A two-color quantum-entangled photon source is used to produce fourth-order interference. Because the period of the interference is produced by the frequency difference of the entangled photons, problems associated with counting fringes can be avoided. This also permits measurements at a virtual wavelength, which can prevent problems associated with transmission or absorption when such a longer wavelength may be needed. The interference wavelength can be varied with a geometry change in the beam path without any change in the source wavelength. The entangled photons are produced using an argon ion laser at 351 nanometers and a type I BBO crystal. The interference is detected in coincidence using four photomultiplier tubes.
Liquid-nitrogen cooled quantum-well infrared photodetectors (QWIP) provide high response and high-speed detection of 10-micron radiation. When processed with high doping, QWIP's have been found to provide sensitive detection for long-wavelength infrared radiation at elevated temperatures. Experimental measurements using both direct and heterodyne detection show excellent performance at 10 microns and at temperatures up to 300 degrees-Kelvin. This high temperature operation allows applications in small or power limited platforms and significantly reduces the cost of the infrared detection system. Although only single element detectors have been evaluated, linear and 2-D arrays are expected to have similar performance characteristics. Experimental results for both video and heterodyne detection will be presented.
A design for an optical seeker optimized for spin-stabilized projectiles is presented. Using the spin of the bullet to scan a linear photodetector array across the target field, a relatively wide field-of-regard seeker may be constructed with an adequate SNR for homing applications. The linear photodetector array is based on room-temperature quantum-well infrared photodetectors (QWIP) optimized for a wavelength of 10.6 microns. The entire seeker containing the 1 × 64-element linear photodetector array, amplifiers and signal processor/flight computer can be constructed on a single 1-cm square bonded chip-on-chip. A compact folded telescope has been designed to collect light from a CO2 laser designator to guide the projectile to the target. Details of the seeker design as well as laboratory measurements of the concept using a visible light prototype seeker will be presented.
ORNL is developing a high-speed, full-duplex all weather communications link for ranges up to 5 kilometers. To accomplish this project, we have constructed an RF-driven waveguide CO2 laser and a dielectric-waveguide Stark modulator. The 10-micron wavelength was selected for its ability to penetrate smoke, fog, and rain. The modulator is based on the Stark shift of NH2D (deuterated ammonia). The laser is driven by a 60 MHz RF amplifier at a power level of approximately 50 watts. The resonator cavity of the laser is formed by a 2.4 mm internal diameter ceramic waveguide with external optics. The RF electrodes are formed from aluminum heatsink extrusions that also provide cooling for the discharge. Details of the laser design will be presented.
The Spallation Neutron Source (SNS) under construction at the Oak Ridge National Laboratory (ORNL) will be the most important new neutron scattering facility in the United States. Neutron scattering instruments for the SNS will require large area detectors with fast response (< 1 microsecond), high efficiency over a wide range of neutron energies (0.1 to 10 eV), and low gamma ray sensitivity. We are currently developing area neutron detectors based on a combination of a 6LiF/ZnS(Ag) scintillator screen coupled to a wavelength-shifting fiber optic readout array. A 25 x 25 cm prototype detector is currently under development. Initial tests at the Intense Pulsed Neutron Source at the Argonne National Laboratory have demonstrated good imaging properties coupled with very low gamma ray sensitivity. The response time of this detector is approximately 1 microsecond. Details of the design and test results of the detector will be presented.
Researchers at the Oak Ridge National Laboratory have been developing a method for measuring color quality in textile products using a tri-stimulus color camera system. Initial results of the Imaging Tristimulus Colorimeter (ITC) were reported during 1999. These results showed that the projection onto convex sets (POCS) approach to color estimation could be applied to complex printed patterns on textile products with high accuracy and repeatability. Image-based color sensors used for on-line measurement are not colorimetric by nature and require a non-linear transformation of the component colors based on the spectral properties of the incident illumination, imaging sensor, and the actual textile color. Our earlier work reports these results for a broad-band, smoothly varying D65 standard illuminant. To move the measurement to the on-line environment with continuously manufactured textile webs, the illumination source becomes problematic. The spectral content of these light sources varies substantially from the D65 standard illuminant and can greatly impact the measurement performance of the POCS system. Although absolute color measurements are difficult to make under different illumination, referential measurements to monitor color drift provide a useful indication of product quality. Modifications to the ITC system have been implemented to enable the study of different light sources. These results and the subsequent analysis of relative color measurements will be reported for textile products.
The Spallation Neutron Source (SNS) under construction at the oak Ridge National Laboratory will be the most important new neutron scattering facility in the United States. Neutron scattering instruments for the SNS will require large area detectors with fast response (< 1 microsecond), high efficiency over a wide range of neutron energies (0.1 to 10 eV), and low gamma ray sensitivity. We are currently developing area neutron detectors based on a combination of 6LiF/ZnS scintillator screens coupled to a wavelength- shifting fiber optic readout array. A 25 X 25-cm prototype detector is currently under development. Initial tests at the High Flux Isotope Reactor have demonstrated good imaging properties coupled with very low gamma ray sensitivity. In addition, we have developed a multi-layer scintillator/fiber detector to replace existing He-3 gas detector tubes for higher speed operation. This detector has demonstrated a neutron detection efficiency of over 75% at a neutron energy of 0.056 eV or about twice thermal. The response time of this detector is approximately 1 microsecond. Details of the design and test results of both detectors will be presented.
The high-speed production of textiles with complicated printed patterns presents a difficult problem for a colorimetric measurement system. Accurate assessment of product quality requires a repeatable measurement using a standard color space, such as CIELAB, and the use of a perceptually based color difference formula, e.g. (Delta) ECMC color difference formula. Image based color sensors used for on-line measurement are not colorimetric by nature and require a non-linear transformation of the component colors based on the spectral properties of the incident illumination, imaging sensor, and the actual textile color. This research and development effort describes a benchtop, proof-of-principle system that implements a projection onto convex sets (POCS) algorithm for mapping component color measurements to standard tristimulus values and incorporates structural and color based segmentation for improved precision and accuracy. The POCS algorithm consists of determining the closed convex sets that describe the constraints on the reconstruction of the true tristimulus values based on the measured imperfect values. We show that using a simulated D65 standard illuminant, commercial filters and a CCD camera, accurate (under perceptibility limits) per-region based (Delta) ECMC values can be measured on real textile samples.
New developments in 2-D, wide-bandwidth HgCdTe (MCT) and GaAs quantum-well infrared photodetectors (QWIP) coupled with monolithic microwave integrated circuit (MMIC) technology are now making focal plane array coherent infrared (IR) cameras viable. Unlike conventional IR cameras which provide only thermal data about a scene or target, a coherent camera based on optical heterodyne interferometry will also provide spectral and range information. Each pixel of the camera, consisting of a single photo-sensitive heterodyne mixer followed by an intermediate frequency amplifier and illuminated by a separate local oscillator beam, constitutes a complete optical heterodyne receiver. Applications of coherent IR cameras are numerous and include target surveillance, range detection, chemical plume evolution, monitoring stack plume emissions, and wind shear detection.