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Showing papers on "Wavelength published in 1987"


Journal ArticleDOI
TL;DR: An experiment to probe the (quasi)localization of the photon is proposed, in which optical layers are constructed following the Fibonacci sequence, which has scaling with respect to the number of layers, as well as an interesting fluctuation.
Abstract: An experiment to probe the (quasi)localization of the photon is proposed, in which optical layers are constructed following the Fibonacci sequence. The transmission coefficient has a rich structure as a function of the wavelength of light and, in fact, is multifractal. For particular wavelengths for which the resonance condition is satisfied, the light propagation has scaling with respect to the number of layers, as well as an interesting fluctuation.

468 citations


Journal ArticleDOI
TL;DR: In this article, it was demonstrated that observed saturation spectra are not solely due to individually saturated waves but most likely result from amplitude limiting instabilities arising from wave superposition, and that, while the spectrum is saturated at large wavenumbers, the total kinetic energy per unit mass and the characteristic vertical wavelength increase with altitude.
Abstract: The slope and power spectral density of atmospheric velocity fluctuations versus vertical wavenumber at large wavenumbers are observed to be nearly independent of altitude. It is suggested that such a universality is due to saturation of short vertical-scale fluctuations. A brief review of linear gravity wave saturation theory indicates a physical basis for such spectra. It is demonstrated that observed saturation spectra are not solely due to individually saturated waves but most likely result from amplitude limiting instabilities arising from wave superposition. It is also shown that, while the spectrum is saturated at large wavenumbers, the total kinetic energy per unit mass and the characteristic vertical wavelength increase with altitude. Both of these predictions are consistent with observations.

463 citations


Journal ArticleDOI
TL;DR: In this paper, the phase mismatch in the four-wave mixing process is clarified experimentally in a single-mode fiber transmission line at 825 nm wavelength, and the generated power of approximately 20 pW is measured successfully for input signal powers below 1 mW by the technique utilizing a heterodyne receiver and lock-in detector.
Abstract: The generation wave efficiency with respect to phase mismatch in the four-wave mixing process is clarified experimentally in a single-mode fiber transmission line at 825 nm wavelength. The generated power of approximately 20 pW is measured successfully for input signal powers below 1 mW by the technique utilizing a heterodyne receiver and lock-in detector. The calculated efficiency as a function of the equivalent frequency separation can well explain and reflect the results obtained experimentally. Furthermore, the efficiency at zero chromatic dispersion wavelengths of 1.3 and 1.55 μm is also discussed considering chromatic dispersion slope against wavelength.

393 citations


PatentDOI
TL;DR: A vibration wave device having a resilient member and electro-mechanical energy conversion means for inducing a travelling vibration wave in the resilient member, the traveling vibration wave being used as a drive source, includes means provided on at least one member of the vibrational wave device at a location integer times or approximately integer times 1/2 of the wavelength of a vibration wave which may produce noise and making the dynamic rigidity of the member non-uniform.
Abstract: A vibration wave device having a resilient member, and electro-mechanical energy conversion means for inducing a travelling vibration wave in the resilient member, the travelling vibration wave being used as a drive source, includes means provided on at least one member of the vibration wave device at a location integer times or approximately integer times 1/2 of the wavelength of a vibration wave which may produce noise and making the dynamic rigidity of the member non-uniform.

360 citations


Journal ArticleDOI
TL;DR: Two-wavelength phase-shifting interferometry is applied to an interference phase-measuring microscope enabling the measurement of step features and a measurement dynamic range of 10(4) is obtainable.
Abstract: Two-wavelength phase-shifting interferometry is applied to an interference phase-measuring microscope enabling the measurement of step features. The surface is effectively tested at a synthesized equivalent wavelength lambda(eq) = lambda(a)lambda(b)/| lambda(a) - lambda(b)| by subtracting phase measurements made at visible wavelengths lambda(a) and lambda(b). The rms repeatability of the technique is lambda/1000 at the equivalent wavelength. To improve the precision of the data, the phase ambiguities in the single-wavelength data are removed using the equivalent wavelength results to determine fringe orders. When this correction is made, a measurement dynamic range (feature height/rms repeatability) of 10(4) is obtainable. Results using this technique are shown for the measurement of an optical waveguide and a deeply modulated grating.

