Laser Stabilization at 1536 nm Using Regenerative Spectral Hole Burning

Laser frequency stabilization giving a 500-Hz Allan deviation for a 2-ms integration time with drift reduced to 7 kHz/min over several minutes was achieved at 1536 nm in the optical communication band. A continuously regenerated spectral hole in the inhomogeneously broadened 4I15/2(1)!4I13/2(1) optical absorption of an Er31:Y2SiO5 crystal was used as the short-term frequency reference, while a variation on the locking technique allowed simultaneous use of the inhomogeneously broadened absorption line as a long-term reference. The reported frequency stability was achieved without vibration isolation. Spectral hole burning frequency stabilization provides ideal laser sources for high-resolution spectroscopy, real-time optical signal processing, and a range of applications requiring ultra-narrow-band light sources or coherent detection; the time scale for stability and the compatibility with spectral hole burning devices make this technique complementary to other frequency references for laser stabilization

Discharge and force distribution in a sinuous channel with vegetated floodplains during overbank flow

This is an Accepted Manuscript of an article published by Taylor & Francis Group in Journal of Hydraulic Research on 2019, available online at: http://www.tandfonline.com/10.1080/00221686.2019.1581667Overbank flow in a sinuous channel with roughened floodplains has been investigated, focusing on the effect of floodplain vegetation on overall flow resistance. The physical model of the Besòs River has allowed analysing the effect of flexible roughness elements which simulate the natural vegetation of rivers. The experimental measurements of horizontal velocities have been used to obtain zonal discharges and forces along a meander wavelength. The results illustrate that although mass transfer is the most important source of energy losses, in rivers with strongly vegetated floodplains the flow resistance increases considerably due to the strong apparent shear forces acting between the main channel and floodplains.Peer ReviewedPostprint (author's final draft

Measurement of the Ratio of Double-to-Single Photoionization of Helium at 2.8 keV Using Synchrotron Radiation

We report the first measurement of the ratio of double-to-single photoionization of helium well above the double-ionization threshold. Using a time-of-flight technique, we find He++/He+=1.6±0.3% at hν=2.8 keV. This value lies between calculations by Amusia (2.3%) and by Samson, who predicts 1.2% by analogy with electron-impact ionization cross sections of singly charged ions. Good agreement is obtained with older shake calculations of Byron and Joachain, and of Åberg, who predict 1.7%

Compton double-to-single ionization ratio of helium at 57 keV

We have measured the Compton double-to-single ionization ratio of helium using an ion time-of-flight spectrometer along with monochromatized synchrotron radiation of 57 keV. This photon energy is high and probes the Compton ionization alone, since the photoionization makes only a negligible contribution to the total cross section. Comparing our result, which is (1.25±0.3)%, with theoretical calculations and measurements at lower energies shows that this energy is most likely still not high enough to confirm the value of the asymptotic high-energy limit experimentally

Argon-photoion–Auger-electron Coincidence Measurements Following K-shell Excitation by Synchrotron Radiation

Argon photoion spectra have been obtained for the first time in coincidence with K-LL and K-LM Auger electrons, as a function of photon energy. The simplified charge distributions which result exhibit a much more pronounced photon-energy dependence than do the more complicated noncoincident spectra. In the near-K-threshold region, Rydberg shakeoff of np levels, populated by resonant excitation of K electrons, occurs with significant probability, as do double-Auger processes and recapture of the K photoelectron through postcollision interaction

Dynamical Relativistic Effects in Photoionization: Spin-Orbit-Resolved Angular Distributions of Xenon 4d Photoelectrons Near the Cooper Minimum

Two decades ago, it was predicted [Y. S. Kim et al., Phys. Rev. Lett. 46, 1326 (1981)] that relativistic effects should alter the dynamics of the photoionization process in the vicinity of Cooper minima. The present experimental and theoretical study of the angular distributions of Xe 4d3/2 and 4d5/2 photoelectrons demonstrates this effect for the first time. The results clearly imply that relativistic effects are likely to be important for intermediate- Z atoms at most energies

Relativistic Hartree-Bogoliubov description of the deformed ground-state proton emitters

Ground-state properties of deformed proton-rich odd-Z nuclei in the region $59 \leq Z \leq 69$ are described in the framework of Relativistic Hartree Bogoliubov (RHB) theory. One-proton separation energies and ground-state quadrupole deformations that result from fully self-consistent microscopic calculations are compared with available experimental data. The model predicts the location of the proton drip-line, the properties of proton emitters beyond the drip-line, and provides information about the deformed single-particle orbitals occupied by the odd valence proton.Comment: 9 pages, RevTeX, 3 PS figures, submitted Phys. Rev. Letter

High-energy Behavior of the Double Photoionization of Helium from 2 to 12 keV

We report the ratio of double-to-single photoionization of He at several photon energies from 2 to 12 keV. By time-of-Aight methods, we find a ratio consistent with an asymptote at 1.5%±0.2%, essentially reached by h v≈4 keV. Fair agreement is obtained with older shake calculations of Byron and Joachain [Phys. Rev. 164, 1 (1967)], of Aberg [Phys. Rev. A 2, 1726 (1970)], and with recent many-body perturbation theory (MBPT) of Ishihara, Hino, and McGuire [Phys. Rev. A 44, 6980 (1991)]. The result lies below earlier MPBT calculations by Amusia et al. [J. Phys. B 8, 1248 (1975)] (2.3%), and well above semiempirical predictions of Samson [Phys. Rev. Lett. 65, 2861 (1990)], who expects no asymptote and predicts ơ(He2+)/ơ (He+) =0.3% at 12 keV

Gain without population inversion in V-type systems driven by a frequency-modulated field

We obtain gain of the probe field at multiple frequencies in a closed three-level V-type system using frequency modulated pump field. There is no associated population inversion among the atomic states of the probe transition. We describe both the steady-state and transient dynamics of this system. Under suitable conditions, the system exhibits large gain simultaneously at series of frequencies far removed from resonance. Moreover, the system can be tailored to exhibit multiple frequency regimes where the probe experiences anomalous dispersion accompanied by negligible gain-absorption over a large bandwidth, a desirable feature for obtaining superluminal propagation of pulses with negligible distortion.Comment: 10 pages + 8 figures; To appear in Physical Review

An Integrated and Novel Approach to Estimating the Conveyance Capacity of the River Blackwater

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv