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The spectrum of autoionizing states of xenon in the vacuum ultraviolet (VUV) was first observed by Beutler using a helium discharge lamp as the light source and a two-meter grating monochromator.
The interactions of VUV radiation with solids are explored in reviews and reports of recent theoretical and experimental investigations from the fields of atomic and molecular physics, solid-state physics, and VUV instrumentation. Topics examined include photoabsorption and photoionization, multiphoton processes, plasma physics, VUV lasers, time-resolved spectroscopy, synchrotron radiation centers, solid-state spectroscopy, and dynamical processes involving localized levels. Consideration is given to the fundamental principles of photoemission, spin-polarized photoemission, inverse photoemission, semiconductors, organic materials, and adsorbates.
Giant pulse Q switched lasers generated plasmas, noting VUV spectral line shifts, asymmetries and existence of satellite lines
The results of experiments performed to check the possibility of stimulated emission in the extreme vacuum ultraviolet (VUV) by an Al(+3) laser-generated plasma are reported. It is concluded that the spectral line intensity anomalies previously observed are not due to population inversion.
The spectrum of Al VII is re-examined in the vuv. A laser-produced plasma is used as a light source. Twenty-four newly classified lines are reported. No new energy levels have been determined.
Three classes of molecular electronic transition lasers produced by hybrid pumping of high pressure rate gas mixtures are discussed. These are (1) rare gas dimer lasers (such as excited Ar2, Kr2, and Xe2) lasing in the VUV, (2) rare gas halide lasers or excimer lasers (such as KrF, ArF, and XeCl excimers) lasing in the UV, and (3) the charge transfer molecular ion laser (such as N2/+/) lasing in the visible range. Laser excitation methods and kinetic sequences are examined for these lasers.
Radiative lifetimes of the eight lowest even parity levels in the doublet system of B I are measured using time-resolved laser-induced fluorescence in the UV and VUV on an atomic beam of boron. The accurate lifetimes provide a base for improved determination of absolute transition probabilities in B I. The techniques described are broadly applicable to measurement of lifetimes of levels with transitions in the visible, UV, and VUV in almost any element.
We are currently developing an atomic oxygen diagnostic to study the degree of oxygen dissociation in ground-based facilities. The absorption of the (sub 3)P - (sup 3)S(sup 0) resonance triplet in the vacuum ultraviolet is a direct measure of the ground state number density of atomic oxygen. Although the integrated line strength is well known for these transitions, the line profile is not. We report the results of a series of experiments in which the line profile is measured in shock-heated oxygen. An ArF excimer laser and a hydrogen Raman shifter generate tunable VUV radiation at the resonance wavelength. The test gas is dissociated oxygen, generated in the Electric Arc Shock Tube (EAST) Facility at NASA-Ames Research Center. By measuring the absorption of known concentrations of atomic oxygen, we are able to study the absorption line profile. The results will serve as a calibration to apply this diagnostic in other flowfields.
Analytical and experimental studies of the rapid transfer of stored populations from metastable states to selected target states of a different species are reported. Both laser-induced or laser-switched collision and laser-induced two-photon spontaneous emission are described. It is shown that the laser-induced collision method is particularly useful in the visible and UV spectral regions. It has applications in photochemistry, gas-phase kinetics, and in high-power, high-energy gas-phase lasers. The anti-Stokes source is useful in the VUV and soft X-ray spectral regions.
Aims: A tunable, high spectral resolution, high effective finesse, vacuum ultraviolet (VUV) Fabry-Perot interferometer (PPI) is designed for obtaining narrow-passband images, magnetograms, and Dopplergrams of the transition region emission line of CIV (155 nm). Methods: The integral part of the CIV narrow passband filter package (with a 2-10 pm FWHM) consists of a multiple etalon system composed of a tunable interferometer that provides high-spectral resolution and a static low-spectral resolution interferometer that allows a large effective free spectral range. The prefilter for the interferometers is provided by a set of four mirrors with dielectric high-reflective coatings. A tunable interferometer, a VUV piezoelectric-control etalon, has undergone testing using the surrogate F2 eximer laser line at 157 nm for the CIV line. We present the results of the tests with a description of the overall concept for a complete narrow-band CIV spectral filter. The static interferometer of the filter is envisioned as being hudt using a set of fixed MgF2 plates. The four-mirror prefilter is designed to have dielectric multilayer n-stacks employing the design concept used in the Ultraviolet Imager of NASA's Polar Spacecraft. A dual etalon system allows the effective free spectral range to be commensurate with the prefilter profile. With an additional etalon, a triple etalon system would allow a spectrographic resolution of 2 pm. The basic strategy has been to combine the expertise of spaceflight etalon manufacturing with VUV coating technology to build a VUV FPI which combines the best attributes of imagers and spectrographs into a single compact instrument. Results. Spectro-polarimetry observations of the transition region CIV emission can be performed to increase the understanding of the magnetic forces, mass motion, evolution, and energy release within the solar atmosphere at the base of the corona where most of the magnetic field is approximately force-free. The 2D imaging of the full vector magnetic field at the height of maximum magnetic influence (minimum plasma beta) can be accomplished, albeit difficult, by measuring the Zeeman splitting of the CIV resonance pair. Designs of multiple VUV FPIs can be developed for integration into future orbiting solar observatories to obtain rapid cadence, spectral imaging of the transition region.