294 citations


Journal ArticleDOI
TL;DR: In this paper, the compositional dependence of the ultrasonic velocity and absorption of 32 silicate melts has been determined as a function of temperature (1175-1925 K) and frequency (3-12 MHz).
Abstract: The ultrasonic velocity and absorption of 32 silicate melts have been determined as a function of temperature (1175–1925 K) and frequency (3–12 MHz). The samples include the components SiO2, TiO2, Al2O3, FeO, MgO, CaO, SrO, BaO, Li2O, Na2O, K2O, Rb2O, and Cs2O, and range from simple alkali silicates to multicomponent synthetic and natural melts. The relaxed sound speed varies systematically with substitution of the alkali and alkaline earth oxides, decreasing monotonically with increased cation radius. An algorithm for the compositional dependence of the ultrasonic velocity at 1673 K:1/c=∑ (xi,υ/c¯i), where xi,υ is the volume fraction of component i and c¯i is independent of composition, is capable of predicting relaxed melt velocities to within 4%. The temperature dependence of the sound speeds in the nondispersive region is quite small, ≈1 part in 104 K−1. A simple linear model for the compositional dependence of the derived property (δV/δP)T has an uncertainty of 13%, approximately equal to that expected from the propagation of errors involving sound speed, density, thermal expansion, and heat capacity. The contributions of the changes in sound speed and density with temperature are nearly the same in their influence on the temperature dependence of the bulk modulus of natural melts. The relaxation properties c/c0 (ratio of the sound speed to the low-frequency value) and αλ (absorption per wavelength) of all of the liquids studied are very similar when plotted against ωτ, the product of the angular frequency and the shear relaxation time. Both properties are consistent with τ equal to 1% of the product of the low-frequency shear viscosity and bulk modulus. Dispersion begins when ωτ ≃ 0.1 and the limiting high-frequency sound speed c∞ is about 2.3 times c0. The product αλ attains a maximum value of about 1.4 when ωτ ≃ 0.8. The data cannot be explained by a single relaxation time in the melts; rather, a spectrum of relaxation times is indicated.

266 citations


Journal ArticleDOI
TL;DR: In this article, the authors examined 13 cases of mesoscale wave disturbances and their environment to isolate common features for these cases and to determine possible energy sources for the waves, which is consistent with the hypothesis that the energy source needed to initiate and sustain the wave disturbances may be related to a geostrophic adjustment process associated with upper-tropospheric jet streaks.
Abstract: Published data on 13 cases of mesoscale wave disturbances and their environment were examined to isolate common features for these cases and to determine possible energy sources for the waves. These events are characterized by either a singular wave of depression or wave packets with periods of 1-4 h, horizontal wavelengths of 50-500 km, and surface-pressure perturbation amplitudes of 0.2-7.0 mb. These wave events are shown to be associated with a distinct synoptic pattern (including the existence of a strong inversion in the lower troposphere and the propagation of a jet streak toward a ridge axis in the upper troposphere) while displaying little correlation with the presence of convective storm cells. The observed development of the waves is consistent with the hypothesis that the energy source needed to initiate and sustain the wave disturbances may be related to a geostrophic adjustment process associated with upper-tropospheric jet streaks.

