The measurement of absorbent concentration is a key control parameter in operating and assessing the performance of absorption heat pump systems. Because most refrigerant absorbent fluids are binary mixtures, the measurement of refractive index has been used routinely to directly determine the concentration of absorbent fluid components. Until recently, this measurement has been limited to the analysis of samples withdrawn from the absorption machine after system shut-down. The Fiber Optic Refrigeration Cycle Monitor (FORCM) is the first device capable of making multiple and in-situ, real-time measurements of refractive index at user-definable points within operating absorption machines. The refractive index of the solution is determined by measuring light loss from an unclad segment of an optical fiber that is immersed in the absorption fluid. Changes in fluid refractive index alter the angle at which the light rays are totally internally reflected at the core-fluid interface, thereby altering the light transmission efficiency of the fiber. The unclad portion of the fiber is placed at a point within the absorption vessel for which the fluid composition measurement is desired. Any number of modified optical fibers can be installed within a system. A thermocouple junction adjacent to each fiber measures the local fluid temperature. The combination of local concentration and temperature measurements allows in-line monitoring and control of the system, as well as provides a detailed study of heat and mass transfer processes occurring within these machines. The operating characteristics of the FORCM are described in this paper.

Fiber optic devices such as endoscopes have been in general use in the medical field for some time. More recently many doctors and instrument companies have begun developing fiber optic sensing systems and fiber optic laser power delivery systems to accomplish less traumatic surgery or localized irradiation treatment. These new systems are primarily single fibers rather than the coherent fiber bundles used in endoscopes, and thus the effects of the environments the fiber will encounter during fabrication/preparation, and during storage and use, must be considered more thoroughly. The changes arising from sterilization procedures and power delivery, specifically those associated with the fiber's strength and some of the effects related to optical degradation, will be discussed. Often the fiber must meet unique strength, fatigue and optical criteria to provide satisfactory performance in the particular medical application.

Different techniques to account for losses induced by the environment on signals in intensity modulation fiber optic sensing systems are described and analyzed.

Many industrial processes or other phenomena of interest cannot be measured with conventional instruments because they are too hot, too cold, highly radioactive, or other-wise inaccessible to direct observation. Nuclear wastes stored in underground repositories, for example, will require in-situ monitoring. A new technology that uses long distance fiber optics to transmit laser-excited fluorescence now makes it possible to remotely monitor such installations via optical fiber cables at distances up to one kilometer. The applications are listed below. - Sampling of remote locations - Multipoint sampling with single instrument - Measurements in inaccessible locations - Coping with aggressive environments - Avoiding contamination - Continuous monitoring

A four channel fiber optic radiometer has been built to measure the temperature and extent of reaction of a detonation before the shock wave destroys the collection optics. The system is designed to be calibrated both in terms of the relative radiant response and the absolute sensitivity of each channel. Fiber optics and associated data acquisition electronics allow synchronization of radiometric and pressure transducer signals to under 10 nsec.

Integrated optics have the potential to replace conventional electronics in many instrumentation applications; in many cases the integrated-optics approach is the only one that will achieve the necessary bandwidth and information-density goals. Thus far, has been done to address the prompt hardness of these devices to intense ionizing-radiation fields. We present preliminary data on the response of optical directional coupler modulators (ODCMs) to radiation from a Febetron. The Febetron produces energetic electrons in the 300-700 keV range in tilde 3-ns FWHM pulses, with a maximum dose rate of tilde 1014 rad/s. The operation of the ODCM is monitored during and promptly after the Febetron pulse impinges the device. Long-term effets are also monitored. These data are analyzed with respect to the operation of such devipes in a harsh inonizing-radiation environment.

Radiation-induced absorption in optical fibers has been a subject of considerable interest throughout the world 1,2. As availablility and applications of fibers have evolved from "first window" systems operating near 850 nm to "second window" systems near 1300 nm, interest in wavelength dependence of radiation effects in optical fibers has similarly evolved. Several recent studies have explored second-window radiation effects with both steady state measurements 3,4 and, to a limited extent, with transient measurements 5. No previous studies have explored the transient regime for times shorter than 10 μs. The present work summarizes second-window, radiation-induced transient absorption measurements in optical fibers for times shorter than 5 μs. Comparisons to first window data for these fibers are also presented. Only high purity silica fibers with low-OH concentrations were used in the present study to avoid the large OH absorption band in this region. This paper also collects first window data on several high-OH optical fibers. Preliminary data published previously are confirmed for one specific fiber type.

