This PDF file contains the editorial “Editorial: Advice to authors” for OE Vol. 32 Issue 12

This PDF file contains the editorial “Guest Editorial: Magnetospheric Imagery and Atmospheric Remote Sensing” for OE Vol. 32 Issue 12

UVSTAR (Ultraviolet Spectrograph Telescope for Astronomical Research) is an EUV spectral imager intended as a facility instrument devoted to solar system and stellar astronomy. It covers the wavelength range of 500 to 1250 Å, with sufficient spectral resolution to separate atomic emission lines and to form spectrally resolved images of extended plasma sources. Targets include the lo plasma torus at Jupiter, hot stars, and planetary nebulae. UVSTAR will make useful measurements of emissions from Earth's atmosphere as well. UVSTAR consists of a pair of telescopes and concave-grating spectrographs that cover the overlapping spectral ranges of 500 to 900 and 850 to 1250 Å. The telescopes use two 30-cm-diam off-axis paraboloids having a focal length of 1.4 m. An image of the target is formed at the entrance slits of two concave grating spectrographs. The gratings provide dispersion and reimage the slits at the detectors, intensified CCDs. The readout format of the detectors can be chosen by computer, and three slit widths are selectable to adapt the instrument to specific tasks. The spectrograph package has internal gimbals, which allow rotation of ±3 deg about each of two axes. Dedicated finding and tracking telescopes will acquire and track the target after rough pointing is achieved by orienting the Orbiter. Responsibilities for the implementation and utilization of UVSTAR are shared by groups in Italy and the United States. UVSTAR is scheduled for flight in early 1995, timed for an opportunity to observe the Jovian system.

We constructed a high-resolution imaging spectrograph for use as a payload in a sounding rocket experiment. The spectrograph employs a modified Ebert-Fastie design with a LiF objective prism and a replica of an El echelle grating developed for the Space Telescope Imaging Spectrograph. The instrument has a 5-arcmin-long adjustable width entrance aperture with two identical secondary apertures separated from the primary by ±2 arcmin. The secondary apertures are intended for simultaneous measurement of the sky background. The spectrograph has been optimized for measurement of the 221st order of Lyman-α at a resolution of 0.03 to 0.04 Å. The detector system is a two-dimensional photon counting device that employs a microchannel plate intensifier and a wedge and strip anode readout. The spectrograph is used as a focal plane instrument of the Jupiter Telescope, a Cassegrain telescope constructed exclusively for use as a sounding rocket payload. The Jupiter Telescope is self-pointed, employing image motion compensation to achieve 2- to 3-arc sec image quality. The telescope/spectrograph payload was launched from the White Sands Missile Range on May 4, 1991, to observe the H Lyman-α line profile spatially resolved across the disk of Jupiter in the North-South (polar) and East-West (equatorial) directions, and to measure the H Lyman-α emission line profile from interplanetary hydrogen associated with the local insterstellar medium.

Monochromatic imaging instrumentation has been developed that uses narrow-band [12-Å full width at half maximum (FWHP)] interference filters or plane reflection gratings for 2-D imaging and imaging spectrograph applications. By changing the optics in front of the filter or grating, the field of view of the instruments can be varied from 180 deg (all sky) to 6 deg (narrow field). In the case of the 2-D monochromatic imager, the 12-mm-diam. filtered image is formed at ~f/1 on the input photocathode of an intensified CCD camera (380 x 488 pixels). Regardless of the field of view of the instrument, none of the rays passing through the filter exceeds 4.5 deg to the filter normal. In the spectrograph mode, a slit is placed on the field lens (at the focus of the objective lens) and the 4-in. interference filter is replaced with a reflection grating. The spectrum is imaged at f/1 onto the previously described detector with the spatial dimension of 380 pixels and the wavelength dimension of 488 pixels. The sensitivities of the systems are approximately 50 to 100 rayleigh seconds (Rs) (SNR~2). Examples of data taken with both of these instruments include detection and mapping of Jupiter's sodium magnetonebula and stable auroral red (SAR) arcs in the terrestrial ionosphere.

Japan's spacecraft PLANET-B will be launched to Mars in 1998. An extreme-ultraviolet (EUV) measurement of 30.4-nm wavelength is proposed for an interplanetary He⁺ observation during the cruising phase from Earth to Mars. This measurement will help our understanding of the creation and loss of interplanetary He⁺. Another objective is to image the plasmasphere and magnetotail of the Earth. The EUV scanner we have designed for the PLANET-B mission will provide the opportunity to observe both interplanetary and magnetospheric He⁺. In addition, we describe another improved design of this EUV scanner, which covers wavelengths from 30 to 90 nm. This improved scanner will measure scattered light from helium (58.4 nm) and oxygen ions (83.4 nm) in addition to He II.

