M. Flörsheimer

Cerenkov-type phase-matched second-harmonic generation in DCANP Langmuir-Blodgett film waveguides

Abstract We report for the first time guided-wave second-harmonic generation in nonlinear optically active Langmuir-Blodgett (LB) films. Phase-matched frequency-doubling was observed in LB films of 2-docosylamino-5-nitropyridine (DCANP) by using the Cerenkov-type configuration. The charge transfer axis of the DCANP molecules essentially lies in a plane parallel to the dipping direction. Therefore the largest nonlinear optical coefficient d 33 could be used by exciting TE modes propagating in the film. Gratings were used to couple light at λ= 1064 nm into the LB film waveguide.

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.

Surface‐emitted green light generated in Langmuir–Blodgett film waveguides

We demonstrate second‐harmonic generation due to counterpropagating beams in planar waveguides of 2‐docosylamino‐5‐nitropyridine (DCANP). The DCANP molecules were deposited by Langmuir–Blodgett techniques and have a preferred alignment within the substrate plane. Four‐layer waveguide structures were used to optimize the trade‐off between propagation loss and efficient surface‐emitted green light.

Submolecular details of Cd arachidate Langmuir-Blodgett films detected by atomic force microscopy

Abstract Submolecular details of the hydrophobic surface of Langmuir-Blodgett films are detected by atomic force microscopy for the first time. The uppermost hydrogen atom is distinguished from the two other hydrogen atoms of the methyl groups.

Lattice constants and range of order of Cd arachidate Langmuir-Blodgett films determined by atomic force microscopy☆

Abstract Long range orientational and short range translational order is revealed by atomic force microscopy for the lattice of the hydrocarbon chains of Cd arachidate Langmuir-Blodgett films. This result is qualitatively in agreement with results previously obtained from integral measuring techniques. The local probe technique, however, also reveals the origin of this order: the short translational correlation length is due to local variations of the molecular density. It is not due to high densities of dislocations. The films do not represent hexatic phases which have been described in theories of two-dimensional melting processes. Tip/sample influences are also investigated in order to make sure that the mechanical scanning process does not disturb the specimen in an uncontrolled way. A systematic enlargement of the lattice is detected and explained with a simple model. A method to determine correct lattice constants from soft organic samples by atomic force microscopy is described. Previous studies where such artefacts have not been reported are discussed.

Lattice constants of Langmuir-Blodgett films measured by atomic force microscopy

Langmuir-Blodgett (LB) films are examples of soft organic and related biological samples. Therefore it is essential to make sure that the mechanical scanning process does not disturb the specimen. We describe atomic force microscopy measurements of the lattice constants of Cd arachidate LB films. A lattice constant dhk is revealed correctly by scanning parallel to the corresponding lattice line [hk]. Scanning in deviating directions enlarges the lattice spacing. The phenomena are explained with a simple model. Previous studies where such artefacts have not been reported are discussed.

Guided-wave frequency-doubling in Langmuir-Blodgett film waveguides

We demonstrate phase-matched frequency-doubling in Langmuir-Blodgett film waveguides of 2-docosylamino-5-nitropyridine. Using the Cerenkov-type configuration we can generate light down to a wavelength of 410 nm. Gratings as well as prisms were used to couple the fundamental beam into the waveguide.

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.

Phase-matched Frequency-doubling in Langmuir-Blodgett Film Waveguides Using the Cerenkov-type Configuration

ABSTRACT We demonstrate phase-matched frequency-doubling in Langmuir-Blodgett film waveguides of 2-docosylamino-5-nitropyridine (DCANP). The largest nonlinear optical coefficient d33 could be used by exciting TE modes propagating in the film. Using the Cerenkov-type configuration we can generate light in the absorption region of DCANP (at least down to λ = 410 nm where d33 = 27 pm/V, longest wavelength absorption maximum at λ = 380 nm). Conversion efficiencies of up to η meas conv = P2ω/Pω = 2·10−3 were measured (power Pω inside of the film) which is in agreement with the theory. Conditions for further optimization of the frequency-doubling efficiency are evaluated. Using a substrate material with optimized dispersion of the refractive index and a strip-waveguide geometry (width Wstrip = 2 µm) a conversion efficiency of η meas conv ∼ 10%W−1cm−1 could be obtained at a fundamental wavelength of λ = 795 nm.