Search results for "harmonic"
showing 10 items of 984 documents
Three-dimensional object recognition by Fourier transform profilometry
2008
An automatic method for three-dimensional (3-D) shape recognition is proposed. It combines the Fourier transform profilometry technique with a real-time recognition setup such as the joint transform correlator (JTC). A grating is projected onto the object surface resulting in a distorted grating pattern. Since this pattern carries information about the depth and the shape of the object, their comparison provides a method for recognizing 3-D objects in real time. A two-cycle JTC is used for this purpose. Experimental results demonstrate the theory and show the utility of the new proposed method.
A new criterion for determining the expansion center for circular-harmonic filters
1995
A new criterion for locating the expansion center of circular harmonic filters is presented. The innovation consists in the use of the information provided by both the circular harmonic energy map and the peak to correlation energy map of the object to be detected. The choice of an expansion center with a high value of peak to correlation energy ensures a good discrimination capability of the filter. In addition, we choose a point which is a local maximum for the energy map. An improvement of the discrimination ability is obtained with respect to previous methods.
Real And Positive Filter Based On Circular Harmonic Expansion
1989
A real and positive filter for pattern recognition is presented. The filter, based on the circular harmonic (CH) expansion of a real function, is partially rotation invariant. As it is real and positive, the filter can be recorded on a transparency as an amplitude filter. Computer simulations of character recognition show a partial rotation invariance of about 40°. Optical experiments agree with these results and with acceptable discrimination between different characters. Nevertheless, due to experimental difficulties, the method is onerous for use in general pattern recognition problems.
Third-harmonic generation in optical microfibers: From silica experiments to highly nonlinear glass prospects
2012
International audience; Using optical microfibers, phase matching between different propagation modes allows for third-harmonic generation (THG). After detailing the relevant phase matching conditions and overlap integrals, we provide a comparison between THG effective efficiencies in silica and tellurite glasses. We also explain the relatively easy, wideband, conversion that we observe experimentally in silica glass microfibers, from 155 mu m to the green, by the geometry of the tapering region.
Second harmonic generation in self-assembled alternating multilayers of hemicyanine containing polymers and polyvinylamine
1995
Abstract Assembly of noncentrosymmetric multilayers is a facile technique for preparing noncentrosymmetric films avoiding electrical poling procedures and problems from subsequent relaxation of the induced orientational order. A maximum Xzzz of 13 × 10−9 esu was achieved for the assembly of up to six layers. Current problems are the long-term hydrolysation of the hemicyanine nonlinear optical chromophores and the reduction of polar orientation with increasing layer thickness.
Poling dynamics of an EO active material using parallel-plate electrodes
2017
We describe the sample preparation and experimental setup for second harmonic generation measurement of electro-optical (EO) chromophore/polymer system at the time of contact-poling. Different types of spacers for avoiding electric breakdown due to avalanche multiplication are compared. Electric field threshold values for second harmonic generation are observed in all samples.
Vibronic structure in triatomic molecules : The hydrocarbon flame bands of the formyl radical (HCO). A theoretical study
1998
A theoretical study of the vibrational structure of the math 2A′ ground and math 2A′ excited states of the formyl radical, HCO, and its deuterated form, DCO, has been performed. The potential energy surfaces have been computed by means of a multiconfigurational perturbative method, CASPT2. The computed geometries and the harmonic and anharmonic frequencies are successfully compared to the available experimental information. The vibrational intensities of the transition math 2A′↔math 2A′ have been computed both for absorption and emission. The results lead to accurate determinations of several structural parameters and some reassignments of the vibrational transitions of the so-called hydroc…
Molecular motion, thermal expansion, and phase transitions in paraffins: A model for polymers
2007
Owing to their simple chemical structure paraffins are generally regarded as representing a system which is especially suitable for a model study of the thermal behavior of oligomeric and polymeric solids. Extensive investigations on the properties of n-tritriacontane (C33H68) provide an example. For this system an identification of several types of motional mechanisms become possible. Their presence leads to peculiarities in the thermal expansion and to the occurrence of solid-solid phase transitions. Paraffins and polyethylene exhibit a marked anisotropy in the lateral thermal expansion. An analysis of the molecular background can be based on a modified Gruneisen theory which connects exp…
Osmotic pressure, atomic pressure and the virial equation of state of polymer solutions: Monte Carlo simulations of a bead-spring model
1994
A recently introduced coarse-grained model of polymer chains is studied analyzing various contributions to the pressure as obtained from the virial theorem as a function of chain length N, temperature T and density ϕ. The off-lattice model of the polymer chains has anharmonic springs between the beads, but of finite extensibility, and the Morse-type interaction between beads is repulsive at very short distances and attractive at intermediate distances. Solvent molecules are not explicitly included. It is found that the covalent forces along the chain (modelled by the spring potentials) contribute a negative term to the pressure, irrespective of temperature, which vanishes linearly in ϕ as ϕ…
Electron crystallography and organic materials with non-linear optical properties
1999
Results of electron microscopic studies of crystal structures of a number of bis-benzylidene cyclohexanones are presented. It is shown that some of these compounds are efficient crystalline non-linear optically active (NLO) chromophores with second harmonic generation (SHG) properties. Appropriately functionalized chromophores of this type can be used as a polycondensation comonomer to produce partly crystalline main-chain NLO-active polymers. Electron diffraction crystal structural data, obtained for very small crystals, allowed us to get reasonable estimations of macroscopic crystal NLO-coefficients, relating quantum-chemically calculated molecular first hyperpolarizability components to …