Donald O. Frazier

Synthesis and characterization of various Schiff bases for non-linear optical applications

A series of salicylidenes have been synthesized to investigate non-linear optical properties. Attempts have been made to correlate second harmonic generation properties of these Schiff base compounds with ring substitution patterns, as well as the nature of the ring substituents. The result of double substitutions to the aniline moiety is also discussed. It is reported that meta substitution in the aniline moiety gives comparable values for second harmonic generation with respect to urea.

Observations of a monotectic solidification interface morphology

Abstract For detailed studies of the region around a solidification interface on a microscopic scale, a very thin (essentially two-dimensional) test cell may be translated across two temperature-controlled heating/cooling blocks and viewed with a microscope. Such a device is sometimes referred to as a temperature gradient microscope stage (TGS). Of particular interest in this study is the behavior of a monotectic type solution during solidification. Succinonitrile based model systems for metallic monotectic alloys, when solidified on a TGS, form an unusual “worm-like” micromorphology. These interfaces are observable in situ under high optical magnification during growth.

An all-optical picosecond switch in polydiacetylene

A polydiacetylene derivative of 2-methyl-4-nitroaniline (PDAMNA) showed a picosecond switching property. This phenomenon was demonstrated by waveguiding a cw He–Ne laser collinearly with a mode-locked picosecond Nd:YAG laser at 532 nm through a hollow fiber coated on the inside with a thin film of PDAMNA. The Z-scan investigations of PDAMNA thin films revealed that the PDAMNA system is a three-level system and the switching is caused by excited state absorption of the He–Ne beam.

Systematic study of polymorphism in crystalline non-linear optical materials

Abstract Crystalline polymorphism is quite common for non-linear optical (NLO) compounds. During our studies of NLO materials we found several compounds that crystallize in two or more forms. We present a short review of our recent data on the crystalline polymorphism of NLO compounds. Among the compounds studied, we found examples of concomitant polymorphism, induced conformational polymorphism, and organic polytypism. For several compounds, X-ray data are discussed along with computational data on molecular and crystal structure energy.

A redetermination of the succinonitrile-water phase diagram

The phase diagram of the water/succinonitrile system often used in modeling binary metallic alloys is determined experimentally using a laser scattering method. Triply distilled and zone-refined succinonitrile is placed in a jacketed water-cooled vessel with a magnetic mixer and a copper-constantan thermocouple, and the melting point is determined under vacuum and under Ar by observing the response of a photodiode placed opposite a laser source as the chamber is cooled and reheated. Then water is added, and the eutectic and monotectic temperatures and the entire phase diagram are determined under Ar. The results are presented in a table and graph and compared to those of Schreinemakers (1897): significant discrepancies are noted and attributed to impurities in the succinonitrile used by Schreinemakers. The importance of accurate phase diagrams for modeling binary alloys is stressed.

Edge enhancement and edge-enhanced correlation with photorefractive polymers

We demonstrate a simple all-optical realization of programmable edge enhancement and edge-enhanced correlation using novel photorefractive polymers. We show that the higher non-Bragg order in a two-beam coupling scheme contains the edge enhancement of the object when placed in the path of one of the incident beams. Also, this arrangement provides a scheme for writing joint transform correlation dynamic holograms, which can be read by a third beam. The correlation is edge enhanced, and the correlation peak increases with the applied bias voltage. Numerical results without and with beam fanning are presented. Theoretical predictions are reconciled with experimental results.

Molecular modeling and experimental study of non-linear optical compounds: monosubstituted derivatives of dicyanovinylbenzene

Abstract A search for potential non-linear optical (NLO) compounds has been performed using the Cambridge Structural Database and molecular modeling. We have studied a series of monosubstituted derivatives of dicyanovinylbenzene as the NLO properties of one of its derivatives (o-methoxy-dicyanovinylbenzene, DIVA) were described earlier. The molecular geometry in the series of the compounds studied was investigated with an X-ray analysis and discussed along with results of molecular mechanics and ab initio quantum chemical calculations. The influence of crystal packing on the molecular planarity has been revealed. Two new compounds from the series studied were found to be active in the second harmonic generation (SHG) in the powder state. The measurements of the SHG efficiency have shown that the o-F-, and p-Cl-derivatives of dicyanovinylbenzene are about 10 and 20 times more active than urea, respectively. The peculiarities of crystal structure formation in the framework of balance between the van der Waals and electrostatic interactions have been discussed. The crystal morphology of DIVA and two new SHG-active compounds have been calculated on the basis of the known crystal structures.

Structure and morphology of phthalocyanine films grown in electrical fields by vapor deposition

Phthalocyanine (Pc) films have been synthesized by vapor deposition on quartz substrates, some of which were coated with a very thin gold film before depositing the Pc films. Electrical fields up to 6200 V/cm between a mech electrode and the substrate are introduced during film growth. These films have been characterized by X-ray diffraction and scanning electron microscopy. The molecular orientations and surface morphology of Pc films were changed under the electrical fields. The surface of these films grown without an electrical field shows whisk-like morphology. When films are deposited under an electrical field, a dense film with a flat surface is obtained.

Optical computing: need and challenge

Focusing on the reality and promise of optical computing.

Coarsening of three-dimensional droplets by two-dimensional diffusion: part I. Experiment

An experimental study of diffusional coarsening, or Ostwald ripening, in a liquid-liquid two-phase system is described. An experiment performed at its isopycnic point, 42°C, allowed observations for the long times required to investigate coarsening. A holographic technique was instrumental in this work. Holograms takenin situ permit investigation of details regarding both the influence of local environmental conditions on individual droplet size histories and measurement of global averages. This study utilized a 100 μm pathlength test cell. The discrete phase was nucleated on one wall of the cell. This configuration resembles island formation in thin film growth. Observation of Ostwald ripening over a period of 1×107 s (∼4 mo.) reveals that droplet number decays as t−0.733 and the average radius increases as t−0.247, in the asymptotic limit. This shows good agreement with theoretical predictions for diffusional growth of spherical caps on a two-dimensional substrate which is a valid approximation for the geometry of this experiment. Part I of this paper describes the experimental results. Part II discusses a numerical model for droplet growth in a comparison with the experimental results.