In previous papers, we have shown that the least radiation sensitive fibers are drawn from Fluosil and Diasil preforms and that the specific radiation response of these pure-silica core fibers is unequivocally determined by the test conditions. Here we demonstrate that the actual sensitivity levels of such fibers may differ by factors of up to 3-5 from charge to charge. Furthermore, we tested a pure-silica core fiber drawn from a new PICVD preform developed by Schott. This plasma impulse chemical vapor deposition process (PICVD) allows the production of preforms for pure-silica core fibers as well as for arbitrarily shaped graded index fibers doped with Ge or F. The new fiber compares favorably with Fluosil SW and Diasil type fibers, not only as regards the sensitivity levels but also the recovery characteristics.

Applications of rare-earth-ion-doped optical fibers to radiation sensing devices have been studied. It was revealed that rare-earth-ion-doped optical fibers are highly sensitive to radioactive rays such as gamma ray and thermal neutron flux and that they have little dependence on ambient temperature and optal power. An experimental distributed radiation sensing system incorporating Nd3+-doped optical fibers, radiation resistant optical fibers and an OTDR was made and tested. The results proved that the distributed sensing system is practically adaptable to the measurement of radioactive rays.

The effect of various coating materials on the total dose radiation sensitivity of 100/140 micron fluorosilicate clad, pure fused silica core step index fibers has been investigated. Various combinations of coatings allowed us to study the effects of coating type, coating thickness, single versus double dipped coatings, coating weight and coating cure intensity and duration. We find that the response of the fiber to Co-60 irradiation to 100 krads(Si) is influenced by the characteristics of the first coating deposited on the fiber, but is not sensitive to the second coating deposition. The most radiation resistant fiber was that coated with a polyimide, which is cured at a high temperature, while the least resistant was an acrylate coating cured by exposure to ultraviolet light. This result is fortuitous for space applications since the polyimide coating is also a low-outgassing, wide-temperature range coating material. We suggest that the variation in radiation response may be due to a post-drawing anneal occurring during coating cure which minimizes drawing-induced defects.

A set of both pure and doped silica core multimode fibers was irradiated in either pure gamma, pure proton, or mixed neutron-gamma irradiation fields. All parameters were maintained as nearly identical as practical so that a comparison of the effects of each type of irradiation could be made.

A very rugged, compact (3x3x10 inches), gas purged "PINHOLE CAMERA" has been developed for viewing electron beam materials processing (e.g. melting or vaporizing metal). The video image is computer processed, providing dimensional and temperature measurements of objects within the field of view, using an IBM PC. The "pinhole camera" concept is similar to a TRW optics system for viewing into a coal combustor through a 2 mm hole. Gas is purged through the hole to repel particulates from optical surfaces. In our system light from the molten metal passes through the 2 mm hole "PINHOLE", reflects off an aluminum coated glass substrate and passes through a window into a vacuum tight container holding the camera and optics at atmospheric pressure. The mirror filters out X-rays which pass through the AL layer and are absorbed in the glass mirror substrate. Since metallic coatings are usually reflective, the image quality is not severely degraded by small amounts of vapor that overcome the gas purge to reach the mirror. Coating thicknesses of up to 2 microns can be tolerated. The mirror is the only element needing occasional servicing. We used a telescope eyepiece as a convenient optical design, but with the traditional optical path reversed. The eyepiece images a scene through a small entrance aperture onto an image plane where a CCD camera is placed. Since the iris of the eyepiece is fixed and the scene intensity varies it was necessary to employ a variable neutral density filter for brightness control. Devices used for this purpose include PLZT light valve from Motorola, mechanically rotated linear polarizer sheets, and nematic liquid crystal light valves. These were placed after the mirror and entrance aperture but before the lens to operate as a voltage variable neutral density filter. The molten metal surface temp being viewed varies from 4000 to 1200 degrees Kelvin. The resultant intensity change (at 488 nm with 10 nm bandwidth) is seven orders of magnitude. This surface intensity variation is contrast reduced if the observation wavelength is a narrow band as far red as high intensity blooming will allow an observable picture. A three eyepiece camera allows an image plane where photo gray glass functions as a neutral density filter only over the high intensity portion of the image, thus reducing blooming. This system is enclosed in a water-cooled housing which can dissipate 15 watts/cm2, keeping the camera below 40 degrees Celsius. Single frames of video output are acquired for feature enhancement and location by a Data Translation DT2803 image processing board housed in an IBM PC.