When the Cassini spacecraft arrives at Saturn early in the next century it will carry an Ultraviolet Imaging Spectrograph (UVIS) designed and built by the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado. Observations made with the UVIS will support a broad set of scientific investigations including spectroscopy, imaging, and occultations. The UVIS consists of two spectroscopic channels covering the wavelength ranges 56 to 118 and 110 to 190 nm. Each channel has an off-axis parabolic telescope followed by a toroidal grating spectrograph and an imaging microchannel plate-CODACON detector. Mirror coatings and detector photocathode materials optimize the sensitivity of each channel for its particular wavelength range. Spectrograph entrance slit mechanisms provide three independent spectral and spatial resolution modes for each of the three channels. A third optical train consisting of a parabolic telescope and solar blind photomultiplier tube with a CsI photocathode provides a high-sensitivity photometer mode within the UVIS. The UVIS configuration was selected as a balanced solution to a large number of engineering and scientific constraints. We describe these constraints, the optical design, and the anticipated performance of the instrument.

We describe an instrument package to remotely measure thermospheric, exospheric, and plasmaspheric structure and composition. This instrument was flown aboard the second test flight of the Black Brant XII sounding rocket on December 5, 1989, which attained an apogee of 1460 km. The experiment package designed for this flight consisted of a spectrophotometer to measure He I 584-Å, O II 834-Å, a I 989-Å, hydrogen Lyman β (1025-Å), hydrogen Lyman α (1216-Å), and O I 1304-Å emissions, and a photometer to measure the He II 304-Å emission. The optical design of the spectrophotometer was identical to that of the Berkeley Extreme Ultraviolet (EUV) Airglow Rocket Spectrometer payload, flown on September 30, 1988, aboard the maiden flight of the Black Brant XII rocket. The He II 304-Å photometer consisted of a layered synthetic microstructure mirror tuned at 304 Å in a Wadsworth-type mount acting as a light bucket to focus incident radiation through a thin-film metal filter onto a channeltron detector. We also present the initial data analysis and describe directions we will go toward the completion of our study.

The Remote Atmospheric and Ionospheric Detection System experiment consists of eight instruments spanning the wavelength range from the extreme ultraviolet (55 nm) to the near infrared (800 nm) oriented to view the Earth's limb from the National Oceanic and Atmospheric Administration TIROS-J spacecraft to be launched into a circular orbit in 1993. Through measurements of the natural optical emissions and scattered sunlight originating in the upper atmosphere including the mesosphere and thermosphere, state variables such as temperature, composition, density, and ion concentration of this region will be inferred. The subset of instruments fabricated or otherwise provided by the Space and Environment Technology Center (formerly Space Sciences Laboratory) at The Aerospace Corporation are described.

Imaging of the earth's auroral regions in the ultraviolet provides information on a global scale on the energy flux and characteristics of precipitating particles and on the composition of the atmosphere in which the energy is deposited. We report the design of an imager with 0.6-mrad angular resolution over an 8-deg field of view sampled with 39,500 pixels, yielding global auroral coherent imaging from above 6 R_E(Earth radii). High-performance filters provide spectrally pure measurements of four key far-UV (FUV) features, with 5 x 10^-5 out-of-band rejection. Together with a solar blind intensified CCD detector, a net rejection of 10^-9 of all out-of-band emissions is achieved. The optical design comprises a three-mirror f/3 system that yields a noise equivalent sensitivity of 10 rayleighs (R) for a 37-s frame rate. The intrascene and interscene dynamic ranges are 1000 and 10⁵, respectively. The optical surface microroughness is less than 2 nm, providing exceptionally low light scattering characteristics, allowing simultaneous observations of very weak and bright emissions. The imager should provide about two orders of magnitude improvement in performance over previous designs.

The far-ultraviolet (FUV) imager for the International Solar Terrestrial Physics (ISTP) Mission is designed to image four features of the aurora: O I lines at 130.4 and 135.6 nm and the N₂ Lyman-Birge-Hopfield (LBH) bands between 140 and 160 nm (LBH long) and 160 and 180 nm (LBH long). We report the design and fabrication of narrowband and broadband filters for the ISTP FUV imager. Narrowband filters designed and fabricated for the O I lines have a bandwidth of less than 5 nm and a peak transmittance of 23.9 and 38.3% at 130.4 and 135.6 nm, respectively. Broadband filters designed and fabricated for LBH bands have the transmittance close to 60%. Blocking of out-of-band wavelengths for all filters is better than 5 x 10^-3% with the transmittance at 121.6 nm of less than 10^-6%.