265 citations


Journal ArticleDOI
TL;DR: In this paper, the absorption cross-sections of NO 2 have been measured in the wavelength range 200 - 700 nm at 298 K with a spectral resolution of 0.04 nm, and averaged over 1 nm intervals and over the atmospheric wavelength intervals used in solar photolysis calculations.
Abstract: The absorption cross-sections of NO 2 have been measured in the wavelength range 200 – 700 nm at 298 K with a spectral resolution of 0.04 nm. The data were acquired digitally, allowing post-processing such as integration in different wavelength intervals. The cross-sections are averaged over 1 nm intervals and over the atmospheric wavelength intervals used in solar photolysis calculations.

247 citations


Journal ArticleDOI
TL;DR: It is argued that the wavelength dependence of quantum yield reflects the distribution of quanta between the two photosystems with the quantum yield dropping at wavelengths strongly absorbed by chlorophyll b as this is mainly associated with photosystem II.
Abstract: The wavelength dependence of photosynthetic quantum yield was measured in a leaf disc oxygen electrode using narrow-band interference filters. Photorespiration was suppressed by measuring oxygen evolution in air containing ~ 1% CO2. Rates of oxygen evolution were determined as a function of absorbed irradiances between 0 and 100 µmol quanta m-2 s-1 and the slope was taken as the quantum yield. The wavelength-dependence previously observed in many species was confirmed for pea and spinach leaves. The maximum quantum yields obtained here and by others are close to 0.111 mol O2 mol-1 quanta for red light. Given the wavelength dependence of quantum yield and the spectral distribution of light, the quantum yields for various white lights were calculated to be around 85% of the red maximum. The quantum yields in white light were the same for plants grown at different irradiances. It is argued that the wavelength dependence of quantum yield reflects the distribution of quanta between the two photosystems with the quantum yield dropping at wavelengths strongly absorbed by chlorophyll b as this is mainly associated with photosystem II.

237 citations


Journal ArticleDOI
TL;DR: In this article, a series of observations designed to probe the nature of sunspots by detecting their influence on high-degree p-mode oscillations in the surrounding photosphere is presented.
Abstract: The paper presents the initial results of a series of observations designed to probe the nature of sunspots by detecting their influence on high-degree p-mode oscillations in the surrounding photosphere. The analysis decomposes the observed oscillations into radially propagating waves described by Hankel functions in a cylindrical coordinate system centered on the sunspot. From measurements of the differences in power between waves traveling outward and inward, it is demonstrated that sunspots appear to absorb as much as 50 percent of the incoming acoustic waves. It is found that for all three sunspots observed, the amount of absorption increases linearly with horizontal wavenumber. The effect is present in p-mode oscillations with wavelengths both significantly larger and smaller than the diameter of the sunspot umbrae. Actual absorption of acoustic energy of the magnitude observed may produce measurable decreases in the power and lifetimes of high-degree p-mode oscillations during periods of high solar activity.

224 citations


Journal ArticleDOI
TL;DR: In this article, the authors studied analytically normal modes trapped in a liquid-filled layer sandwiched between two solid half-space, and found that a slow wave, similar to the tube wave found by Blot, exists for all wavelengths.
Abstract: The dynamics and seismic radiation of fluid-filled cracks have been studied by numerous authors, as models for tremor and for long-period events observed at volcanoes. One of the most intriguing results of the recent models is the existence of a very slow wave propagating along the crack boundary. In order to bet- ter understand this slow wave, which has so far only been studied numerically, we studied analytically normal modes trapped in a liq- uid layer sandwiched between two solid half--space,;. A slow wave, similar to the tube wave found by Blot, exists for all wavelengths. In the short wavelength limit, this wave approaches the Stoneley wave for the liquid-solid interface. Unlike the tube w; re, however, as the wavelength increases to infinity, both the phase and group velocities approach zero, in inverse proportion to the square root of wavelength. The phase velocity and amplitude of this slow wave are in good agreement with those obtained by the numerical stud- ies on the dynamics of fluid-filled cracks by two-dimensional and three-dimensional finite difference methods. In the past the size of a magma body has been estimated from volcanic tremor periods and the acoustic velocity in the fluid. These estimates should be drasti- cally reduced if the slow wave donfinates (he tremor. For exan?ple, the extremely long-period volcanic tremor, with periods up to "s, observed at Mount Aso may be generated by a fluid-filled crack of modest size, a magma body 0.5 m thick end 0.5 km long.

