blodgett (LB) films. DCANP shows higher nonlinearities as compared to its aliphatic chain derivatives (C18H37 to C26H53). To explain this we determined the orientation of the chromophores and the hyperpolarizabilities by means of nonlinear optical techniques.

Polymerized non-linear optical Langmuir-Blodgett films based on 2-(21-docosenyl)amino-5-nitropyridine

Abstract Using the Langmuir-Blodgett (LB) technique, multilayer films of 2-(21-docosenyl)amino-5-nitropyridine have been made by transferring stable monomolecular films from an air-water interface onto quartz substrates. Such multilayer films can be polymerized by X-ray irradiation. The films exhibit the same enhanced second harmonic generation efficiency before and after polymerization. No change in the morphology of the films has been observed after polymerization, probably because the vinyl group is at the terminal position of the hydrocarbon chain.

Optical second-harmonic generation from polymerized Langmuir-Blodgett films of 2-(21′-docosenyl)amino-5-nitropyridine

Abstract Thin films of 2-(21′-docosenyl)amino-5-nitropyridine (VECANP) have been prepared by the Langmuir-Blodgett (LB) method. Subsequently the films were polymerized by X-ray irradiation. UV/VIS-spectroscopy showed that the light transparency range extends from 450 nm to at least 2000 nm. The dispersion of the nonlinear optical susceptibilities d 33 and d 31 have been determined in the wavelength range between 840 nm and 1318 nm. The different solubilities of polymerized and non-polymerized VECANP in n-hexane offers the possibility to structure the films laterally (for example to fabricate strip waveguides); a necessary condition for application in integrated optics.

IR analysis of Langmuir-Blodgett films for nonlinear optics

Abstract From polarized IR spectra of DCANP and four N-alkyl homologues, the dichroic ratios of the NH, the antisymmetric (va) and symmetric (va) CH2 vibrational absorptions are calculated and compared to reported results from polarized UV spectra. The orientation of the NH group in most pronounced for the n = 26 homologue. Similarly the CH2 chains tend to be more regularly oriented with increasing length. The increasing order of the chromophores explains the increase in the second order susceptibilities for the homologues with n = 18, 20 and 22 carbon atoms in the chain.

Waveguiding and nonlinear optics in 2-docosylamino-5-nitropyridine Langmuir-Blodgett films

Read-out of volume phase holograms in photorefractive crystals with a wavelength that is different from the wavelength of hologram formation imposes the difficulty to match the Bragg condition for all spatial frequencies of the object to be stored. Therefore, the quality of the reconstructed image decreases and resolution and image field losses are observed. Experimental and theoretical examinations of these effects reveal that the geometrical configuration of the writing experiment determines the reconstructed image field. Depending on the wavelength of read-out an appropriate reconstructing wave can be formed with the help of lenses diminishing image field and resolution losses considerably.