As part of an ongoing investigation of airglow emissions of the upper atmosphere, an intensified CCD imaging spectrograph has been developed for a sounding rocket project called GEMINI (general excitation mechanisms in nightglow). The instrument, known as LISA (limb-imaging spectrograph for airglow), will be used to measure the limb profiles of some important nighttime airglow emission features. The observed limb profiles will be analyzed to provide atmospheric temperatures and density profiles of excited atomic and molecular species of interest to specific modelling problems in the mesopause and lower thermosphere. The GEMINI rocket is to be launched from White Sands Missile Range, New Mexico, in late 1993 or early 1994. The payload will be three-axis stabilized and absolute pointing will be derived from a star video camera. We describe the design capabilities of the LISA instrument, which include a spectral range of 310 to 390 nm, a wavelength resolution of ~0.3 nm, a height resolution of 1 km, and a theoretical count rate of 0.04 count R^-1 s^-1, where R represents rayleighs. The imager design is discussed and we present the results of some laboratory tests performed by means of an artificial source of the oxygen nightglow emission.

Direct measurements of energetic neutral atoms (ENA) and ions have been obtained with the cooled solid state detectors on the low-altitude (220 km) three-axis stabilized S81-1/ stimulated emissions of energetic particles (SEEP) satellite and on the spinning 400 km x 5.5 Re (where Re is Earth radii) Combined Release and Radiation Effects Satellite (CRRES). During magnetic storms ENA and ion precipitation (E>10 keV) are evident over the low-altitude equatorial region based on data from the SEEP (ONR 804) spectrometers and CRRES ion mass spectrometer (IMS-HI) (ONR 307-8-3) ion composition and ENA instrument. The MS-HI neutral atom spectrometer covers the energy range from 20 to 1500 keV with a geometrical factor of 10^-3 cm² sr and uses a 7-kG magnetic field to screen out protons less than about 50 MeV. During the strong magnetic storm of 24 March 1991 the first ENA and ion mass composition measurements were obtained of ring current partides below the inner belt and these fluxes are compared to the MS-HI flux measurements in the ring current. Recently, an advanced spectrometer, the Source/Loss-cone Energetic Particle Spectrometer (SEPS), has been developed to image electrons, ions, and neutrals on the despun platform of the POLAR satellite (~1.8 x 9 Re) for launch in the mid 1990s as part of NASA's International Solar Terrestrial Physics/Global Geospace Science (ISTP/GGS) program. To improve particle imaging by increasing sensor spatial resolution and sensitive area, a 256-element solid state pixel array having 6.25 cm² area has been developed for SEPS along with three new low-power application-specific integrated circuit (ASIC) microcircuits.

Magnetospheric imaging by remote detection of low-energy neutral atoms (LENA5) that are created by charge exchange between magnetospheric plasma ions and neutral geocoronal atoms has been proposed as a method to provide global information of magnetospheric dynamics. For LENA detection, carbon foils can be implemented to (1) ionize the LENAs and electrostatically remove them from the large background of solar UV scattered by the geocorona to which LENA detectors (e.g. , microchannel plates) are sensitive and (2) generate secondary electrons to provide coincidence and/or LENA trajectory information. Quantification of LENA-foil interactions are crucial in defining LENA imager performance. We present equilibrium charge state and angular scatter distributions for 1- to 30-keV atomic hydrogen, helium, and oxygen transiting nominal 0.5 μg cm² carbon foils. Results obtained after coating the exit surface of foils with either aluminum or gold suggest that the intended alteration of the exit surface chemistry has no effect on the charge state distributions due to foil contamination from exposure to air. Angular scattering that results from the projectile-foil interaction is quantified and is shown to be independent of the charge state distribution.

Techniques developed for the detection and characterization of energetic (>20 keV) ions in space plasmas have been modified to include imaging so that energetic neutral atoms at Saturn may be used to form images of the Saturnian magnetosphere and its interaction with the atmosphere of the moon Titan. The basic elements of the ion-neutral camera head on the magnetospheric imaging instrument for the Cassini mission are described, with emphasis on developmental detection techniques and components. In particular, pulse-height analysis of the microchannel plate responses to different mass neutrals is used for rough composition determination, and deflection plates in the aperture as well as time-of-flight measurements allow imaging of neutral atoms from within regions of moderate intensity ambient ion and electron fluxes.

