This work demonstrates the feasibility of the evanescent field perturbation sensor approach for both three-dimensional and planar resonator geometries. An optical fiber-coupled silica sphere resonator and an integrated waveguide-ring resonator are used with a smaller sphere inserted in their evanescent tail. In both experiments, the motion of the perturber across the evanescent tail leads to a measurable shift in the resonators’ whispering-gallery-modes. The results show a consistent relationship between the mode shift and the position of the perturber.
The proposed sensor utilizes a whispering gallery mode (WGM) resonator to measure velocity-induced non-coherent Doppler shifts in Mie-scattered light from particles moving with the air-flow. The resonator replaces the typical Fabry-Perot instrument to measure the Doppler shift. A prototype sensor was developed and experiments were carried out in an atomizing nozzle with a 25μm-diameter water-droplet-seeded air jet. Individual velocity measurements were made at the center of the nozzle, switching the flow on and off. Preliminary results show promise for the WGM-based velocity sensor concept, which would significantly reduce the size and weight of future Direct-Detection-Doppler systems for air-speed measurement, with possible applications in airborne-platform weather-monitoring and planetary studies.
We present the test results of a neutron/gamma-ray imaging spectrometer for the identification and location of radioactive and special nuclear materials. Radioactive materials that could be fashioned into a radiation dispersal device typically emit gamma rays, while fissile materials such as uranium and plutonium emit both neutrons and gamma rays via spontaneous or induced fission. The simultaneous detection of neutrons and gamma rays is a clear indication of the presence of fissile material. The instrument works as a double-scatter telescope, requiring a neutron or gamma ray to undergo an interaction in two detectors to be considered a valid event. While this requirement reduces the detector efficiency, it yields information about the direction and energy of the incident particle, which is then used to reconstruct an image of the emitting source. Because of this imaging capability background events can be rejected, decreasing the number of events required for high confidence detection and thereby greatly improving its sensitivity. The instrument is optimized for the detection of neutrons with energies from 1-20 MeV and gamma rays from 0.4 to 10 MeV. Images and energy spectra for neutron and gamma rays are reported for several sources including depleted uranium and plutonium. In addition, the effect of neutron source shielding is investigated.
We present the design and development of a dual-species, neutron/γ-ray imaging spectrometer for the identification and
location of radioactive and special nuclear materials (SNM). Real-time detection and identification is important for
locating fissile materials. These materials, specifically uranium and plutonium, emit neutrons and γ rays via spontaneous
or induced fission. Co-located neutron and γ-ray emissions are a sure sign of fissile material, requiring very few spatially
correlated events for a significant detection. Our instrument design detects neutrons and γ rays from all sources in its
field of view, constructs images of the emission pattern, and reports the spectra for both species. The detection principle
is based upon multiple elastic neutron-proton scatters in organic scintillator for neutrons, and Compton scattering in
organic scintillator followed by photoelectric absorption in inorganic scintillator for γ rays. The instrument is optimized
for neutron imaging and spectroscopy in the 1-20 MeV range. We recorded images and spectra of a Cf-252 source from
0.5 - 10 MeV, and have done similarly for several γ-ray sources. We report the results of laboratory testing of this
expanded instrument and compare them to detailed Monte Carlo simulations using Geant4.
We have developed, fabricated and tested a prototype imaging neutron spectrometer designed for real-time neutron
source location and identification. Real-time detection and identification is important for locating materials. These
materials, specifically uranium and transuranics, emit neutrons via spontaneous or induced fission. Unlike other forms
of radiation (e.g. gamma rays), penetrating neutron emission is very uncommon. The instrument detects these neutrons,
constructs images of the emission pattern, and reports the neutron spectrum. The device will be useful for security and
proliferation deterrence, as well as for nuclear waste characterization and monitoring. The instrument is optimized for
imaging and spectroscopy in the 1-20 MeV range. The detection principle is based upon multiple elastic neutron-proton
scatters in organic scintillator. Two detector panel layers are utilized. By measuring the recoil proton and scattered
neutron locations and energies, the direction and energy spectrum of the incident neutrons can be determined and
discrete and extended sources identified. Event reconstruction yields an image of the source and its location. The
hardware is low power, low mass, and rugged. Its modular design allows the user to combine multiple units for increased
sensitivity. We will report the results of laboratory testing of the instrument, including exposure to a calibrated Cf-252
source. Instrument parameters include energy and angular resolution, gamma rejection, minimum source identification
distances and times, and projected effective area for a fully populated instrument.
Bacteriorhodopsin-based interferometry is a new technique with which high resolution interferograms can be recorded at one or more wavelengths in real time. The erasable nature of bacteriorhodopsin, its panchromatic response to light, and the fact that recording is done on the molecular level, allow for the formation of fringe patterns combining the high resolution of conventional silver halide recording materials with the real time properties of CCD cameras. In this context, we have used bacteriorhodopsin to image changes in the crystal environment at single and dual wavelengths, using a real time sequencing architecture whereby successive exposures of a bR thin film are overlapped to produce a continuous stream of interferometric images. This allows real-time data buffering and immediate, on-line observation of results. In this paper, we present real time single and dual wavelength interferograms of growing KAl(SO4)2 and melting sugar crystals recorded on bacteriorhodopsin thin films. The interferograms were produced with a shuttered cw argon or a pulsed Nd:YAG write laser, and a helium neon read laser, and show enhanced contrast and resolution. The results of this effort clearly demonstrate the superior, real time recording capabilities of bacteriorhodopsin thin films.
Electronic imaging of laser induced fluorescence from a plane of laser light that intersects a reactive flow is becoming commonplace. Quite often, the fluorescence wavelength is longer than the laser excitation wavelength and hence the fluorescence is easily discriminated from the Rayleigh and Mie scattering, which is at the laser wavelength. In the case of resonance fluorescence, the fluorescence is sufficiently near the laser excitation wavelength that low fluorescent signals are obscured by Rayleigh and Mie scattering. However, recognizing that the fluorescence scattering is weakly polarized while the Rayleigh scattering light is strongly polarized suggests that a polaroid filter could improve the signal to noise by eliminating Rayleigh scattered light and passing half of the fluorescent scattered light. By rotating the polaroid filter, any amount of Rayleigh scattering and resonance fluorescence from CH as it occurs in the flame front of premixed methane flames.
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