Publications

Recent discoveries in the field of conjugated polymers in environmental stability, regiochemical regularity, and electrical conductivity, particularly of polythiophene and polyaniline, have intensified interest in device applications. Present or anticipated applications include development of electrical circuitry on a molecular scale, as well as conducting and semiconducting materials for a variety of applications including thin film transistors and batteries. The authors have investigated a series of compounds comprising conjugated segments coupled to photochromic elements. The photochromic reaction in these compounds reversibly alters the conjugation length and provides a mechanism for switching both the electrical and optical properties of these materials. The authors are currently investigating the nature and scope of this switching mechanism and preparing extended materials that take advantage of this novel form of switching behavior. Preparation and photochromic behavior of several of these materials are described.

We demonstrate that computer-generated diffractive optical elements can be used to synthesize the infrared spectra of real compounds. In particular, we describe a modified phase-retrieval algorithm that we have used to design diffractive elements of this type and we present experimental results for a diffractive optic which is capable of synthesizing the infrared spectrum of HF between 3600 cm{sup -1} and 4300 cm{sup -1}. The reflection-mode diffractive optic consists of 4096 lines, each 4.5 {mu}m wide, at 16 discrete depths relative to the substrate (from 0 to 1.2 {mu}m), and was fabricated on a silicon wafer using anisotropic reactive ion-beam etching in a four-mask-level process. We propose the use of such elements to replace reference cells in a new type of correlation spectroscopy that we call {open_quotes}holographic correlation spectroscopy.{close_quotes} Storage of a large number of diffractive elements, each producing a synthetic spectrum corresponding to a different target compound, in compact disk-like format, will allow a spectrometer of this type to rapidly determine the composition of unknown samples. Further, this approach can be used to perform correlation-based measurements of hazardous or transient species, for which conventional correlation spectroscopy is impractical.

We have measured the laser emission spectra of several vertical cavity surface emitting lasers following pulsed laser excitation, with a time resolution of < 1 ps. Correlations between the observed pulse widths and cavity lifetimes were observed.