A preliminary design for an imaging spectrograph that simultaneously covers the 2.15- to 5.2-μm spectral region with a resolution of 0.01 to 0.03 μm is described. The instrument is an extension to two dimensions of an existing infrared spectrograph that uses one-dimensional arrays of infrared detectors. In the two-dimensional version, light entering the spectrograph through a slit is dispersed onto a 256- x 256-pixel InSb array by a novel spherical-faced prism and mirror combination. The use of a prism rather than a grating disperser allows more than a one-octave spectral interval to be covered with no moving parts. In addition, the prism optical efficiency remains high over the entire band covered. The simplicity and ruggedness of the design make it ideal for a space-borne instrument.

We describe a possible sounding rocket payload consisting of an interferometer that would observe O I 1304-Å solar and airglow emissions simultaneously and a low-resolution (15-Å) extreme ultraviolet (EUV) spectrometer with a band pass between 250 and 1050 Å to measure the solar EUV flux, a primary source for the O I 1304-Å dayglow emission. The solar measurements, the first of their kind, could provide detailed information on the column of O along the line of sight of the instrument as well as information on the full disk solar line profile, which is important to planetary as well as cometary physics. The information gained through line profile studies of the dayglow includes the relative contribution of the two main excitation mechanisms, photoelectron impact and solar resonance scattering, and a means to verify cross sections and branching ratios. Furthermore, valuable information on optically thick cascade enhancement can be ascertained. All such information will substantiate sophisticated models, electron and radiative transport, that can be utilized in the remote sensing of the thermosphere.

Future space missions, large or small, that address planetary atmospheres should have the capability to observe occultations of the Sun by the atmosphere and to monitor the solar EUV and FUV flux. To be a viable candidate, the solar spectrograph must not compete with the primary experiments for mass and power. We have designed a compact solar spectrograph that covers the spectral range from approximately 200 to 3200 Å. It has no moving parts and records the entire spectrum within its range in a single exposure. The solar spectrograph is based on a classical Rowland grazing incidence design. Because of the intensity of the solar flux, small apertures offer adequate throughput. The spectrum is dispersed along the Rowland circle by three gratings and recorded in three side-by-side segments on a single detector, a CCD. The strong astigmatism in the grazing incidence design is canceled in the foreoptics. Control of stray light is a particular concern for a UV solar spectrograph, because of the extraordinarily large variation in the solar flux across the desired wavelength range. Techniques to minimize the effects of scattering include (1) suppressing it with appropriate coatings and optical components, (2) choosing a detector layout that permits measuring and subtracting the effects of scattered light from the spectrum, and (3) employing a photocathode that discriminates against long wavelengths. We estimate that a flight-ready unit would have a mass of about 1 kg and fit in a volume 20 x 9 x 7 cm.

New developments in transmission grating and photodiode technology now make it possible to realize spectrometers in the extreme ultraviolet (EUV) spectral region (λ<1000Å), which are expected to be virtually constant in their diffraction and detector properties. Time-dependent effects associated with reflection gratings are eliminated through the use of free-standing transmission gratings. These gratings together with recently developed and highly stable EUV photodiodes have been utilized to construct a highly stable normal incidence spectrophotometer to monitor the variability and absolute intensity of the solar 304-Å line. Owing to its low weight and compactness, such a spectrometer will be a valuable tool for providing absolute solar irradiance throughout the EUV. This novel instrument will also be useful for cross-calibrating other EUV flight instruments and will be flown on a series of Hitchhiker shuttle flights and on SOHO. A preliminary version of this instrument has been fabricated and characterized, and the results are described.

We are currently developing an instrument free from optical components to measure the full-disk solar spectrum in the extreme-ultraviolet (EUV) regime covering wavelengths from 75 to 400Å. The instrument consists of a windowless noble gas ionization cell followed by a toroidal electrostatic analyzer to spatially disperse photoelectrons as a function of their energies. A microchannel plate based position sensitive detector is used to detect individual electrons, indirectly returning the solar EUV spectrum. The instrument was launched aboard a NASA Black Brant sounding rocket on October 27, 1992. Power to this instrument was lost early in the flight, however, and a reflight is planned for October 1993. Calibration results for the He II 304-Å line are presented.

