Michael E. Sullivan

Multimodal multiplex spectroscopy using photonic crystals

Spatio-spectral transmission patterns induced on low coherence fields by disordered photonic crystals can be used to construct optical spectrometers. Experimental results suggest that 1-10 nm resolution multimodal spectrometers for diffuse source analysis may be constructed using a photonic crystal mounted on a focal plane array. The relative independence of spatial and spectral modal response in photonic crystals enables high efficiency spectral analysis of diffuse sources..

Spherical beam holograms for spectroscopic applications: Modeling and implementation

A new approach for analyzing spherical beam holograms is presented and tested. This method describes the diffraction effect in spherical beam holograms and its application in spectroscopy. The theoretical results are verified by experiments.

Qualitative demonstration of spectral diversity filtering using spherical beam volume holograms.

We investigate the feasibility of designing spectral diversity filters using spherical beam volume holograms. Our experimental results qualitatively show the separation of the information of different incident wavelength channels using spherical beam volume holograms. The major trade-off in using these holograms is between the degree of spatial spectral diversity and the number of allowed spatial modes (or the divergence angle) of the incident beam.

Longwave infrared (LWIR) coded aperture dispersive spectrometer

We describe a static aperture-coded, dispersive longwave infrared (LWIR) spectrometer that uses a microbolometer array at the detector plane. The two-dimensional aperture code is based on a row-doubled Hadamard mask with transmissive and opaque openings. The independent column code nature of the matrix makes for a mathematically well-defined pattern that spatially and spectrally maps the source information to the detector plane. Post-processing techniques on the data provide spectral estimates of the source. Comparative experimental results between a slit and coded aperture for emission spectroscopy from a CO(2) laser are demonstrated.

Role of recording geometry in the performance of spectral diversity filters with spherical beam volume holograms

We present experimental demonstrations of spectral diversity filters with spherical beam volume holograms for multimodal multiplex spectroscopy. Major properties of filters under diffuse-light illumination are discussed. The comparisons of spectral diversity between the transmission geometry holograms and the reflection geometry holograms are also studied. The results show that there is a trade-off between the degree of the spatial coherence of the source and the spectral diversity of the filter. We also conclude that the reflection geometry holograms have better spectral diversity and less sensitivity to the spatial coherence of the source.

Measurement-efficient optical wavemeters.

We describe a method for efficiently determining the wavelength of a monochromatic source and provide an experimental proof-of-concept. The photomeasurement efficiency for a wavemeter can be written as eta(N,q) = (1 + logqN)/m, where N is the number of spectral channels, q is the number of distinguishable output levels per photodetector, and m is the actual number of photomeasurements made. An implementation is developed that achieves a theoretical efficiency of eta(N,q) = 1. The proof-of-concept experiment achieves efficiencies eta = O(1), where the deviation from theory is attributable to well-known optical effects and should be correctable in future versions.

Implementation of spectral diversity filters using spherical beam volume holograms

We present experimental demonstrations of spectral diversity filters using spherical beam volume holograms. Major properties of filters under collimated and diffuse light will be presented. We also show rotation multiplexing can improve the spectral diversity.

High-contrast, fast-switching liquid-crystal-on-silicon microdisplay with a frame buffer pixel array

A 64 x 32 liquid-crystal-on-silicon (LCOS) microdisplay with a frame buffer pixel architecture is described. The advantage of frame buffer pixel circuits is an increase in brightness and image contrast ratio. The increase in brightness is attributed to maximizing the overall image viewing time, allowing an image to be displayed at full contrast while the next image is loaded onto the pixels. The LCOS microdisplay employs a fast-switching optically compensated birefringence mode that operates at a 720-Hz frame frequency with a potentially high contrast ratio.

Diffuse spectroscopy for inhomogeneous metal nanoparticle assays

We describe a compact computational spectroscopy platform optimized for molecular recognition using metal nanoparticle assays. The objective is motivated by the urgent need for low-cost, portable and high-throughput sensors for point-of-care (POC) clinical diagnostics. Nanoparticle based sensing has been successfully demonstrated for diagnosis and monitoring of infectious diseases, drug discovery, proteomics, and biological agent detection. Molecular binding on the nanoparticle surface is transuded into an optical signal by modification of the nanoparticle extinction spectrum (via a shift in Localized Surface Plasmon Resonance) or by modification of the molecular scattering spectrum (via Surface Enhanced Raman Scattering). Translating a nanoparticle -based molecular recognition system into a functional miniature hand-held biosensor requires spectrometer designs optimized to large area nanoparticle assays and integrated spectral filtering to improve the signal specificity. Large population sampling with small population sensitivity is essential to highly sensitive nanoparticle assay analysis. We describe a multimodal multiplex spectroscopy (MMS) platform that samples the spectral response of up to 106 populations of 10-100 nanoparticles in parallel. The advantages of MMS approach include: extremely high signal throughput due to its large aperture and high resolution with small form factor. We will demonstrate a nanoparticle biosensor platform based on MMS. Ultimately, a fully integrated functional miniature nanoparticle based biosensor for real time disease diagnosis in whole blood assays can be realized.

Multimodal, Multiplex, Raman Spectroscopy of Alcohol in Diffuse, Fluorescent Media

Optical diagnostics in biological materials are hindered by fluorescence and scattering. We have developed a multimodal, multiplex, coded-aperture Raman spectrometer to detect alcohol in a lipid tissue phantom solution.