The use of rare gas halide lasers for generation of frequency conversion to the extreme ultraviolet is discussed. Experiments in third and fifth harmonic conversion of a XeCl laser are described. Areas of future progress are discussed.

Development of laser sources in the 200-400 nm region made little progress before 1975. This spectral region claimed only low power, low efficiency ion lasers, a few metal vapor cw lasers such as Cd, and the pulsed N2 laser at 337.1 nm. This latter laser had been the workhorse for dye laser pumping and other uv applications. It has been supplanted now by the rapid and remarkable development of rare-gas halide excimer lasers. These excimer lasers, using several rare gas-halogen mixtures, span the 200-400 nm spectrum with at least six major, lines. The gas mixtures have lent themselves well to electron beam, discharge sustained, and pure discharge pumping techniques. They can be made to emit up to 500 MW of peak power in pulses from < 100 ns to nearly 1 μsec and with 5-10% efficiency. These lasers appear to be scalable to become large energy devices. Concurrent with such a scale-up, however, must come more knowledge about such problems as the formation pathways, excited state and ground state kinetics, halogen donor replenishment, and damage problems with mirrors and other optical components at these short wavelengths. These new lasers have made a great impact in the 200-400 nm region. They are the lasers of choice for: up-conversion to shorter wavelengths to access the VUV; down-conversion to generate blue-green wavelengths; for pumping of dye lasers; and for photochemistry where good sources of photons have been in great demand.

High pulse repetition frequency, rare gas halide lasers are potentially useful in laser photochemical processes such as laser isotope separation. For practical use in many of these applications, high pulse repetition frequency operation must be achieved with good optical beam quality. Ideally, such a laser should achieve good medium optical quality with a minimum gas recirculation power. Component reliability in the laser cavity, flow loop and electrical circuitry is also needed for long laser lifetime. A closed loop XeCl laser, named Mistral, has been constructed at Mathematical Sciences Northwest, Inc., (MSNW), to investigate acoustic damping and flow control techniques needed to achieve good optical quality in these lasers. The device uses a 20 cm long UV preionized laser cavity to produce power levels of order 100 W. The flow loop has been designed to minimize flow disturbances and to allow examination of the performance of various acoustic dampers located in the side-walls of the flow channel upstream and downstream of the discharge region. A burst of laser pulses at 1 to 2 kilohertz PRF is provided by a main discharge triggered spark gap switched PFN coupled to 8 ft.-long cable peaking capacitors. The test time is limited by the gas capacity of the triggered spark gap gas supply to about 2 minutes. The loop is constructed primarily of nickel plated stainless steel, and includes a centrifugal blower and heat exchanger. A description of the design, fabrication and operation of this facility is given together with the results of current experimental investigations.

The device which is described thereafteris intended to measure the "in situ" oxidation-reduction state of a living tissue and is based on U.V. laser induced fluorescence.

The basic concept of plasma confinement in tokamaks is discussed and illustrEtions of the typical temperatures and densities that can be obtained are presented. The roles of impurities both as sources of power losses and as plasma diagnostics are emphasized. Particular attention is paid to the analysis of spectral data to obtain impurity concentrations, the deleterious effects of heavy metals, forbidden transitions, and spectral excitation by charge echange reactions.

Laser fusion involves the compression using very high power laser beams of a pellet containing fusionable fuel, such as a deuterium-tritium mixture, to such high densities and temperatures that it ignites and yields a net energy gain. The deposited energy causes a plasma to ablate from the target surface which drives the implosion. The physics issues to achieve success are numerous; they include: the laser absorption and pellet surface acceleration processes must be benign and efficient; uniform megabar pressures must be gen-erated by the ablating plasma to accelerate the target shell inward with a velocity over 150 km/sec and with about 1% accuracy; throughout this implosion the fuel must remain cold. To study these physics issues a number of novel diagnostics gre required. They involve measurements of photon and particle energies from 1 eV to 10 5 eV with subnanosecond time-resolution and micron spatial resolution. Many of these diagnostic techniques and their applications in the NRL laser fusion experiment are described.