We describe a novel technique that enables us to conduct 2-D imaging spectroscopy with a 1-D imaging spectrometer. A typical imaging spectrometer obtains a series of 1-D monochromatic images that contain the entire field of view, but the spatial information in the dispersion direction is lost. By rotating the instrument (hence, rotating the field of view), we compile a series of time-dependent profiles. We use a numerical tomographic reconstruction method to recover the second spatial dimension and thereby obtain 2-D monochromatic images of the field of view. This technique is more sensitive and, hence, collects a full 2-D image more quickly than a conventional push-broom scan. We present the results of numerical simulations and discuss the prospects of this method for magnetospheric imaging applications.

Previously flown satellite imaging experiments have demonstrated the suitability of the VUV region for remote sensing observations of auroral particle precipitation. In the wavelength region 120 to 145 nm, a downward-viewing imager is uncontaminated by Earth albedo, and in most cases the intensity of auroral emissions is competitive with rescattered light even during daylit conditions. These features permit quantitative imaging of auroral regions during day and night conditions. An instrument was designed that has adequate wavelength resolution to separate key spectral features and simultaneously observe the Doppler profile of the auroral Lyman-or line. This instrument consists of an F3.8 Rowland circle spectrograph with a far-UV intensified COD at the focal plane. The spectrograph produces a 2-D spectral image where one dimension represents luminosity distribution and the other wavelength dependence. The UV intensified COD is programmed to pick up the luminosity distribution of various key spectral regions. The entrance slit is parallel to the spin axis and during rotation, a complete luminosity map of the region under the satellite is recorded. The proton velocity distribution will be studied by Doppler profile measurement of the Lyman-α line. A Hadamard grille is superimposed on the spectral slit and the Lyman-α data are deconvolved to obtain the required wavelength resolution.

The concept of using solar EUV line resonance scattering to image ion populations in the magnetosphere has been studied extensively in the last decade. Global magnetospheric EUV images can display the effects of scatterer density, injection, the geomagnetic field, and the changing perspective of earthshine source intensity with altitude, latitude, and local time. Successful use of these images for magnetospheric plasma diagnostics or for examining the morphology of the magnetosphere depends on properly accounting for these eftects and incorporating them into the models used to interpret such images. The importance of each of these effects is examined for varying levels of magnetospheric activity and different observer perspectives. Oxygen 834-Å resonance scattering is used as a testbed. A Tsyganenko 1987 magnetospheric model is employed to study the effects of different levels of magnetospheric activity. The resonance scattering formulation employed assumes an optically thin magnetospheric medium, with full inclusion of Doppler shift effects, for 834-Å radiation; Monte Carlo techniques are used for the construction of simulated magnetospheric images.

The measurement of neutral atom fluxes generated by charge exchange with the Earth's geocorona has recently been shown to provide the capability to image the magnetosphere. We investigate neutral oxygen fluxes produced by charge exchange from the cusp/cleft ion fountain population. Using an empirical cusp/cleft ion fountain model, an empirical variation of the geocoronal neutral hydrogen density with distance, and typical values for charge-exchange cross sections, line-of-sight integrations are performed to calculate the neutral oxygen flux at arbitrary locations in space. The resulting images are evaluated for a set of orbital positions of the proposed HI-LITE small explorer spacecraft. The resulting neutral oxygen fluxes are high enough for imaging with a low-energy neutral atom imaging instrument (ILENA) onboard the spacecraft.

By taking the atmosphere as an N-layer model and keeping the isoplanatic angle invariable for all the layers, the gain of the isoplanatic patch compared to the conventional adaptive optical system has been derived.

A balloon-borne x-ray pinhole camera has been developed to detect and image auroral x rays in the energy range 20 to 120 keV. We have flown this camera on four different occasions and have imaged bremsstrahlung x rays from precipitated energetic electrons in the auroral zone and from a circumpolar navigating balloon in Antarctica. The images, which include several dynamic precipitation temporal forms, show that auroral x rays persistently include small spatial structures of ≈2O km (at ionospheric heights). The x-ray energy spectral information as a function of space and time shows that electron precipitation often includes two energy components that can be fit by exponential functions. Typical e-folding energies of these spectra are a few kilo-electron-volts and several tens of kilo-electron-volts. The x-ray camera remote senses characteristics of energetic electron sources in the distant magnetosphere that cannot be achieved by any other means.

