Blue Squaraine dye fluorescing a bright
pink under uv radiation from the
third harmonic of a picosecond
Nd:YAG laser.
 
 

One of two Nd:YAG laser used in
onlinear optical material studies at YSU
 
 

A view of the nonlinear optics lab
on a typically messy day.
 
 

Setup for photorefraction experiments.
 
 

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Current Research
Future Research in Non-Linear Optics

The widespread use of fiber optics in today's communications transmission systems is the first stage in a revolution of data processing and communications technologies based on optics rather than electronics. Current systems are expected to soon be drastically redesigned to include faster optical and hybrid optical/electrical components. 

The nonlinear optical (NLO) materials needed for optimized components , however, have not yet been realized. Basic research into the properties of candidate materials as well as applied research into the optimal use of these materials is greatly needed and is an important part of the activities here in the Nonlinear Optics Laboratories of the Program in Photon Induced Processes at YSU. These studies are directed by Dr. James H. Andrews of the Department of Physics and Astronomy. 

NLO polymeric and liquid crystalline materials have been identified as strong candidates for emerging photonic data processing technologies. These materials consist in general of molecular fragments displaying NLO activity, or highly colored chromophores, dissolved in or covalently attached to a polymeric host material. 

NLO polymers/liquid crystals possess vast potential for use in a variety of photonic systems, including high speed optical modulators, ultrafast optical switches, and high density optical data storage media. These devices are essential for continued advancement in the effort to transform information storage and transmission from the electrical to the optical regime. The promise of NLO polymers lies in their fortuitous combination of exceptional optical qualities, low cost, and ease of fabrication into device structures. This juxtaposition of technologically favorable characteristics has led to considerable research into the development of NLO polymers for commercial applications. A material suitable for widespread industrial use has yet to be synthesized, however. 

One of the most interesting and technologically promising phenomenon applicable to some of these materials is the light-induced modulation of the index of refraction of the material through the photorefractive effect. Photorefractive materials combine photoconductivity and the electro-optic effect. Photorefractive nonlinear optics is by far the most efficient technique for causing beams of light to interact. Holograms can be written and erased in photorefractive media with low power lasers, and the intrinsic phase shift in the holographic grating can lead to energy exchange between the writing beams. With the growing use of fiber optics and optical communications technologies, photorefractive materials have become prime candidates for all-optical data processing applications. They are expected to be used for high density optical data storage, associative image processing techniques including dynamic holography and image amplification, spatial light modulation, programmable interconnections in integrated optics and simulations of neural networks and associative memories with parallel signal processing. 

Polymers and liquid crystals have emerged in recent years as exceptional candidates for photorefraction, but much work in material development and characterization remains to be done. Our current research is intended to measure and model the mechanisms of charge generation, transport, and trapping in new classes of photorefractive polymers and liquid crystals. These experiments are critical to understanding the underlying mechanisms for photorefraction in these materials and to improving them for eventual commercial application. This ongoing research is a collaboration between YSU and researchers at Case Western Reserve University, and is supported at YSU by a Cottrell College Science Award from the Research Corporation. 

Anticipated projects in the nonlinear optics laboratories of YSU encompass the following goals:

To identify new nonlinear optical (NLO) materials as candidates for devices.

1.  To understand the nonlinear optical response of organic chromophores at the molecular level by probing the excited electronic states in the NLO materials that contribute most significantly to the nonlinear optical response. 

2.  To extend previous work on model NLO polymer/lliquid crystal systems to materials which are under current consideration for use in commercial photonic and optoelectronic devices, including optical modulators, optical switches, and optical storage devices based on the photorefractive effect. 

3.  To provide a state-of-the-art optical diagnostics laboratory for the characterization of the optical properties of materials developed through collaborations with chemists at YSU and other universities, at government labs, and in private industry, including novel organo-metallic chromophores. 

4.  To synthesize and characterize candidate NLO materials having organic and organometalic chromophores covalently attached and/or blended into polymeric materials. 

1.  To measure the photoconductivity, electro-optic coefficient, diffraction efficiency, and photorefractive two-beam coupling gain in novel multicomponent polymeric materials. 

2.  To identify ways to improve upon current photorefractive materials by studying the spectral response of current materials and the material response times and by varying the ratios of component materials to compare the effects of different functional groups. 

3.  To investigate the effect of different guided wave geometries on the speed and efficiency of the photorefractive response in NLO polymers, and the feasibility of such geometries in photorefractive optical memory devices needed to take advantage of the enhanced performance of all-optical information processing as compared to current electronic and magnetic technologies.