Kevin J. Whitcomb

Photon Antibunching in Small Clusters of CdSe/ZnS Core/Shell Quantum Dots.

Coincident photon histogram measurements of fluorescence antibunching via confocal microscopy correlated with atomic force microscopy were carried out on (i) individual CdSe/ZnS core/shell quantum dots (QDs), (ii) several well separated QDs, and (iii) clusters of QDs. Individual QDs and well separated QDs showed the expected degree of antibunching for a single emitter and several independent emitters, respectively. The degree of antibunching in small, compact clusters was more characteristic of a single emitter than multiple emitters. The antibunching in clusters provides strong evidence of nonradiative energy transfer between QDs in a cluster. A minimal phenomenological model of energy transfer gives reasonable quantitative agreement with the experimental results.

DOE in DOIS: a diffractive optic image spectrometer

One limitation of diffractive optical elements (DOEs) or zone plate lenses is abundant chromatic aberration. A previous report described a novel system that exploits this typically unwanted effect to create an Image Spectrometer [Lyons 1995]. A DOE performs the imaging and provides the dispersion necessary to separate a multispectral target into separate spectral images. A CCD is stepped or scanned along the optical axis recording a series of these spectral images. This paper reports on the DOE that was fabricated, simulated and implemented in a visible DOIS prototype. The data from this prototype can be interpolated to predict the performance of fieldable DOIS systems that can be designed to operate at ultraviolet, visible or infrared [Hinnrichs 1995] wavelengths for multispectral and hyperspectral imaging in medicine, forensics, industrial and environmental monitoring, as well as military applications.

Characterization of the DOIS prototype: a diffractive optic image spectrometer

A diffractive optic image spectrometer has been designed and prototyped. Three dimensional spectral/spatial DOE imaging theory has been developed to simulate DOIS performance. The systems point spread function has been theoretically modeled and experimentally determined. The prototype has been characterized and demonstrated with a variety of targets. Three deconvolution algorithms have been implemented with the experimental 3D OTF and applied to recorded target images. The results shown demonstrate the high resolving power available with this approach.

Correlating structure and fluorescence dynamics of quantum dot clusters using super-resolution imaging

Clusters of quantum dots exhibit fluorescent behavior that differs from that of individual particles. Bulk measurements involving a large number of particles obscure these dynamics. Synthesizing clusters with 5–10 particles enables the study of collective behavior where single-molecule fluorescence techniques can be applied. Super-resolution microscopy of these clusters correlated with SEM imaging reveals the influence of geometry and structure on emission dynamics. Signatures of energy transfer can be seen in the form of enhanced blinking. Motion of the emission center of the cluster is tracked, made possible by the independent blinking events of the individual particles. Discrete steps in the localization are observed as random switching between various on/off configurations moves the location of the emission center.

DOIS: a diffractive optic image spectrometer

This paper will detail the basic characteristics and performance of a diffractive optic imaging spectrometer (DOIS). Diffractive optical element technology combined with a conventional CCD camera produces an elegant configuration for adding spectroscopy capabilities to current imaging systems. Its resolution rivals that of competing technologies, capable of hyperspectral resolution when used along with basic image processing techniques. DOIS is a rugged, economical, programmable, practical image spectrometer that can be adapted for use in visible, infra- red, and ultraviolet spectra for a multitude of applications.

Image reconstruction algorithms for DOIS: a diffractive optic image spectrometer

The diffractive optic imaging spectrometer, DOIS, is a compact, economical, rugged, programmable, multi-spectral imager. The design implements a conventional CCD camera and emerging diffractive optical element (DOE) technology in an elegant configuration, adding spectroscopy capabilities to current imaging systems (Lyons 1995). This paper reports on the visible prototype DOIS that was designed, fabricated and characterized. Algorithms are presented for simulation and post-detection processing with digital image processing techniques. This improves the spectral resolution by removing unwanted blurred components from the spectral images. DOIS is a practical image spectrometer that can be built to operate at ultraviolet, visible or infrared wavelengths for applications in surveillance, remote sensing, law enforcement, environmental monitoring, laser communications, and laser counter intelligence.