We describe the wide-angle geocoronal telescope (WIDGET). The telescope is designed to image resonantly scattered solar He-II 304-Å emission from the cold plasma constituent of the magnetosphere, the plasmasphere. It is a prime-focus telescope consisting of a spherical normal incidence f/2 mirror and a microchannel plate imaging detector. The instrument has a 30-deg field of view with a 0.5- to 1-deg angular resolution and a peak sensitivity of approximately 0.5 counts s^-1 rayleigh^-1 bin^-1. The instrument was flown on a sounding rocket on 27 October 1992 to test its capabilities. Unfortunately, no useful data were recovered due to a failure in the low-voltage system. (It was scheduled for reflight in October 1993.) WIDGET was designed so that it could easily be adapted to different wavelengths (584, 834, and 1216Å) by means of suitable mirror coatings and filters. In this way, a series of WIDGETs could image different aspects of the inner magnetosphere simultaneously, thus providing a more unified picture of this complex region.

This PDF file contains the editorial “Guest Editorial: Phase Contrast Microscopy” for OE Vol. 32 Issue 12

We present a review of the life and work of Frits Zernike (1 888-1 966), professor of mathematical and technical physics and theoretical mechanics at Groningen University, The Netherlands, inventor of phase contrast microscopy.

We present a review of the life and work of Frits Zernike (1 888-1 966), professor of mathematical and technical physics and theoretical mechanics at Groningen University, The Netherlands, inventor of phase contrast microscopy.

Phase object visualization problems of various spatial frequency filtration techniques and phase modulation depths are considered. The synthesis of the optical imaging is proposed as a solution, which consists in the separation of a part of the optical system (distorter) responsible for diffraction imaging perturbations. The imaging by the distorter is sufficient to formulate conclusions concerning the visualization problems of the phase objects. Using the vectorial interpretation of the phase object imaging, we show that the satisfactory choice of the visualization method depends on the phase modulation depth of an observed object; therefore, for an unknown phase object, it is necessary to dispose of a few different methods, simultaneously.

Properties and new possible applications of the slit phase contrast technique are presented. They are tested by an advanced computer simulation program. A digital 2-D spatial filtering process is performed. A composition of phase objects (e.g. , circles, rectangles, gratings, fibers) is transformed into its Fourier form, multiplied by the transmittance of the phase strip, and finally retransformed. According to the simulation results, several soot filters are prepared and applied to a modified commercial microscope. The experiments mainly involve biological specimens. Special attention is given to measurements of the refractive index profile of the optical fibers. A detailed theoretical background is presented and the results of additional computer simulation based on the operation of convolution are discussed.

In phase contrast microscopy there are various sources of unwanted stray light. Two that predominate in practice and are associated with the phase contrast technique itself occur when (1) the direct and the diffracted light cannot be completely separated by a phase plate (spatial filter) of a practically reasonable size and (2) the phase plate itself produces some light diffraction/scattering and reflections that diminish the sensitivity and imaging contrast of the phase contrast method. In the past, technological or engineering progress in conventional phase contrast instrumentation was mainly achieved by systematic reduction of stray light. An overview of this progress, supplemented by some unknown research results, is presented with an emphasis on the reduction of light reflections from the phase plate.

A simplified version of variable phase contrast microscopy of the polanret type is developed, It uses only a single polarizing ring instead of three zonal polarizers, as required in Osterberg's original polanret device. The polarizing ring is preceded (or followed) by a quarterwave plate and sandwiched between two rotatable polars (polarizer and analyzer).

Progress in modern light microscopy by means of new optic design and optical contrast-enhancement techniques [phase contrast (PhC), differential interference contrast (DIC), polarization, reflection] in combination with inverted microscopes and simultaneously with epifluorescence is described. Today, PhC and DIC optics are available for high-resolution light microscopy up to a numerical aperture of 1.4 (oil) as well as for long working distance optics mainly combined with inverted microscopes. The application of DIC facilitates high-resolution optical microscopy of living cell components, which can be isolated by selective micropreparation for extended microscopic analysis. The high contrast and the use of the full numerical aperture of the DIC optics make it possible to obtain a series of optical sections through rather thick living specimens. Optoelectronic techniques such as video-enhanced contrast microscopy and laser scanning microscopy in combination with optical contrast-enhancement methods are expanding into a new dimension that overlaps the low range of electron microscopy magnification but includes the use of living material.

