SBIR-STTR Award

The highly directional properties of lasers makes them effective weapons when they are directed at the human retina or other sensitive detectors. Lasers are becoming increasingly more reliable, smaller and of lower cost. The recent introduction of practical low-cost tunable lasers circumvents any simple effort to obtain protection by using simple filters. The proposed polymers will contain one or more covalently attached ligands that work cooperatively to transfer charge between them (birchromophore). The net effect is to convent a virtually transparent polymer into a highly absorbing one. An extremely large change in absorption has been demonstrated in solution by chemically reacting similar species with strong oxidants. Our goal I this effort is to prepare a class of polymers containing donor species (strong absorbers) with one or more charge acceptors to facilitate a rapid and reversible absorption change which would protect human eyesight or other sensitive detectors. This approach can utilize different donors and acceptors can utilize can be used to obtain broadband protection. The Workplan involves the synthesis of several polymers followed by their chemical an optical characterization. LPT will make a special effort to develop a structure-function relationship using computational and measurement techniques.

Laser now manufactured are relatively inexpensive, rugged and wavelength tunable, making them a serious threat to human vision and the operation of sensitive optoelectronic sensors. While a great deal of effort has been invested in the development of Optical Power Limiting (OPL) materials operating by a number of different mechanisms that can provide protection against pulsed laser threat, few practical solutions exist. LPT has demonstrated in Phase I that a new class of polymers can offer OPL at a multitude of wavelengths and at the picosecond timescale. These materials function by photoinitiated charge transfer (which results in dramatic changes in absorption), but also exhibit two photon absorption (TPA) and are not only bichromophoric, but also bimechanistic. These events will occur at different wavelengths thus offering broader wavelength coverage than most OPL materials. Phase II proposal targets the development of polymers containing one or more pairs of charge donors and acceptors. Theroretical calculations on these compounds will establish useful structure-property relationships and provide a synthetic guide. A number of spectroscopic measurements will be made to determine optimum performance and elucidate the mechanism(s) responsible. the polymers will be cast as gradient films in anticipation of their use in practical systems.

Keywords:
lasers charge transfer bipolarons polymer polarons optical power limiting