Journal ArticleDOI
TL;DR: In this paper, a theoretical basis has been provided for the application of LDS to size-measurement in suspensions and emulsions, and for extension of this method to the lower size ranges and those cases in which the refractive indices of the disperse and continuous phases are similar.
Abstract: Laser diffraction spectrometry (LDS) is often claimed to operate on the principle of Fraunhofer diffraction. This is only true, however, if particles are large compared to the wavelength of light or if the ratio of the refractive indices of the disperse and continuous phases, m, is clearly different from unity. In this study it has been established that LDS, as applied to particle and droplet sizing in suspensions and emulsions, is based on Miescattering. Scattering patterns of single particles may be calculated if the refractive indices of both phases are known. Thus, a theoretical basis has been provided for the application of LDS to size-measurement in suspensions and emulsions, and for extension of this method to the lower size ranges and those cases in which the refractive indices of the disperse and continuous phases are similar. Extension of the work presented in this paper will enable the calculation of scattering matrices so that calibration of the apparatus with standard materials may be avoided.

Journal ArticleDOI
Ann Roberts1
TL;DR: In this paper, a rigorous electromagnetic theory of the diffraction of radiation by a circular aperture in a thick screen is developed, and the effects of varying the thickness of the screen and varying the wavelength, polarization, and angle of incidence of the incident wave on the reflection and transmission properties of a screen are investigated.
Abstract: A rigorous electromagnetic theory of the diffraction of radiation by a circular aperture in a thick screen is developed. In particular, the case of an incident plane wave is considered, and the effects of varying the thickness of the screen and of varying the wavelength, polarization, and angle of incidence of the incident wave on the reflection and transmission properties of the screen are investigated.

Book ChapterDOI
01 Jan 1987
TL;DR: In this article, the influence of diffracted waves on tomographic observations is discussed and the authors conclude that strong diffraction effects are expected when the scale of heterogeneity is in the order of the seismic wavelength, but the smallest detail one wants to resolve with seismic tomography is typically one or two orders of magnitude larger.
Abstract: This chapter deals with the influence of diffracted waves on tomographic observations. Probably most workers in tomography are aware of the existence of such waves and of their potential to interfere with the direct wave on which the tomographic interpretation is based. Strong diffraction effects are expected when the scale of heterogeneity is in the order of the seismic wavelength, but the smallest detail one wants to resolve with seismic tomography is typically one or two orders of magnitude larger. Can we safely neglect diffraction in this case?

Journal ArticleDOI
TL;DR: In this paper, a third-order sum-and difference-frequency conversion of pulsed-dye-laser radiation is investigated in the rare gas, Kr. The frequency ωR(λR = 216.6 nm) is resonant with the Kr two-photon transition 4p-5p[5/2, 2].
Abstract: Resonant third-order sum- and difference-frequency conversion (ωuv = 2ωR ± ωT) of pulsed-dye-laser radiation is investigated in the rare gas, Kr. The frequency ωR(λR = 216.6 nm) is resonant with the Kr two-photon transition 4p–5p[5/2, 2]. On tuning ωT in the range λT = 219–364 nm, the sum frequency generates light in the extreme ultraviolet (XUV) (λxuv = 72.5–83.5 nm). In agreement with theoretical predictions, the conversion efficiency η is almost constant within this spectral range. At input powers PR = 14 kW and PT = 400 kW, the pulse power of the XUV exceeded Pxuv = 20 W. However, absorptions in the Kr gas reduced the power of the detected XUV light to about 5 W (effective efficiency, η = 1.2 × 10−5). With laser light at λT = 272–737 nm, the difference frequency generates continuously tunable radiation in the vacuum ultraviolet (VUV) (λvuv = 127–180 nm). In this range, the conversion efficiency increases with wavelength by more than 1 order of magnitude. At λvuv = 135 nm, for example, input powers PR = 0.2 MW and PT = 1.2 MW generate VUV light with Pvuv = 250 W (n = 1.8 × 10−4). At λvuv = 175 nm, a lower input (PR = 80 kW, PT = 560 kW) produced VUV light pulses of Pvuv = 1.8 kW (η = 2.8 × 10−3). This spectral variation of η is in agreement with the calculated wavelength dependence of the nonlinear susceptibility and of the gas pressure required for optimum VUV output.

Journal ArticleDOI
TL;DR: In this paper, an analysis of the effectiveness with which active methods can be used for producing global reductions in the amplitude of the pressure fluctuations in a harmonically excited enclosed sound field is presented.

Journal ArticleDOI
TL;DR: Spatial distributions of the near-field and internal electromagnetic intensities have been calculated and experimentally observed for dielectric cylinders and spheres which are large relative to the incident wavelength.
Abstract: Spatial distributions of the near-field and internal electromagnetic intensities have been calculated and experimentally observed for dielectric cylinders and spheres which are large relative to the incident wavelength. Two prominent features of the calculated results are the high intensity peaks which exist in both the internal and near fields of these objects, even for nonresonant conditions, and the well-defined shadow behind the objects. Such intensity distributions were confirmed by using the fluorescence from iodine vapor to image the near-field intensity distribution and the fluorescence from ethanol droplets impregnated with rhodamine 590 to image the internal-intensity distribution.

Journal ArticleDOI
TL;DR: In this paper, a wave velocity field in the surf zone of two California beaches is estimated using a biaxial electromagnetic current meters (BEM) and model testing provides insight into the limits, capabilities and reliability of the estimators.
Abstract: Wavenumber-frequency spectra of the infragravity (periods 20-200 sec) wave velocity field in the surf zone of two California beaches are estimated. Because the longshore arrays of biaxial electromagnetic current meters are relatively short (comparable to the wavelengths of interest), high resolution spectrum estimators are required. Model testing provides insight into the limits, capabilities and reliability of the estimators used in this paper. On all 15 days analyzed, between 42% and 88% of the longshore current variance at the array is contributed by low mode (n≤2) edge waves. (Percentage estimates are not made at a few frequencies because the array is positioned near nodes.) The low mode signal in the cross-shore velocity at the arrays is usually masked by unresolvable high mode and/or leaky waves. The percentage of cross-shore current variance at the array estimated unresolvable high mode is less than 35%, with one exception for which approximately 50% of the variance is mode 0 across a subs...

Journal ArticleDOI
TL;DR: In this paper, a model that incorporates a five-reaction photochemical scheme and the complete dynamics of linearized acoustic-gravity waves in an isothermal, motionless atmosphere is presented.
Abstract: Wave-induced temporal fluctuations in the intensity of the OH nightglow are related to the temperature oscillations of the wave field by a model that incorporates a five-reaction photochemical scheme and the complete dynamics of linearized acoustic-gravity waves in an isothermal, motionless atmosphere. The intensity I and rotational temperature T oscillations, δI and δT, are conveniently related by the ratio, where the overbar refers to time-averaged quantities. The ratio η is a complex quantity that depends on the properties of the basic state atmosphere (temperature, thermodynamic parameters, major constituent O2, N2 and minor constituent O, O3, OH, H, HO2 concentrations, and scale heights), chemical reaction rate constants, wave period, horizontal wavelength, and direction of wave energy propagation (upward or downward). The intensity-temperature oscillation ratio η is evaluated for a nominal case corresponding to an altitude of about 83 km in a nightside model atmosphere with an atomic oxygen scale height of −2.8 km; horizontal wavelength λx is 100 km, and wave energy propagation is upward. Over a broad range of acoustic periods |η| varies between 7 and 8, and η is approximately in phase with the temperature fluctuations. At gravity wave periods, |η| decreases with increasing period from a maximum value of about 7.0; at a period of about 3 hours, |η| is about 1.8. The phase of η and δT are within 45° in the gravity wave regime. The main effect of order of magnitude changes in λx is the modification of the location and width (in period) of evanescent regions. At hour periods, |η| increases as the magnitude of atomic oxygen scale height decreases; at periods of several hours, |η| is about 1/3 greater for an atomic oxygen scale height of −2 km than for the nominal scale height. The amplitude of η is essentially independent of the direction of wave energy propagation, but the phase of η relative to that of δT depends on the upward or downward sense of energy propagation at periods in close proximity to the evanescent regime. The magnitude of η at gravity wave periods can depend sensitively on the altitude of the OH emission layer; higher OH emission heights give smaller values of |η| at 10-min periods, providing the O3 scale height is not too great. Neglect of minor constituent photochemistry in computing η is a tolerable approximation at acoustic wave periods, but it is entirely inadequate at gravity wave periods. Inclusion of dynamical effects is absolutely essential for a valid assessment of η at any period.

01 May 1987
TL;DR: In this article, an analytical model is developed for the opposition effects in the case of light scattering from a semi-infinite, particulate medium with particles that are large relative to the wavelength.
Abstract: An analytical model is developed for the opposition effects (heiligenshein) in the case of light scattering from a semi-infinite, particulate medium with particles that are large relative to the wavelength. The effect is common for natural materials, and comprises a bright surge in light diffusively reflected from a surface at near zero phase. A generalized expression is devised for the extinction coefficient of a particulate medium. Models are developed for step function and hyperbolic tangent distributions of light scattered from a stratified medium and exhibiting the opposition effect. A maximum brightness amplitude increase of 0.753 is projected for the effect. Greater values must have other causes. To illustrate the theory it is fitted to observations of the Moon, an asteroid, and a satellite of Uranus; Europa is also discussed.

Journal ArticleDOI
TL;DR: In this article, a dynamic reflection interference contrast (RIC) microscopy is presented by which thermally excitated surface undulations of erythrocyte plasma membranes 2014 the cell flickering 2014 can be evaluated to an amplitude resolution of ~ 50 nm and a wavelength resolution of 0.5 03BCm.
Abstract: 2014 A new method, the dynamic reflection interference contrast (RIC) microscopy is presented by which thermally excitated surface undulations of erythrocyte plasma membranes 2014 the cell flickering 2014 can be evaluated to an amplitude resolution of ~ 50 nm and a wavelength resolution of 0.5 03BCm. The Newtonian interference pattern formed by the interference of light reflected from the cell surface and from the cover glass (to which the cells are slightly fixed) is analysed by a home made fast image processing system. Two evaluation procedures are proposed : firstly the direct reconstruction of the momentaneous surface profile by retransformation of the RIC interference pattern and secondly the Fourier analysis of the interference pattern. In the first case the excitation relief is obtained by subtraction of two momentaneous surface profiles and it is best suited in the long wavelength regime. In the second case the spatial frequency spectrum of the flickering is determined by Fourier transformation of the RIC interference pattern. This technique is reliable in the short wavelength regime and is used here to determine the bending elastic modulus, Kc, in a wave length domain between 0.5 and 1 03BCm. This simultaneous determination of many Kc-values greatly enhances the accuracy of the measurement. This procedure is also suited to test whether the flickering obeys the equipartition law. The elastic constants of normal discocytes, of cup-shaped stomatocytes and of echinocytes are compared. The values of the first two classes are about equal : Kc = 3.4 ± 0.8 x 10-20 Nm and agree well with values reported previously [1]. The last cell shape exhibits a substantial higher stiffness Kc = 13 ± 2 10-20Nm. An outstanding advantage of the dynamic RIC-microscopy is that it allows to measure absolute values of the displacement of the membrane facing the coverslide whereas the conventional flicker spectroscopy [1, 8] can only detect fluctuations of the cell thickness. A second advantage is that it can also be applied to erythrocyte ghosts or to other transparent cells. J. Physique 48 (1987) 2139-2151 DTCEMBRE 1987, Classification Physics Abstracts 87.20 Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphys:0198700480120213900

Journal ArticleDOI
TL;DR: In this paper, a solid-state device capable of continuous detection of individual photons in the wavelength range from 0.4 to 28 μm is described, and its response to the absorption of incident photons consists of submicrosecond rise time pulses with amplitudes well above the electronic readout noise level.
Abstract: A solid‐state device capable of continuous detection of individual photons in the wavelength range from 0.4 to 28 μm is described. Operated with a dc applied bias, its response to the absorption of incident photons consists of submicrosecond rise time pulses with amplitudes well above the electronic readout noise level. A counting quantum efficiency of over 30% has been demonstrated at a wavelength of 20 μm, and over 50% was observed in the visible‐light region. Optimum photon‐counting performance occurs for temperatures between 6 and 10 K and for count rates less than 1010 counts/s per cm2 of detector area. The operating principle of the device is outlined and its performance characteristics as a photon detector are presented.

Journal ArticleDOI
TL;DR: In this article, the authors examined the mode and direction of wave propagation at Comet Giacobini-Zinner and provided important constraints on potential mechanisms for the wave origin in the vicinity of the comet.
Abstract: Intense MHD waves at Comet Giacobini-Zinner were examined to investigate the mode and direction of wave propagation and thereby to provide important constraints on potential mechanisms for the wave origin in the vicinity of the comet. From observations of steepened wave forms, it is found that the waves must be propagating toward the sun but are blown back across the ICE spacecraft. The correlation between magnetic field magnitude and electron density enhancements indicates that these waves are fast magnetosonic mode emissions. The sense of rotation of the partial rotations are left-hand circularly polarized in the spacecraft frame, consistent with anomalously Doppler-shifted right-hand waves.

Journal ArticleDOI
TL;DR: In this article, images of wave-like structure in three nightglow emissions with different height profiles [the OI (557.7 nm) and Na (589.2 nm) lines and the OH bands between 715 and 810 nm] have been obtained with a low light TV system.

Journal ArticleDOI
TL;DR: In this paper, a Fourier transform spectrometer designed to operate at high resolution at wavelengths down to 170 nm is described, and the principal instrumental parameters are: mirror travel, 200 mm; resolving limit, 0.025 cm-1; collimator aperture ratio, f/25; overall dimensions of vacuum tank, 1.5 m*0.25 m *0.
Abstract: A Fourier transform spectrometer designed to operate at high resolution at wavelengths down to 170 nm is described. The principal instrumental parameters are: mirror travel, 200 mm; resolving limit, 0.025 cm-1; collimator aperture ratio, f/25; overall dimensions of vacuum tank, 1.5 m*0.25 m*0.25 m. Test results show (i) a signal-to-noise ratio in the transformed spectrum at 200 nm better than 1000:1 for an iron-neon hollow cathode lamp at a resolving power of quarter of a million, (ii) fully resolved line profiles in the same source at a resolving limit of 0.03 cm-1 (resolving power 1.5*106), (iii) relative wavenumbers of Fe II emission lines reproducible to +or-0.0006 cm-1 (3.4 fm), and (iv) a significant luminosity gain over grating spectrometers operating in the same region.