The application possibilities of the phase contrast method in investigations of both isotropic and anisotropic optical fibers are discussed. In particular, this method enables the core diameter and other geometrical parameters of graded-refractive-index (GRIN) fibers to be determined more accurately when combined with scanning microdensitometry. The refractive index profile of some fibers, especially that of monomode fibers, can be determined by using a negative phase contrast device if the difference Δn between refractive indices of the fiber core and cladding is very small (smaller than 0.03). The result obtained is comparable to that offered by differential microinterferometry. In general, highly sensitive negative phase contrast microscopy, such as that based on the KFA device with soot phase rings (commercially available from the Polish Optical Works, Warsaw), permits us to observe extremely small optical inhomogeneities that cannot be revealed with the help of conventional microinterferometric techniques.

The possibilities of optical diagnostics of random phase objects are studied, based on measurements of transverse coherence function, scintillation index, and amplitude and phase dispersion of the field resulting from interaction with the object. The advantages of these methods over commonly used methods are increased speed and accuracy. Interference measurements of second- and higher-order correlation parameters of the field phase are demonstrated, which can be used to find the corresponding probability density distribution function for objects with phase statistics differing from Gaussian statistics. Also reported are results on the structure of phase-inhomogeneous crystals, rough surfaces, and plane-parallel plates.

Conventional test methods use optical switches for testing devices with large port counts such as couplers and splitters. These methods are both capital and labor intensive and cost between $250 and $300 per test channel. We describe a very reliable and low-cost approach for testing a large number of fibers by means of a mechanical indexer. The method not only reduces the setup time considerably but also offers significant savings in capital equipment. By means of this concept, a test system capable of testing 600 channels has been built at a cost of less than $50 per test channel.

The effects of spherical wave incidence on the microwave diffraction patterns of wavelength-sized gratings are shown and explained. These effects include broadening the angular width of each diffraction order; introducing extra phase differences between the adjacent periods; and, most significantly, inducing extra diffraction orders that would otherwise not exist were the incident wave a plane wave for the same grating. The existence of these extra diffraction orders is due to the range of angles of incidence caused by the spherical wave incidence. The diffraction patterns of wavelength-sized gratings for TE and TM polarization have very different characters. In particular, the TE specular components were saturated for an increasing depth of groove, while the TM specular components vary in a manner related to the depth-induced phase change at shallow depth; for deep-groove gratings, the TM components at backscatter were strong. It is believed that the far-field diffraction patterns are closely connected to the surface field distribution. The polarization dependence of the far-field diffraction patterns is explained in terms of the electromagnetic boundary conditions around the grooves. The strong TM components at backscatter are understood to be the result of multiple scattering.

The design and fabrication of a wide field-of-view (FOV) holographic lens for use in a laser communication receiver are described. The holographic lens was designed to image incoming laser radiation at 850 nm onto a solid state detector array over a FOV of ±22.5 x ±16 deg (±26.7 deg in the diagonal direction). Experimental results obtained with the holographic wide FOV laser receiver are presented. The location of the focused spot can be determined by interpolation to subpixel accuracy, providing the laser receiver with an angular resolution better than 1.5 mrad.

Diffraction gratings have been holographically fabricated on the "flat" surface of pre-etched D-fibers. The D-fibers are single mode with cutoff wavelengths of 633, 820, and 1300 nm. The gratings range in periodicity from less than 0.9 to 1.4 μm. Maximum total free-space coupling efficiencies of up to 82% are reported with a grating periodicity of 1.4 μm over a length of about 5 to 7 mm. Guided-mode to free-space coupling is enhanced by reducing the core-to-flat distance of the D-fiber. This distance is controlled by chemically etching the fiber by means of an in situ monitored etching technique. The different etch rates between the cladding and the silica cause a recessed contour in the cladding centered over the core. This recess causes difficulties when patterning submicron photoresist gratings over the core. Photoresist gratings are fabricated holographically by means of a Lloyd's mirror arrangement. Masked etching with hydrofluoric acid writes the gratings into the cladding structure of the fiber. Incorporating diffraction gratings into optical fibers miniaturizes integrated diffraction grating devices and eliminates the need to remove a signal from its fiber environment for processing.

Veiling glare is a phenomenon present in most imaging devices and systems. It is a source of concern in proximity-focused image intensifiers where it causes a loss in image contrast, especially at low spatial frequencies. Veiling glare was measured in two different ITT F4111 18-mm image intensifiers, one with a fiber optic input window and fiber optic output window (FO/FO), and the other with a quartz input and fiber optic output window (Q/FO), by means of a half-field high-contrast excitation method. Near-field veiling glare, a measure of stray light close to a high-contrast edge, and far-field veiling glare, a measure of more widely distributed stray light, were measured as fractions of the illumination level. Near-field veiling glare of 0.4±0.1 and far-field veiling glare of 0.08±0.02 were measured for the FO/FO intensifier, and near-field veiling glare of 0.38±0.01 and far-field veiling glare of 0.03±0.002 were measured for the Q/FO intensifier. The characteristic length, which is a measure of the extent of veiling glare from the edge, was 0.69±0.04 mm (near-field) and 1.8±0.4 mm (far-field) for the FO/FO intensifier, and 1.19±0.03 mm (near-field) and 6±1 mm (far-field) for the Q/FO intensifier. A preliminary investigation suggests that the characteristic length for near-field glare increases with increasing wavelength.