Conventional vacuum ultraviolet line sources often consist of electrodeless rf or microwave discharges of flowing or sealed inert gases at 1-10 torr. The inert buffer, typically helium or argon, is seeded with traces of parent species of the desired transitions (e.g., 02 or N2 for OI or NI transitions, respectively). The sensitivity of resonance sources as absorption or fluorescence diagnostics depends critically upon the effective line width of the source resonance radiation. This property is determined primarily by source self-absorption, and by Doppler broadening of the source radiation, which is itself a function of the translational-energy distribution of the radiating species. Self-absorption is easily minimized or characterized experimentally. However, Doppler broadening is a complex function of the lamp excitation processes and should be characterized for each type of resonance lamp. The major competing excitation mechanisms for transitions such as 01 (130 nm) or NI (120 nm, 149 nm, 175 nm) in such line sources are electron impact processes, where the excess kinetic energy of the collision is retained with the electrons, and energy transfer or dissociative excitation by rare gas metastables (Ar(3P2,0) at 11.5 eV or He(23,1S) at , 20 eV), where a significant fraction of the energy defect may appear as excess translational energy in the radiating species. The kinetics of these processes as they relate to various VUV atomic line sources are reviewed. In addition, preliminary experimental data from absorption measurements on atomic nitrogen metastables, N(2D) and N(2P), produced in a discharge-flow apparatus, are presented which show markedly different behavior between microwave-excited He/N2 and Ar/N2 lamps. The implications of these effects for design application of resonance absorption/ fluorescence diagnostics are illustrated.

The use of electron accelerators as sources of synchrotron radiation for researches in a wide range of disciplines has grown enormously during the past ten years. Concurrent with this growth, the development of instrumentation capable of exploiting the unique properties of the synchrotron radiation from these sources has proceeded apace. It is therefore, useful to review the present "state-of-the-art" and to preview several very likely future developments in synchrotron radiation sources and instrumentation. Included in this presentation are descriptions of the sources and the radiation, examples of presently operating experimental systems and a discussion Wigglers, Undulators and Free Electron Lasers.

Synchrotron radiation is a source of continuum radiation ranging from the x-ray or soft x-ray region (depending on machine energy) to beyond the visible region. The amount of radiation emitted is a calculable function of machine operating parameters. This makes it possible to use synchrotron radiation from electron synchrotrons and electron storage rings as an absolute source particularly in the VUV and soft x-ray regions where other standards are difficult to find. At the National Bureau of Standards (NBS) an electron storage ring (SURF-II) has been used to calibrate spectrometers and photometers used in solar and aeronomy research and in fusion plasma diagnostics. A large chamber has recently been completed to facilitate such calibrations. The radiation incident on these spectrometers can be calculated to uncertainties of 3%. A technique to exactly determine the number of electrons orbiting in the ring is currently being developed to reduce this uncertainty. Detector calibrations between 5 - 55 nm are routinely carried out at SURF-II and transfer standard detectors with 6-10% uncertainties over the range of 5 - 254 nm are supplied. Special studies of "practical", high efficiency, and disposable photodiodes have been made by NBS in collaboration with other groups.

Electrons and positrons channeled in crystals traverse periodic trajectories which, as in an undulator, results in the emission of narrow band electromagnetic radiation. This radiation can cover the soft x-ray to y-ray portion of the spectrum, with the photon energy dependent upon the particle energy. In silicon, for example, with y = 100 where y is the ratio of the particle energy to its rest energy, forward-directed photon energies from planar-channeled particles are in the 20 - 130 keV range. The potential function for positrons trapped between crystal planes is nearly harmonic, so that the eigenvalues derived from this potential are approximately equally spaced and therefore result in a single emission frequency. Electrons are in a potential with an approximate exponential dependence upon coordinate, yielding multiple emission frequencies. Emission linewidths (full-width, half-maximum) have been predicted and measured to be in the 10 - 25% range. The important factors contributing to this linewidth are the finite coherence length for radiation, particle beam divergence, potential anharmonicity (for the case of positrons), energy spread of the particles, finite crystal thickness, and broadening associated with crystal periodicity (Bloch-wave broadening). For relativistic particles the emission is within a cone in the forward direction with half-angle y-1. The radiation is linearly polarized, and has an intensity that is up to an order of magnitude larger than bremsstrahlung for a randomly directed particle. The time structure of the radiation reproduces the time structure of the particle beam which, for our linear accelerator, is composed of 10 picosecond bursts.

Progress in the research devoted to developing x-ray lasers will be reviewed as it pertains to one-electron hydrogenic ions created and pumped to inversion in high-density laser-produced plasmas. A simple analysis defines a useful parameter space. Measured gain coefficients for C5+ are in good agreement with modeling for electron-capture pumping. Photon pumping is identified for possible circumvention of radiative-trapping limitations in larger volumes. Preliminary data on aluminum appear promising for shorter wavelength extrapolation. The advantage of efficient x-ray cavities is apparent. Extension of the illustrative analysis provides directions for future quantitative measurements leading to large scale gain experiments.

Characteristics of the generation and absorption of ultraviolet radiation and x-rays are examined for their effects on lithographic replication of tine scale features. Direct-write, projection, proximity and contact UV lithography are Drietly reviewed. Emphasis is given to x-ray lithography, especially the wide variety of potentially useful plasma x-ray sources. Reference is also made to other aspects of x-ray lithography, namely masks, resists and alignments, as well as full x-ray exposure systems.