Journal ArticleDOI
TL;DR: In this paper, the optical transmission spectra of thin samples of Ag-Ge30S70 were analyzed on the basis of a uniform distribution of dissolved Ag. The amount of photodoped Ag is quantitatively estimated from values of ln [T(t)/T(0) where T(t) is the transmission after exposure to light for time t.
Abstract: Photodoping in a thin sample of Ag–Ge30S70 was studied by an optical transmission measurement. Changes in the optical transmission spectra were analyzed on the bases of a uniform distribution of dissolved Ag. This study suggests that the spectra of thin samples are not modulated by the interference effect over a wavelength range of 350–800 nm. The amount of photodoped Ag is quantitatively estimated from values of ln [T(t)/T(0)], where T(t) is the transmission after exposure to light for time t. There is a specific wavelength at which the transmission is practically independent of the irradiation time; traces of the spectra reach a point at this wavelength. This point is called an isotransmission point and is denoted λ*. The condition that λ* appears in the spectra was derived theoretically. The isotransmission point is useful for estimating the thicknesses of an Ag-doped layer.

Journal ArticleDOI
TL;DR: Anomalously fast ion heating has been observed in the Caltech Encore tokamak [Phys. Rev. Lett. 59, 1436] with the use of laser-induced fluorescence.
Abstract: Anomalously fast ion heating has been observed in the Caltech Encore tokamak [Phys. Rev. Lett. 59, 1436 (1987)], with the use of laser-induced fluorescence. This heating was found to be independent of electron temperature, but was well correlated with the presence of large-amplitude drift-Alfven waves. Evidence is presented that suggests that the heating is stochastic and occurs when the ion displacement due to polarization drift becomes comparable to the perpendicular wavelength, i.e., when k[perpendicular] (mik[perpendicular] phi0/qB^2)~1. Stochastic heating may also be the cause of the anomalously high ion temperatures observed in reversed-field pinches.

Journal ArticleDOI
TL;DR: In this article, a four-port optical tap that extracts efficiently from a fiber in which light containing several discrete wavelength bands is propagating only that light within one such band was proposed.
Abstract: A novel design is proposed for a four-port optical tap that extracts efficiently from a fibre in which light containing several discrete wavelength bands is propagating only that light within one such band. The same device can be used simultaneously to combine light of the same wavelength as the extracted light with the other, unselected, wavelength bands.

Journal ArticleDOI
TL;DR: In this paper, an analysis of small-scale artificial ionospheric turbulence (SAIT) arising near the level at which a powerful wave is reflected with ordinary polarization is presented. But the authors are primarily concerned with SAIT with inhomogeneities that are greatly extended along the geomagnetic field with transverse dimensions that are less than the wavelengths of the perturbing waves -the pumping waves (PW) in a vacuum.
Abstract: This study is an analysis of artificial ionospheric turbulence (AIT) arising near the level at which a powerful wave is reflected with ordinary polarization. AIT is an inhomogeneous structure in the ionosphere with a size on the order of centimeters or tens of kilometers and with characteristic frequencies from a fraction of a hertz (aperiodic inhomogeneity) to several megahertz (plasma waves). The authors are primarily concerned with small-scale artificial ionospheric turbulence (SAIT), i.e., with inhomogeneities that are greatly extended along the geomagnetic field with transverse dimensions that are less than the wavelengths of the perturbing waves - the pumping waves (PW) - in a vacuum.

Journal ArticleDOI
TL;DR: In this paper, an expression for optical visibility during storms is given in terms of the relative volume occupied by dust, and expressions for attenuation and phase shift constants for a medium with precipitating dust particles are derived in terms both of visibility and wavelength for both vertical and horizontal polarizations.
Abstract: Some of the electrical and mechanical properties of dust are discussed. An expression for optical visibility during storms is given in terms of the relative volume occupied by dust. Expressions for attenuation and phase shift constants for a medium with precipitating dust particles are derived in terms of visibility and wavelength for both vertical and horizontal polarizations. Expressions for the attenuation and cross polarization of circularly polarized waves are also derived. Computations show that linearly polarized waves suffer but little effect. Circularly polarized waves on the other hand are significantly cross polarized.