2π Sr Research Articles

Rate of NO2 photolysis from the surface to 7.6 km altitude in clear‐sky and clouds

The photolysis of NO2 by solar UV radiation produces ozone in the troposphere. Radiative transfer models predict an increase in actinic UV flux with altitude, but this has never been well documented experimentally. This paper presents direct airborne measurements of both upwelling and downwelling flux (2π sr each) from 0.2 to 7.6 km for clear‐sky conditions and 58° solar zenith angle. The downwelling flux increases by 33% and upwelling flux increases by a factor of four going from the surface to 7.6 km. Excellent agreement was found with models using detailed solutions to the radiative transfer equation or the six‐stream approximation, while a number of two‐stream computer models agreed within 10 to 25%. Compared to clear‐sky measurements, in‐cloud enhancement of up to 58% was also observed.

In situ calibration technique for UV spectral radiometers

A technique for calibrating spectral radiometers measuring global (2π sr) irradiance using solar irradiance at the top of the atmosphere as the absolute irradiance reference is reported. In addition to providing a calibration at all measured wavelengths, the technique provides a direct measure of the angular response of the radiometer. For instruments that can be used to measure the ultraviolet-B region, the calibration also provides an estimate of the ozone column amount.

X-ray damage to optical components using a laser-plasma source

X-ray damage to optical surfaces consisting of melting, fracturing, cracking, and cratering is produced, and then analyzed using interference contrast microscopy and stylus profilometery. The test samples are irradiated by 0.5–1.6 keV x rays at fluence levels up to 5.5 cal/cm2. The x rays originate from L-shell transitions in copper ions, produced when 1.25-μm-thick targets are irradiated at 1.3 kJ energy by a 1.054 μm wavelength laser. The x-ray emission is found to be nearly isotropic over 2π sr, while the plasma mass-flow distribution is peaked along the laser axis. Hence, contamination of the test sample by target debris or plasma is greatly reduced by placing the samples off axis from the laser beam, in addition to the use of beryllium shields.

KeV x-ray production using 50 mJ KrF laser produced plasmas at 1 and 100 ps

The emission of 800–1400 eV x rays from plasmas produced by KrF discharge laser pulses with durations in the range of 1 and 100 ps with energies up to 50 mJ has been studied using various metal targets. The emission spectra, angular distribution, and x-ray conversion efficiencies into 2π Sr have been measured in vacuum. Peak conversion efficiencies of 10%–13% were obtained for Fe, Co, Ni, Cu, and Zn when a 90 ps, 50 mJ pulse was used. A 2 ps, 40 mJ pulse yielded efficiencies of 8%–10% with plasma reflectivity accounting for the reduction in conversion efficiency. An 850 fs, 35 mJ pulse gave reduced yields of 4% for Cu. In a background gas of 1 atm helium a reduction of conversion efficiency by 15% was observed for 90 ps pulses.

Latitudinal variation of measured O3 photolysis frequencies J(O1D) and primary OH production rates over the Atlantic Ocean between 50� N and 30� S

The latitudinal variation of the photolysis frequency of ozone to O(1D) atoms, J(O1D), was measured using a filter radiometer during the cruise ANT VII/1 of the research vessel Polarstern in September/October 1988. The J(O1D) noon values exhibited a maximum of 3.6×10-5 s-1 (2π sr) at the equator and decreased strongly towards higher latitudes. J(O1D) reached highest values for clean marine background air with low aerosol load and almost cloudless sky. The J(O1D) data, measured under these conditions and a temperature of 295 K, can be expressed by: % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOsaiaacI% cacaqGpbWaaWbaaSqabeaaiiaacqWF8baFaaGccaqGebGaaeykaiaa% bccacqWF9aqpcaqGGaGaaeyzaiaabIhacaqGWbGaaeiiaiaabUhacq% GHsislcaaI4aGaaiOlaiaaicdacaaIYaGaeyOeI0IaaGioaiaac6ca% caaI4aGaaiiEaiaaigdacaaIWaWaaWbaaSqabeaacqGHsislcaaIZa% aaaOGaaeiiaiaabIhacaqGGaGaam4uaiabgUcaRiaaiodacaGGUaGa% aGinaiaacIhacaaIXaGaaGimamaaCaaaleqabaGaeyOeI0IaaGOnaa% aakiaadofadaahaaWcbeqaaiaaikdaaaGccaGG9bGaaeikaiaaboha% daahaaWcbeqaaiabgkHiTiaaigdaaaGccaGGPaaaaa!5EE9!\[J({\text{O}}^| {\text{D) }} = {\text{ exp \{ }} - 8.02 - 8.8x10^{ - 3} {\text{ x }}S + 3.4x10^{ - 6} S^2 \} {\text{(s}}^{ - 1} )\] where S represents the product of the overhead ozone column (DU) and the secant of the solar zenith angle. The meridional profile of the primary OH radical production rate P(OH) was calculated from the J(O1D) measurements and simultaneously recorded O3 and H2O mixing ratios. While the latitudinal distribution of J(O1D) and water vapour was nearly symmetric to the equator, high tropospheric ozone levels up to 40 ppb were observed in the Southern Hemisphere, SH, resulting in higher P(OH) in the SH.

Latitudinal variation of measured NO2 photolysis frequencies over the Atlantic Ocean between 50� N and 30� S

Using a filter radiometer, the meridional profile of the NO2 photolysis frequency, J(NO2), was measured between 50° N and 30° S during the cruise ANTVII/1 September/October 1988 of the research vessel Polarstern on the Atlantic Ocean. Simultaneously, global broadband irradiance and acrosol were monitored. Clean marine background air with low aerosol loads (bsp=(1–2)×10-5 m-1) was encountered at the latitudes 25° N–30° N and 18° S–27° S, respectively. Under these conditions and an almost cloudless sky J(NO2) reached 7.3×10-3 s-1 (2π sr) for a zenith angle of 30°. Between 30° N and 30° S, the latitudinal variation of the J(NO2) noontime maxima was less than ± 10%, while the mean value at noon was 7.8×10-3 s-1. For the set of all data between 50° N and 30° S, a nearly linear correlation of J(NO2) vs. global broadland irradiance was found. The slope of (8.24±0.03)×10-5 s-1/mW cm-2 agrees within 10% with observations in Julich (51° N, 6.2° E).

Performance optimization of a high-repetition-rate KrF laser plasma x-ray source for microlithography

In order to develop a high-intensity laser plasma x-ray source appropriate for industrial application of x-ray lithography, experiments have been carried out using a high-repetition-rate (up to 40 Hz) excimer laser (249 nm, 300 mJ) with a power density of 2 × 10 13 W/ cm 2 in the laser focus. In this study emphasis is given to remedying specific problems inherent in operating the laser plasma x-ray source at high repetition rates and in its prolonged operation. Two different methods of minimizing the production of target debris are investigated. First, the use of helium as a quenching gas results in a reduction of the amount of atomic debris particles by more than two orders of magnitude with negligible x-ray absorption. Second, a tape target as opposed to a solid target reduces the production of larger debris particles by a further factor of 100. Remaining debris is stopped by an aluminized plastic or beryllium filter used to avoid exposure of the resist by plasma ultraviolet radiation. The x-ray source has been used to image x-ray transmission mask structures down to 0.3 μm onto general purpose x-ray photo-resist. Results have been analyzed with SEM. The x-ray emission spectrum of the repetitive laser plasmas created from an iron target has been recorded and the conversion efficiency of the laser light into x-rays that contribute to exposure of the resist was measured to be 0.3% over 2π sr.

Plasma soft x-ray source generated by 4-ns excimer laser pulses

A XeCl excimer laser system is described which generates short-duration (4 ns) pulses of up to 980 mJ in energy. Pulses of 800 mJ have been focused to an intensity of ∼2×1012 W cm−2 on an iron target to produce soft x rays. Measurements of x rays in the 0.8–1.4-keV range have demonstrated 44 mJ energy per pulse into 2π sr, and a pulse width of 5.3 ns (FWHM). The estimated laser to x-ray energy conversion efficiency was ∼5.5%.

X-ray absorption spectroscopy: A fluorescence detection system based on a plastic scintillator

A fluorescence detection system based on a plastic scintillator is presented that can be used for both X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine-structure (EXAFS) spectroscopy. Its counting rate is limited by the pulsation frequency of the synchrotron radiation (3.16×10 6 counts s −1), and can be theoretically extended to roughly 5×10 7 counts s −1 if used on a multibunch storage ring synchrotron radiation source. Its physical characteristics (fluorescence decay time and fast electronics) are such that the dead-time correction is entirely defined by the revolution period of the charged particles in the storage ring. It shows a broad spectral response and is particularly well adapted to the measurement of hard X-rays (from 6 to 25 keV). Its volume is small (diameter 60 mm; height 240 mm), and filters of small dimensions are used to preferentially remove the scattered radiation. The entrance window of the detector is placed at 2–3 mm above the top of the sample, and a solid angle of collection of nearly 50% of 2π sr is achieved. The shape of the plastic scintillator can be easily modified to fit various geometries. It operates in both horizontal and vertical planes. It is about ten times less expensive than an energy-dispersive detection system based on a single Ge solid-state detector. The detector presents a high sensitivity. It is possible to obtain the entire EXAFS spectrum of an electrochemically (under potential deposition) deposited monolayer of Cu atoms on gold, with acquisition time of less than one hour (compared to 25 h for a Ge solid-state detector). Orientation-dependent X-ray absorption spectroscopy was performed on thin (800 Å) copper phthalocyanine film, and the spectra of diluted Cu 2+ ions in aqueous solution (18 ppm) and Co atoms in YBa 2Cu 3O 7 powder (230 ppm) were also measured to assess the sensitivity of the detector.

A photoelectric detector for the measurement of photolysis frequencies of ozone and other atmospheric molecules

Photoelectric detectors for the measurement of photolysis frequencies of different trace gases in the atmosphere are described. They exhibit uniform response characteristics over one hemisphere (2π sr) and wavelength characteristics closely matched to those of the photolysis frequencies J O1D, J NO2, and J NO3, respectively. Absolute calibration of the J O1D detector was performed by chemical actinometry with an accuracy of ±16 percent. Simultaneous measurements of J NO2 and J O1D are presented.

Magnetic bottle electron spectrometer using permanent magnets

Design principles and initial results are presented for a magnetic bottle electron spectrometer of high collection efficiency (2π sr) and good energy resolution. The instrument duplicates the carefully shaped axially decreasing magnetic field configuration of Kruit and Read [J. Phys. E 16, 313 (1983)], but replaces the high-field electromagnet central to the Kruit–Read design with two simple pole pieces energized by permanent magnets. The use of permanent magnets requires modifications of the transition region (between the high-field electron production zone and the low-field drift tube analyzer) to avoid axial field reversals associated with fringing fields.

New display-type analyzer for the energy and the angular distribution of charged particles

A new principle for analyzing the kinetic energy as well as the angular distribution of charged particles has been discovered. A new display type analyzer was constructed according to theory. It consists of an inner hemispherical grid and an outer hemispherical electrode which has a radius two times larger than that of the inner grid. Charged particles with the same kinetic energy radiate from one point to all directions inside the inner grid, are repelled by the electric field between the two spheres, and converge at the point which is symmetric to the center of the hemispheres. When an aperture is put at the point, the angular distribution of the charged particles can be observed using a two-dimensional detector which is positioned out of the aperture. The characteristics of the analyzer are (1) the acceptance cone is ultimately wide, for instance, 2π sr for the charged particles emitted from a flat surface, (2) the pattern obtained is not distorted, and (3) the two electrodes are very simple and easy to construct.

新しい二次元表示型球面鏡分析器の解析

A display type spherical mirror analyzer was newly developed and its nature was analyzed in detail. It consists of an inner hemispherical grid, an outer hemispherical electrode whose radius is two times large as that of the inner grid, a small aperture, and two dimensional detector. Only the charged particles with the same kinetic energy can exit through the aperture and the angular distributions of them are observed by the two dimensional detector. The characteristics of the analyzer are (1) the acceptance cone is ultimately wide (2π sr), (2) the pattern obtained is not distorted, and (3) the structure of the components are very simple and easy to construct. The loci of the charged particles, the resolution of the analyzer, and the flight-time of the particles were analytically expressed.

Spectroscopy of L-series transitions for x-ray laser photopumping

Candidate photopumping materials for resonant photoexcitation x-ray laser schemes were examined to determine spectral line position and radiant line intensity. Improved spectroscopic techniques have permitted several comparative measurements to be made with greater sensitivity and resolution than that of earlier work. A cylindrically focused 0.527-μm laser beam was used to generate the plasma source emission by irradiating thin foil targets. Selected wavelength regions in the 10–17-A range were studied for possible line coincidences between K-series transitions in F, Ne, and O with emission from transition-metal targets. Within the measurement accuracy of ±2 mA, exact spectral line coincidences were found for Mn with the F H-β line at 12.643 A and for both Mn and Cr with the F He-β line at 14.458 A. The Mn line at 12.643 has been identified, using ab initio atomic-structure calculations, as the 1D2–1F3 transition in Be-like Mn xxii. This line was found to yield 2–5 mJ into 2π sr with 20 J of laser energy on target. Spectral identifications and wavelengths for Be-like Ti, Cr, Mn, Fe, and Co lines, for Li-like Ti, Cr, and Mn lines, and for N-like Mn lines also resulted from this work.

The effectiveness of radiation as a function of angle of incidence on the surface of specimen

The effectiveness of radiation as a function of angle of incidence on polymer films has been calculated and examined by exposure tests. Theoretical considerations for different coefficients of transmission and different indices of refraction show that the radiation with normal incidence is the most effective. However, it is concluded that a photoreceptor which is cosine corrected for a solid angle of 2π sr does undervalue radiation with oblique incidence. The exposure tests confirm these theoretical results but also show an additional unexplained peak of effectiveness for radiation with angles of incidence of about 20°.

High brightness laser/plasma source for high throughput submicron x-ray lithography

Laser irradiation of solid targets has been demonstrated to produce an extremely intense source of soft x rays. Conversion efficiencies of greater than 10% emission of over 1 keV radiation into 2π sr have been demonstrated with subjoule 1.06 μ laser pulses. This high conversion efficiency is achieved by using subnanosecond pulse lengths, tight focusing, and shaped pulses. A laser capable of producing the requisite high quality laser pulses at 100 Hz repetition rates has been constructed using newly developed slab techniques to maintain good beam quality at high average powers. A windowless target chamber has been designed to mate to x-ray stepper/aligners which are now being built. The present laser will permit average x-ray intensities of 2 mW/cm2 to be realized behind current (boron nitride) x-ray masks with negligible penumbral effects. This is an order of magnitude higher than possible with conventional electron beam impact sources and, with the present or upgraded laser system, should assist the commercialization of x-ray steppers.

Direct measurements of ozone and nitrogen dioxide photolysis rates in the troposphere

Direct measurements of the rate of O3 photolysis to O2(1Δg) and O(1D) and of NO2 photolysis to NO and O(3P) are reported as photolysis frequencies j(O3) and j(NO2). The effects of solar zenith angle, total ozone column, cloud cover, aerosol loading, temperature, pressure, and altitude are examined. For a clear sky, zero albedo, and zenith angle between 0° and 65°, the expression j (NO2) = 1.67 × 10−2 exp (−0.575 sec θ) (s−1) gives NO2 photolysis frequencies (photolysis rates per unit reactant) to within about 10% of the measured values, where θ is the solar zenith angle. Pressure has no measurable effect on j(NO2) between 0.15 and 1.2 bars. Temperature has only a small effect between 230 and 400 K, which can be described in terms of an effective activation energy of 0.48±0.05 kJ mol−1. Frequencies of ozone photolysis to O(1D) depend strongly on overhead ozone column and temperature as well as zenith angle; for 300 K, a clear sky, zero albedo, 45° zenith angle, 0.345‐cm ozone column, and altitude between 1.6 and 6 km, j(O3) = 1.6(±0.25) × 10−5 s−1. From 300 to 273 K, j(O3) drops by 40±3% for a 65° zenith angle and a 0.306‐cm ozone column; this value is not valid for different effective ozone columns. Measured photolysis frequencies show only weak dependence on altitude and aerosol loading. These frequencies were measured with instruments sensitive to radiation from the upward 2π sr only. Clouds dramatically reduce both photolysis frequencies, but they reduce the total radiation by a significantly larger factor. Airborne UV radiometers, calibrated against direct measurements of j(NO2), were used to measure albedos of many surfaces. While natural surfaces such as vegetation and oceans have albedos near zero, dense clouds and snow have an albedo near unity. With increasing altitude, molecular and particulate scattering often increase the effective albedo with respect to photolysis frequencies.

Highly resolved electron spectra for resonantly enhanced four-photon ionization of no

Electron energy spectra of (2 + 2)-photon ionization of NO are reported. The intermediate resonance is A2 + and scans are made over the rotational width of u = 0 and 1. A new type of spectrometer is used accepting 2π sr at a resolution of 15 meV. The vibrational distribution peaks at Δ v = 0 (Franck-Condon for direct ionization) but also at the highest energetically allowed Δ v . We present evidence for pre-ionization via a dissociative channel.

Scattering from high efficiency diffraction gratings

This paper has characterized and measured scatter from high efficiency and reflective diffraction gratings. Three major types of scatter are identified: (1) random, which occurs over 27pi sr; (2) band or ghost scatter, which occurs in the plane of incidence; and (3) structured scatter, which is a symmetrical pattern repeated about each order. Measurements were taken at 10.6 Am on gratings made by ruling, ion etching, holography, or a combination of these techniques. We found that the characteristic scatter from these high efficiency gratings depends strongly on the way the gratings are fabricated.

The determination of the energies and angles of emission of fission fragments from a 252Cf source using a xenon proportional scintillation detector

The response of a parallel plate xenon proportional scintillation detector to fission fragments from a 252Cf source, mounted on the cathode in the scintillation cell, is described. The energies of the fragments were determined from the amplitudes of the pulses; the pulse height spectra for fragments accepted over a solid angle of 2π sr are found to be similar to those from a semiconductor detector. By analysing the profiles of the pulses the angles of emission of the fragments relative to the axis of the detector were determined, and the energy spectra of fragments emitted within various angular ranges between 0 and π 2 are presented. In addition to the binary fission data, the energy spectra of fragments detected in coincidence with α-particles released in the ternary fission of 252Cf are shown for various angles of emission of the α-particle relative to the fragment direction.