Philip D. Henshaw

Experimental demonstration of ultradense 4D holographic mass storage

This paper presents the results of a two-year Phase II SBIR program investigating a number of the key aspects of the use of Spectral Hole Burning media in a high capacity holographic optical digital computer memory. Factors which were experimentally examined include data longevity and unintentional erasure, and fundamental capacity issues relating to data densities and crosstalk. An experimental memory system was constructed and tested which had all the key elements of a digital memory system. Our experimental results confirm our previous analyses which indicate useful storage densities of 1012 bytes/cm3.

Atmospheric metrology using the air turbulence compensated interferometer

Air turbulence affects the performance of the helium‐neon interferometer used to control the wafer stage of stepper or step and scan lithography systems. In this article we describe the principles of operation and performance characterization of an air turbulence compensated interferometer (ATCI) designed to address these problems. Collinear combination of a two‐wavelength compensation system using second harmonic interferometry with the existing HeNe interferometer used for length measurement provides a highly accurate system with real‐time compensation for air turbulence. We characterized the performance of the ATCI system by measuring compensation performance in the presence of four different atmospheres.

Principal component analysis incorporating excitation, emission, and lifetime data of fluorescent bio-eerosols1

We describe a principal component analysis (PCA) of bio-aerosols which incorporates both fluorescence excitation-emission data over the excitation range 210 nm - 600 nm and lifetime data. The analysis suggests a useful separation metric based on spectral angle.

Background suppression and agent detection in multi-dimensional spaces

We describe a new method for background suppression and agent detection in principal component spaces derived from spectroscopic data to develop an improved trigger sensor for bioaerosol detection. Simulation results and laboratory data are shown.

Experimental implementation of an optical neural network scalable to very large size

This paper describes recent results obtained during the experimental development of a holographic optical neural network based upon the spectrally selective recording properties of spectral hole burning materials. This general architecture has been initially tested as a bi- directional associative memory system (a subclass of neural networks). The results obtained clearly demonstrate the fundamental ability to fully connect two 2D planes of digital information. Expectations are that this architecture can be extended to capacities of 1012 interconnects or greater in a modest form factor system.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Real-time stage position measurement with nanometer-scale accuracy

Air turbulence affects the performance of the Helium-Neon interferometer used to control the wafer stage of stepper or step-and-scan lithography systems. In this paper, we describe characterization and reduction of the major error sources in an Air Turbulence Compensated Interferometer designed to address this problem.

Genetic algorithms for unconventional imaging

Unconventional imaging techniques obtain high resolution images of objects at very long ranges without the use of large diameter primary optical elements. Cost and weight constraints lead us to consider methods for using sparse arrays of subapertures. In this paper, we present a genetic algorithm method for designing sparse arrays of subapertures for an unconventional imaging technique known as correlography. We have compared the solutions found using genetic algorithms to other techniques for generating arrays with filled autocorrelations. The results of this comparison are presented in this paper.

Applicability Of Laser Beamsteering For Rapid Access To 2D, 3D, And 4D Optical Memories

This paper discusses progress in device concepts for rapid access to data stored in optical memories. The paper reviews laser beamsteering and control techniques, optical memory configurations, and promising combinations for devices.

A fluorescent bio-aerosol point detector incorporating excitation, emission, and lifetime data

We present a novel approach to a biological point detector system: extracting maximal information from fluorescence by using as much of the full excitation-emission-lifetime (XML) fluorescence space as can be conveniently gathered. Our paper has two parts. In the first part, we present initial XML spectral data gathered under Phase I of the DARPA Spectral-Sensing of Bio-Aerosols (SSBA) program using a commercial laboratory spectrofluorometer and illustrate its analysis in a multi-dimensional Principal Components Analysis (PCA) data space. We demonstrate classification using the spectral angle (SA) methodology developed for hyperspectral imaging in this PCA hyperspace. In the second part, we present a design for a custom trigger sensor developed in Phase II of the DARPA program. This Phase II sensor was motivated by the Phase I results and is intended to exploit them by gathering XML data at a rate consistent with near-real-time triggering.

Stage accuracy results using interferometers compensated for refractivity fluctuations

Air refractivity changes, which include pressure, temperature, and composition effects, affect the performance of the Helium-Neon (HeNe) interferometer used to control the wafer and reticle stages of a step-and-scan lithography system. nanAlign is an auxiliary interferometer system designed to compensate for errors induced in a HeNe interferometer by refractivity changes. We conducted wafer exposure tests of nanAlign with 116 total wafers; 60 wafers with the same field order for each pass are discussed in this paper. We found that nanAlign measurements made on the x-axis could be used to improve the overlay in the y-axis. Over the entire ensemble of 60 wafers, the improvement of the x-axis was 0.6 nm, and the improvement of the y-axis was 0.4nm. Over the entire ensemble the worst wafers showed the most improvement, and there was some improvement on almost all wafers under a wide variety of conditions.