Diisocyanates are produced by the millions of tons per year and are used for the large scale production of polyurethane products that range from coatings, to solid castings, and to industrial foam products. Occupational exposure has been linked to asthma-like symptoms and is a significant occupational concern requiring personal monitoring devices for employees that are sensitive and accurate in the parts per billion range.
A novel design fiber optic chemical sensor has been developed which has demonstrated sensitivity of 0.2 ppb (parts per billion) for a 20 minute exposure in air for multiple isocyanate species. Sensor response is very linear over the range of 0 to 25 ppb. The sensor is based on a novel, long fiber, evanescent wave design that provides high sensitivity while maintaining low materials cost. Experimental performance results are presented, as well as a novel measurement approach that provides excellent linearity. Sensitivity to interference by humidity is modest.
Sensor packaging can be directly compatible for passive use in personal monitoring and the sensor us reusable. The sensor is simple and inexpensive to fabricate, and can be easy to process by the user in an automated instrument. Sensor processing is simple and is a nearly all dry process. The solid-state sensor can be packaged in a convenient size for personal monitoring. Highly quantitative sensor response is provided by a unique data analysis process that can be readily automated and provides high linearity over a range that is of direct applicability to sensing needs.
Through the introduction of a simply designed phase mask at the pupil of a conventional imaging system, the range to objects in view can be precisely determined. The mask allows for roughly 50% light transmission, and is segmented to introduce a 1/4 wave phase shift into half of the transmitted light. The resulting point spread function is highly sensitive to object range and is incorporated into the resultant image. Through comparison of the wavefront coded image with a conventional image of the same scene, the precise range to the object can be determined. The range measurement precision obtained is directly related to image contrast. For objects having a simple linear edge possessing a contrast of 32 gray levels above noise, range can be measured to 1% precision. While based on an interference effect, wide-band polychromatic light can be used to determine object range. No actively moving components in the optical system are required for operation. The resultant approach allows for imaging and range determination simultaneously. Based on a fundamental interference phenomenon, this approach is applicable to all passive optical imaging systems ranging from the UV to the infrared. Both a theoretical analysis and an experimental verification of the approach showing the expected performance is provided.
SPARTA has developed a novel dual wavelength interferometer which is directly aimed at stepper stage control and general IC metrology. It utilizes an existing HeNe based dual frequency interferometric system and couples it directly to a second system which provides the real time air turbulence compensation. The optical design provides for colinear optical beam paths for the two systems over the measurement path. Compensated position measurements are provided at a rate of 30 Hz which is sufficient to permit high throughput stage positioning for all modern steppers. Stage position accuracy is determined to 4 nm 3(sigma) and stage precision (which is a two pass operation) can be 5.6 nm 3(sigma) . Future improvements in performance can be expected since the present design is not near fundamental limits. The interferometric system design has a form factor compatible with existing stepper systems. Testing of this system has been carried out in a laboratory environment under a variety of conditions, including those which would simulate a clean room environment. Test results are used in detail and conclusions will be presented which define the impact this system can have on stepper overlay performance and IC metrology. Because the interferometer is the basic ruler upon which much of the stepper metrology, setup, and operation is based, an improvement in performance of this system provides numerous benefits in the areas of stage precision, alignment, lens metrology, and reticle qualification and fabrication. Furthermore, the elimination of air turbulence as a stepper design concern can permit improvements in stepper performance and throughput with fewer engineering compromises.
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.
This paper describes a new hardware architecture for searching and accessing data. This Content Addressable Memory (CAM) can be implemented using holographic storage in spectral hole burning media. The use of laser wavelength as a fourth dimension for volume holographic recording provides an additional addressing variable which can be used to advantage in a CAM architecture. This paper consists of three parts: definition of a CAM, presentation of two CAM concepts for digital data string and analog function search, and a discussion of architecture issues.
This paper describes the construction and operation of a 4D neural network computer. This demonstration system uses holographic interconnects recorded in a volume spectral hole burning medium. The paper provides an overview of the demonstration system and includes experimental details of components: the tunable laser, the detector arrays, the spatial light modulators, and preparation and cooling of the spectral hole burning medium. Experimental results showing association of image patterns and a bidirectional associative memory experiment are presented and discussed.
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.
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