The ATA is a 50-MeV, 10-kA, 70-ns pulsed electron beam accelerator that generates an extremely harsh environment for diagnostic measurements. Diagnostic targets placed in the beamline are subject to damage, frequently being destroyed by a single pulse. High radiation (x-ray, gamma, and neutron) and electromagnetic interference levels preclude placing components near the beamline that are susceptible to radiation damage. Examples of such components are integrated circuit elements, hydrocarbons such as Teflon insulation, and optical components that darken, resulting in transmission loss. Optical diagnostics play an important part in measuring experimental parameters such as the beam current density profile. A large number of optical lines of sight (LOS) are routinely deployed along the experimental beamlines that use the AlA beam. Gated TV cameras are located outside the accelerator tunnel, because the tunnel is inaccessible during operations. We will describe and discuss the difficulties, problems, and solutions encountered in making optical measurements in the ATA environment.

Extensive use is made of optical diagnostics to obtain information on the 50-MeV, 10-kA, 70-ns pulsed-electron beam produced by the Advanced Test Accelerator (ATA).1 Light is generated by the beam striking a foil inserted in the beamline or through excitation of the gas when the beamline is filled with air. The emitted light is collected and digitized. Two-dimensional images are recorded by either a gated framing camera or a streak camera. Extraction of relevant beam parameters such as current density, current, and beam size requires an understanding of the physics of the light-generation mechanism and an ability to handle and properly exploit a large digital database of image data. We will present a brief overview of the present understanding of the light-generation mechanisms in foil and gas, with emphasis on experimental observations and trends. We will review our data management and analysis techniques and indicate successful approaches for extracting beam parameters.

Precision measurements of the electron temperature and the electron temperature fluctuations in the Tokamak Fusion Test Reactor (TFTR) (major radius 2.6 meters, minor radius 0.8 meters, ion temperature 200 million degrees, electron temperature 70 million degrees) are necessary to understand the details of plasma stability and energy confinement. These measurements must be made remotely since there will be high radiation levels ( 1019 neutrons/pulse, 100 rads/pulse) as well as high levels of stray radiofrequency energy (50 MHz) and time changing magnetic fields in the vicinity of the tokamak. Three different instruments are used for these studies: a fast scanning superheterodyne radiometer (0.002 sec temperature profile); a fast scanning Michelson Interferometer (0.01 sec scan); and a twenty channel grating polychrometer which monitors electron temperature at twenty locations in the plasma continuously. The scanning radiometer uses state of the art mixers, detectors and levelers and must be heavily shielded from stray magnetic and radiofrequency fields, but is insensitive to neutrons and x-ray radiation. The Michelson system is relatively insensitive to radiation or stray fields. The grating instrument is located outside the 1.54 meter concrete shield wall to avoid a subtle neutron-detector interaction. Because of the large n, 4He inelastic cross-section (7 barns at 1.25 MeV), the neutron flux from the tokamak can perturb the temperature of the liquid helium bath used to cool the detectors. A temperature rise of several millikelvin is equivalent to a significant fraction of the temperature signal at the edge of the plasma. All three instruments may be calibrated absolutely and are designed for reliability and ease of maintenance.

A multichannel interferometer/polarimeter for the Tokamak Fusion Test Reactor (TFTR) has been developed in order to study the time dependent plasma current density (Jp) and electron density (ne) profile simultaneously. The goal of the TFTR is demonstration of breakeven via deuterium and tritium (DT) plasma. In order to be operated and maintained during DT operation phase, the system is designed based on the Michelson geometry which possesses intrinsic standing wave problems. So far, there has been no observable signals due to these standing waves. However, a standing wave resulted from the beam path design to achieve a optimum use of the laser power was found. This standing wave has not prevented initial 10 channel interferometer operation. However, a single channel polarimeter test indicated this standing wave was fatal for Faraday rotation measurements. Techniques employing 1/2 wave plates and polarizers have been applied to eliminate this standing wave problem. The completion of 10 channel Faraday rotation measurements may be feasible in the near future.

With a successful rocket-borne flight and instrument recovery, Utah State University and its contractors have demonstrated that its FT-IR interferometers are ideally suited for atmospheric research even under severe environmental conditions and at cryogenically cooled operational temperatures as low as 100K. In this presentation, issues of performance and calibration which are specific to FT-IR/detector interaction are highlighted. In April of 1986 a liquid helium cooled infrared Fourier transform spectrometer (FT-IR) was launched on a Talos/Castor rocket from the University of Alaska's Poker Flat Research Range. Figure 1 shows the rocket on its launcher during a test of the payload's pop-open clean shell. The sensor was designed, constructed and operated by personnel from Utah State's Stewart Radiance Laboratory. The telescoped earth-limb viewing spectrometer observed atmospheric night airglow backgrounds and an aurora 1,000 km downrange and returned infrared spectra from 2.5 to 22 um with spectral resolutions of 1 wavenumber and of 10 wavenumbers. More than 200 interferometric scans were taken during the eight minutes of flight and the outputs of five Si (As) detectors in the imaging focal plane were telemetered to the ground station. The instrument functioned flawlessly. Alignment and calibration were not affected by the rocket launch and only minor damage was found after parachute recovery even though the descent ended with an impact of greater than 30g. Currently the instrument is being recalibrated . The launch of the sensor extends a long line of successful ground based, aircraft borne, balloon-borne and rocket-borne FT-IR measurements made by Utah State University in cooperation with the Air Force Geophysics Laboratories. In this presentation, the complex flight hardware will be described briefly. Then, some specific issues relating to the relatively simple cyogenic imaging FT-IR sensor will be examined.