A computational framework for the flexible packing of arbitrary planar shapes under visual control is described. Our aim in this work has been to produce an efficient packing strategy that is flexible enough for a wide variety of industrial uses and which can be implemented in fast, moderately priced hardware. We have deliberately adopted a systems approach, versus a purely algorithmic one, since we are concerned with industrial vision problems in which significant problem constraints exist. The packing procedure that we devised consists of two major components. The first is a geometric packing technique that is based on morphological image processing operations. This is used in conjunction with a heuristic packing procedure. Some of the factors considered at the heuristic level include shape ordering and shape orientation, both of which must be carried out prior to applying the geometric packer. The heuristic procedure also deals with problem constraints that are specific to a given application. Various issues arising from this approach, such as the properties and performance of the procedure, are discussed within the background of some sample applications. The ideas outlined are currently being used in the development of a visually controlled intelligent packing work cell.

A procedure is described for the design of quadrilayer structures that enhance the polar Kerr effect in magneto-optic recording media. An essential feature of the method is a systematic approach that enables the achievement of phase optimization, which results in the elimination of the undesirable eftects of parasitic Kerr ellipticity. Examples are presented based on the Co/Pt superlattice and amorphous TbFeCo. The spectral and angular performances of fabricated devices are compared with theory.

We explore the application of adaptive (i.e., data-dependent) mathematical morphology techniques to range imagery, i.e., the use of structuring elements that automatically adjust to the gray-scale values in a range image to deal with (e.g., extract or eliminate) features of known physical sizes.

A miniature Vander Lugt optical correlator has been built to demonstrate this technology for guidance and navigation applications. Using a liquid crystal light valve as the input spatial light modulator, a cemented set of Porro prisms to fold the light path, and a combination holographic matched spatial filter and optical element, this rugged assembly is a prototype seeker head for an Army missile. The correlator is battery operated and mounts in a precision two-axis gimbal. The system correlates on aerial imagery and guides the missile to its preselected ground target. The correlator is 105 mm in diameter and 90 mm long. Including input optics, it weighs 2.3 kg.

The design of the polarizing optics of an instrument that uses laser tracking triangulation for the dynamic measurement of the 3-D coordinates of a retroreflective target is presented. The system, which uses dual-axis scanning mirrors, has applications in the performance testing and calibration of industrial robots. Analytical and experimental results are provided for the design of the polarizing scheme to maximize beam-energy usage for a given safety classification while minimizing any unwanted laser feedback and secondary beams that can affect measurement precision. Finally, a study of the depolarizing effects of air-path retroreflectors shows how severe degradation of measurement accuracy can result from their use in this context, which thus supports the alternative use of a cat's-eye type target.

Measurement of surface roughness by means of speckle technique has the advantage of being noncontacting and applicable to an in-process environment. Results from measurements of speckle contrast on ground surfaces are shown. The measurement range in the configuration used is Rq ≤ 200 nm. Comparisons of results between calculated and experimentally achieved speckle contrast are in agreement. An empirical method is presented that can be used to classify machined surfaces according to roughness when no specular component exists in the scattered light. The measurement range of this method is highly dependent on the machining process used. Surfaces with Ra ≤ 3.2 μm are classified according to roughness.

An optimized algorithm is proposed for the computer drawing of the envelopes of transmission and reflection spectra of a thin dielectric film on a transparent substrate. This allows the optical characterization of the film to be fully computerized using the two envelopes of a given spectrum. Optical characterization is performed for a model system by transmission and reflection spectra with noise for different film thicknesses. Computation is also made for an experimental transmission spectrum of an a-Si:H film on a quartz substrate. Higher consistency in the determination of the refractive index of the film n(λ) is achieved when it is calculated in the final step of the algorithm by the extremum condition and not by the two envelopes.

This PDF file contains the editorial “Book Rvw: Fiber Optic Communications," by Joseph C. Palais for OE Vol. 32 Issue 12