Markus Adameck

Scanning second harmonic microscopy techniques with monomode and near field optical fibers

Extending our scanning second harmonic microscopy (SSHM) technique for the detection of lateral orientational inhomogeneities in high field poled polymer films, we present results with considerably improved lateral resolution by using optical fiber technology. Two experimental setups for measuring the χ(2) susceptibility of thin films are introduced. The first setup uses a standard monomode infrared-fiber with 10 μm core that carries the coherent fundamental infrared wave to the surface of a poled polymer film (illumination mode). The generated doubled frequency wave behind the nonlinear optical sample is detected by a photomultiplier tube. In the second setup a lens focuses the fundamental wave into the poled film. The resulting second harmonic wave is coupled into a 2.5 μm single mode fiber. SSHM micrographs of high field poled nonlinear optical polymer films were obtained with lateral resolutions of <3.5 μm. SSHM was also realized with a scanning near field optical microscopy fiber in pick up mode.

Fast recognition method for metallic topographies by the three-color selective stereo gradient method

A machine-vision system for real-time classification of moving objects with highly reflective metallic surfaces and complex 3D-structures is presented. As an application example of our Three-Color Selective Stereo Gradient Method (Three-Color SSGM) a classification system for the three main coin denominations of Euro coins is presented. The coins are quickly moving in a coin validation system. The objective is to decide only from comparison of measured 3D-surface properties with characteristic topographical data stored in a database whether a coin belongs to one of the reference classes or not. Under illumination of a three-color LED-ring a single image of the moving coin is captured by a CCD-camera. Exploiting the spectral properties of the illumination sources, which correspond to the special spectral characteristics of the camera, three independent subimages can be extracted from the first. Comparison between these subimages leads to a discrimination between a coin with real 3D-surface and a photographic image of a coin of the same type. After the coin has been located and segmented, grey value based rotation and translation invariant features are extracted from a normalized image. In combination with template matching methods, a coin can be classified. Statistical classification results will be reported.

Analyzing lateral χ(2)-distributions of poled nonlinear optical polymer films

Electric field poling of nonlinear optical (NLO) polymer films at very high electric fields can lead to (chi) (2)- distributions with poor spatial homogeneity, making such films unsuitable for optical devices. We report on further improvements of our scanning second harmonic microscopy using scanning near field optic techniques and on result on scanning optically poled films. Using a scanning Kelvin microprobe, a 2D image of the charge and polarization distribution inside the polymer films can be obtained. Similarities between the charge image and the second harmonic image are observed and allow to analyze the casus of the (chi) (2)-fluctuations. By measuring poling currents through triple stack layers and simultaneously detecting the second harmonic response, the internal electric field inside the NLO-film can be determined. Amorphous SiC:H layers, which were obtained by plasma enhanced chemical vapor deposition, are shown to be suitable for optical buffer layers and for dielectric interface coatings.

Mapping of the lateral polar orientational distribution in second order nonlinear thin films by scanning second-harmonic microscopy (SSHM)

We present a novel nondestructive experimental technique for the determination of the lateral distribution of the polar order in second order nonlinear optical (NLO) thin films. The sample, which consists of a poled polymer film, is scanned through the focus of an infrared laser beam in a second harmonic generation (SHG) setup and the second harmonic intensity is monitored stepwise. In combination with a conventional electrooptic (EO) characterization it is possible to create an EO-coefficient map of the sample. The resolution of this mapping technique can be significantly increased by using high numerical aperture (NA) microscope optics for the illumination of the poled polymer. This method, for instance, allows the evaluation ofpoling inhomogeneities due to high field poling and field distortions at the edges ofpoling electrodes.