This paper reports the current status of our program to develop far- and middle-ultraviolet-sensitive electrographic detectors. These include large-format, semitransparent-photocathode detectors and opaque-photocathode electrographic Schmidt cameras. Modifications of a previously-demonstrated far-UV large-format detector to make it suitable for possible Shuttle/Spacelab space astronomy investigations have been implemented and tested. Middle-ultraviolet-sensitive large-format and Schmidt electrographic detectors are now in the laboratory development stage. Cesium telluride photocathodes are used to provide sensitivity in the 1700-3100 A spectral range, and techniques for processing these photocathodes are discussed. The preparation and use of polyimide barrier membranes, for protecting the photocathodes from deterioration by film outgassing, are described. A new opaque-photocathode vacuum-ultraviolet-sensitive electrographic detector has been demonstrated, which is based on an oblique-focusing electron optical system similar to that used by Princeton with electron-bombarded CCD arrays. Test results and potential applications of this detector are described.

Development work is currently underway at Princeton and NRL on electronic-readout imaging detectors for the vacuum ultraviolet which are based on electron-bombarded CCD arrays and opaque alkali-halide photocathodes. These detectors provide single-photoelectron detection ability and wide dynamic range combined with nearly the maximum possible quantum efficiency (in excess of 50% in the wavelength range below 1300A •). The Princeton work is based on an oblique-focusing electron optical configuration. The NRL program is based on a Schmidt optical system with opaque photocathode as used previously with electrographic image recording. Thinned, back-surface-bombarded CCD arrays manufactured by RCA and by Texas Instruments are being used in the developmental devices. Results of preliminary tests at Princeton, and an overall system concepts for the Princeton and NRL cameras, will be discussed. Applications to possible space astronomy investigations will be described.

The Multi-Anode Microchannel Arrays (MAMAs) are a family of photoelectric photon-counting array detectors, with formats as large as (256 x 1024)-pixels that can be operated in a windowless configuration at vacuum ultraviolet (VUV) and soft x-ray wavelengths or in a sealed configuration at ultraviolet and visible wavelengths. In this paper, we describe the construction and modes of operation of (1 x 1024)-pixel and (24 x 1024)-pixel MAMA detector systems that are being built and qualified for use in sounding-rocket spectrometers for solar and stellar observations at wavelengths below 1300 A. We also describe briefly the performance characteristics of the MAMA detectors at ultraviolet and VUV wavelengths.

Two systems based on charge-coupled device (CCD) arrays have been designed and tested for image detection at vacuum ultraviolet wavelengths. A camera using a CCD in conjunction with a microchannel plate image intensifier was developed and qualified for space flight. A second camera system uses a thinned, back-illuminated CCD for direct detection of extreme ultraviolet radiation. A space qualified version of this camera is currently under development. Both systems produce images of excellent quality, with very high photometric sensitivity.

The fluorescence properties of coronene, liumogen and of acrylic films doped with organic laser dyes, and their application to silicon photodetectors are discussed. Photon conversion efficiencies have been measured in the VUV and UV range and from room temperature to 108 K. The fluorescence quantum efficiency of coronene was found to be ~60%, that of liumogen ~50% and for doped acrylic as high as ~95%. All three phosphors emit between 450 and 600nm, with emission peaks at 500nm for coronene, at 510nm for doped acrylic and at 520nm for liumogen. Their fluorescence efficiencies do not change with temperature and are essentially constant over wide wave-length ranges. On coated silicon photodiodes external quantum efficiencies of up to 20% have been obtained with coronene and liumogen. With acrylic films doped with organic dyes, effective quantum efficiencies are of the order of 15% for 120nm < X < 165 nm and ~40% for λ > 190 nm. Square wave response measurements on coated linear photodiode arrays indicate that the coatings do not adversely affect spatial resolution in the visible and near infrared. In the UV, however, spatial resolution is lower than at longer wavelengths.

Manufacturing, optical fibers to be used in the ultra-violet causes a certain number of particular problems. You must, as for all optical fibers, find two materials one for core, one for cladding.

The Space Telescope (ST), which carries two UV sensitive digicons, will ?ass several times per day througn a low altitude radiation belt called the South Atlantic Anomaly (CAA). This is expected to create interference in what is otherwise anticipated to be a noise-free device. Two essential components of the digicon, the semiconductor diode array and the UV transmitting window, have been shown by us to generate noise when subjected to medium energy proton radiation, a primary component of the belt. These trapped protons, having energies ranging from 2 to 400 HeV and fluences at the digicon up to 4000 P+/sec-cn2, will pass through both the window and the diode array depositing energy in each. To evaluate the effect of these protons, we irradiated engineering test models of digicon tubes to be flown on the ST with low-flux (104 10 P+/sec-cmz) monoenergetic proton beams at the University of Maryland Cyclotron. It was shown that electron-hole pairs produced by the protons passing through the diodes or the surrounding bulk causes a background count rate exceeding previous estimates by a factor of between 5 and 10. It was also shown that these counts can occur simultaneously in the output circuits of several adjacent diodes. Pulse height spectra of these proton induced counts indicate most of the bulk related counts overlap the single photoelectron peak.