A cryogenic interferometer/spectrometer (FTIR) has been developed at Utah State University as part of the CIRRIS-1A experiment for flight aboard the space shuttle. The inter-ferometer has been configured to optimize its operation by a payload specialist who may not have experience with interferometry but has had payload-specific training. CIRRIS-lA incorporates an automatic sequencer which can be used to operate pre-planned measurement routines. However, a command and monitor panel in the orbiter allows the payload specialist to select which measurement routines control the experiment; it also displays system and subsystem monitor values on its CRT display. The specialist can actuate various internal calibration sources and monitor interferometer performance by viewing the resulting waveforms on a video monitor. An automatic alignment system is provided in case the interferometer needs to be realigned during flight. Detailed operational procedures have been developed to guide the specialist through planned measurement and malfunction procedures and will be flown as part of the payload flight data file to allow in-flight anomalies to be resolved with minimal aid from the ground.

An Air Force-sponsored effort to develop a versatile field sensor for the measurement of hydrogen chloride (HC1) vapors from rocket launches is described. Lawrence Livermore National Laboratory (LLNL) is developing an infrared HC1 detector with ppb range sensitivities to be used for monitoring HC1 during space vehicle launches at Vandenberg AFB. HC1 deposition on the community neighboring Vandenberg AFB can involve costly litigation. Monitoring is necessary to determine the amount of HC1 and if it presents hazardous situations or detrimental effects. The Air Force currently uses MIRAN IR sensors. These instruments analyze "grab samples" so they cannot accurately determine HC1 in a quickly changing atmosphere. Analysis times are on the order of several minutes, and there is no "real time" correction for background gases such as methane and water vapor. Sensitivity is only 3 ppm and remote operation is not feasible. The sensor developed by LLNL is an "in situ" sampler, which can constantly monitor a rapidly changing concentration of HC1 in air (response time is one second). It is a four-band differential absorption instrument, allowing for corrections due to system electronic and optical variations, as well as for variations in the background concentrations of methane and water vapor that also absorb at HC1 wavelengths. There is also the possibility of measuring HC1 droplets with this type of sensor. The detector's variable pathlength-absorption region allows for HC1 detection down to 200 ppb. The instrument is remotely operable, a necessity given the rugged Vandenberg terrain and limitations placed on personnel access to the launch area. The data from the battery-powered sensor are transmitted via radio link to a central base station where they are displayed and recorded using an IBM PC.

Low-power LASERs have been adapted for underwater use in order to solve a variety of measurement problems. Several systems, using HeNe plasma tubes, have been designed to determine range, measure size, and provide visual orientation information for photographic recording systems. Semi-conductor LASERs have been used for precise measurements of optical transmissivity and scatterance of seawater, in-situ. A number of applications will be described and future developments of these techniques will be discussed.

Cameras used to monitor underground nuclear testing experiments are subjected to a variety of harsh conditions which must be accounted for during the design phase. Since experiments are buried several thousand feet below ground, reliability is of foremost concern. Many of the cameras designed at Lawrence Livermore Laboratory contain coherent fiber optic components such as microchannel plate image intensifiers, fiber optic reducers, and diode or CCD imaging arrays. Coupling of these components calls for hardware which will maintain precise contact and alignment in conditions of high vibration, large thermal transition, and high humidity. In addition, the hardware must be easily assembled by untrained technical personnel under less than ideal conditions (windy, dusty, rainy, etc.). A high speed imaging camera based upon a Fairchild CCD array chip was designed at Livermore in 1984. Problems in coupling the array window to a fiber optic reducer were aggravated by mounting of the array chip rigidly to the main video circuit board. A new array chip daughter board, attached by flat ribbon cable and supported by a spring loaded lever combination was designed to overcome the problem. The hardware did not increase the overall size of the existing camera and increased the unit cost by less than 1 K$. The design of this hardware will be discussed along with useful techniques for designers of cameras used in harsh environments.