Helium in the superfluid state emits copious amounts of radiation in the ultraviolet region when excited by an electron stream. Conventional laser action using mirrors is impossible in superfluid helium because there are no mirrors that will reflect VUV radiation. By utilizing the distributed feedback method, the superfluid helium can be made to lase. By setting up a standing wave in superfluid helium that has a wavelength equal to, or harmonically related to, half the wavelength of the photon radiation chosen to be emitted as laser radiation by the superfluid helium, the need for end mirrors to produce reflection of the laser radiation is eliminated and reflection occurs instead at the wavefronts of the standing wave. The photons leave the superfluid helium at right angles to the standing wave as coherent radiation having a very high intensity. The standing wave established in the superfluid helium may be an acoustical standing wave, a thermal standing wave (second sound), or an electric standing wave.
The vacuum ultraviolet region allows remote sensing of the upper levels of the solar atmosphere where the magnetic field dominates the physics. Obtaining an imaging interferometer that observes the transition region is the goal of this program. This paper gives a summary of our instrument development program (1998-2005) for a high-spectral-resolution, piezoelectric tunable Vacuum Ultraviolet Fabry-Perot Interferometer (VUV FPI) for obtaining narrow-passband images, magnetograms, and Dopplergrams of the transition region emission line of CN (155nm). A VUV interferometer will allow us to observe the magnetic field, flows, and heating events in the mid-transition region. The MSFC VUV FPI has measured values of FWHM approx. 9pm, FSR approx. 62pm, finesse approx. 5.3 and transmittance approx. 50% at 157nm. For the measurements, the University of Toronto's F2 eximer laser was used as an appropriate proxy for CIV 155nm. This has provided the first tunable interferometer with a FWHM compatible to VUV filter magnetograph.
The technique of rare-gas photoionization has been extended by use of direct laser ionization to electron energies epsilon in the range 0-100 meV, with a resolution Delta(epsilon) of 0.4-0.5 meV (FWHM). Tunable UV light at (Lambda)276 nm is produced using a pulsed Nd:YAG laser and nonlinear mixing techniques. The beam is frequency tripled in a pulsed jet of xenon. The VUV radiation, tunable at (Lambda)92 nm, is then used to photoionize Xe at its 2P(sub 1/2) threshold (single-photon ionization). The photoelectrons produced interact with admixed target gas to generate negative ions through the s-wave capture process. Recent results in electron attachment to SF(sub 6) will be reported which show resonance structure at the opening of the ground-state vibrational channels. This structure corresponds to the process of vibrational excitation + attachment, which is superimposed on the underlying s-wave (direct) capture process. It should be a general phenomenon, present in a wide variety of zero-energy electron attaching molecules.
A versatile tunable VUV photofragment monochromator is described. The instrument uses a unique flashlamp and a single slit monochromator to produce the photofragments. A tunable dye laser is used to detect these fragments via laser induced fluorescence. The results of preliminary design parameter measurements are presented along with the first photofragment spectra obtained with this instrument. It is shown that the SNR is adequate to assign single quantum state photofragment distributions.
Incident shock waves in pure CO have been characterized in the Electric Arc ShockTube facility at NASA Ames Research Center. Spectrally and spatially resolved emissionspectra characterize radiative signatures from CO in the VUV and mid-infrared and atomiccarbon and C2 in the visible. CO absorption of a single vibrational line is also measuredwith a tunable diode laser. The experimental data analyzed here are at a pressure of 0.25Torr in the driven section and span a shock velocity range from 3.4-9.5 km/s. The emissionand absorption signals are analyzed to extract temperature relaxation behind the shockwhich is used to derive the rate of CO dissociation. The emission spectra are compared toresults using different kinetic parameters for CO dissociation and C2 dissociation andexchange. Different rates from the literature are found to match the data from 3.4-6.6 km/sand 6.6-9.5 km/s. Areas for improvement in CO and C2 radiation modeling are suggested onthe basis of the analysis.
Incident shock waves in pure CO have been characterized in the Electric Arc Shock Tube facility at NASA Ames Research Center. Spectrally and spatially resolved emission spectra characterize radiative signatures from CO in the VUV (Vacuum Ultra-Violet) and mid-infrared and atomic carbon and C2 in the visible. CO absorption of a single vibrational line is also measured with a tunable diode laser. The experimental data analyzed here are at a pressure of 0.25 Torr in the driven section and span a shock velocity range from 3.4-9.5 km/s. The emission and absorption signals are analyzed to extract temperature relaxation behind the shock which is used to derive the rate of CO dissociation. The emission spectra are compared to results using different kinetic parameters for CO dissociation and C2 dissociation and exchange. Different rates from the literature are found to match the data from 3.4-6.6 km/s and 6.6-9.5 km/s. Areas for improvement in CO and C2 radiation modeling are suggested on the basis of the analysis.
Quantum efficiency measurements are given for coronene and liumogen coatings designed to enhance UV sensitivity for silicon charge coupled device imaging detectors. Coatings on quartz and on UDT PIN 10DP photodiodes were tested. The wavelength range extended from 153.7 to 50.0 nm in the vacuum ultraviolet. Similar measurements were made for coronene, liumogen, and stilbene-3 laser dye films on quartz disks relative to sodium salicylate. Sodium salicylate and coronene are the most efficient waveshifters down to 50 nm so far observed. Coronene's fairly constant quantum efficiency over such a wide wavelength range into the far VUV makes it a useful waveshifter for UV and VUV applications.
The fluorescence properties of UV sensitive organic phosphors and the radiometric properties of phosphor coated silicon detectors in the VUV, UV, and visible wavelengths are described. With evaporated films of coronene and liumogen, effective quantum efficiencies of up to 20% have been achieved on silicon photodiodes in the vacuum UV. With thin films of methylmethacrylate (acrylic), which are doped with organic laser dyes and deposited from solution, detector quantum efficiencies of the order of 15% for wavelengths of 120-165 nm and of 40% for wavelengths above 190 nm have been obtained. The phosphor coatings also act as antireflection coatings and thereby enhance the response of coated devices throughout the visible and near IR.