The International Ultraviolet Explorer (IUE) was launched January 26, 1978 in oroer to obtain ultraviolet spectra of astronomical sources. The Observatory has now surpassed its nominal design lifetime of three years in orbit. It carries a 45-cm Ritchie Chretien telescope which feeds two echelle spectrographs with integrating television cameras. Spectra can be obtained in the range from 1150A to 3200A, using either a high dispersion mode with a spectral resolving power of about 104 or a low dispersion mule with a resolution of about 7A. The satellite is in geosynchronous orbit, which has both operational and scientific advantages over low-orbit observatories. Although the problems of calibrating and monitoring the performance of the instrument in orbit have been substantial, its optical and photometric characteristics have proven to be remarkably stable. It should prove to be a useful astronomical facility for some time to come.

The Extreme Ultraviolet Explorer Mission is described. The purpose of this mission is to search the celestial sphere for astronomical sources of extreme ultraviolet (EUV) radiation (100 - 1000 A). This search will be accomplished with the use of three EUV telescopes, each sensitive to different segments, or colors, within the EUV band. A fourth telescope will perform a higher sensitivity search of a limited sample of the sky in a single EUV band. In six months, the entire sky will be scanned at a sensitivity level comparable to existing surveys in other more traditional astronomical bandpasses.

The instrument design is complete and many components and subsystems have been manufactured and tested. Solar-blind, multichannel, pulse counting detectors for two ultraviolet spectral bands have been developed and satisfactory flight units have been chosen. A large, lightweight graphite-epoxy optical bench, utilizing fingerplate joints with no metallic parts in order to minimize thermal expansion, has been built. Tests of the engineering model torque-motor-driven grating carrousel in that this critical system exceeds our tight specifications for accurate and repeatable angular positioning. A complement of large, high-frequency gratings and an echelle is being completed in several laboratories. Software resident in a computer on the spacecraft will control the spectrograph with the capability to alter procedures in response to real-time evaluation of the data.

In order to develop a data base for potential optical degradation of space vacuum ultra-violet instruments, the collected volatile condensed material (CVCM) transmittance was measured in the wavelength region from 115 nm to 300 nm. The parent outgassing materials included: the adhesives, Ablebond 36-2, Trabond BB-211C, EA-9309, and Scotchweld 2216; the paints, Chemglaze Z-306, Z-306 over 9922 primer, Z-306 over AP-131 primer, Cat-A-Lac 463-3-8, 463-3-8 over primer, 3M Nextel 401-C10, and 401-C10 over 901-P1 primer; the resins, Fiberite 934, Solithane 113/C113-300 Formulation #1, and 113/C113-300 Formulation #8; the lubricants, Lube-Lok 4306 and RT/Duroid 5813; and the double-sided adhesive tape 3M-415. The effect of thermal vacuum conditioning of selected materials was also studied. The transmittance measurements were used to calculate the absorption coefficient for each of 28 different source materials versus wavelength.

The various types of UV effects on the skin are classified according to the part of the spectrum and their beneficial or deleterious nature. Some hazardous ultraviolet sources used in industrial processes are described, and examples of photoallergy, phototoxicity, and photosensitization resulting from UV exposures are given. The incidence of skin cancer as a function of geographical location and exposure to sunlight is discussed in relation to natural and artificial exposures to long and short wavelength UV, especially in connection with tanning booths. The conclusion is reached that there is enough ultraviolet in a normal environment to propose a hazard, and additional ultraviolet exposure from industrial or consumer sources is not necessary, and should be eliminated wherever possible.

Observations of naturally-occurring ultraviolet radiation provide us a wealth of knowledge about the nature and mechanisms of the terrestrial atmosphere, ionosphere, and geocorona and the local interstellar medium. The ultraviolet spectrum is so valuable because it corresponds to the energies of atomic and molecular processes such as fundamental resonance transitions, ionization, and dissociation; however, these same properties make ultraviolet technology difficult. Far and extreme ultraviolet observations from rockets and satellites produce accurate synoptic views of the earth's hydrogen and helium atmospheres and their variations. Similarly, the plasmasphere, confined by the earth's magnetic field, is mapped on a global scale by the resonance radiation of the helium ions. Near the magnetic equator, ultraviolet emissions depict the unique behavior of oxygen ions and the precipitation of alpha particles. With the discovery of extended extraterrestrial ultraviolet resonance radiation from hydrogen and helium it was realized that the local interstellar medium (LISM) flows into and interacts with the solar system. The UV radiation patterns accurately define the LISM characteristics.