Polarization of Lyman-β radiation from atomic hydrogen excited by electron impact from near-threshold energy to 1000 eV

The polarization of Lyman-β radiation, produced by electron-impact excitation of atomic hydrogen, has been measured over the extended energy range from near threshold to 1000 eV. Measurements were obtained in a crossed-beams experiment using a silica-reflection linear polarization analyzer in tandem with a vacuum ultraviolet monochromator to isolate the emitted line radiation. Our data are in excellent agreement with convergent close-coupling calculations over the entire energy range. The data are broadly similar to the earlier measurements of H Lyman-α polarization reported from the Jet Propulsion Laboratory

Responses of Problematic Algae to Copper-based Algaecide

Eutrophication is the process by which a body of water acquires a high concentration of nutrients, especially phosphates and nitrates. These typically promote excessive growth of algae. As the algae die and decompose, high levels of organic matter and the decomposing organisms deplete the water of available oxygen, causing the death of other organisms, such as fish. Eutrophication is a natural, slow-aging process for a water body, but human activity greatly speeds up the process (USGS.gov). Golf Courses are often fertilized numerous times a year and can be major problem in fertilizer runoff in ponds surrounding the course. In east Texas where rainfall is more abundant then other parts of the state, golf courses are often more affected by algae in their ponds. Our objective is to clear present algae and prevent future algae blooms caused by fertilizer runoff in the ponds at Woodland Hills Golf Club

Recent Decisions

Comments on recent decisions by L. D. Wichmann, Lawrence James Bradley, John F. Beggan, John A. Slevin, Robert P. Mone, and F. James Kane

Wavelength dependent collective effects in the multiphoton ionization of atomic deuterium

This paper presents the results of an experimental investigation into collective effects in the transient plasma formed by multiphoton ionization of atomic deuterium with a pulsed laser. The laser wavelength is varied in a narrow range around 243 nm, so that the photoionization is resonant with the metastable 2S1/2 state. The ion yield, the ion time-of-flight spectra, and the yield of Lyman-a photons have been measured as a function of laser intensity ~from 1 to 340 MW/cm2! and laser detuning around the 1S1/2-2S1/2 two-photon resonance. During and shortly after the laser pulse, collective effects resulting from the mutual interaction of the photoelectrons and the ions affect the spatial and temporal distribution of the ions. Because of the near-degeneracy of the 2S1/2, 2P1/2 , and 2P3/2 states, the resonant multiphoton ionization is affected by the Stark mixing of these states in the collective field. As a result, the time-dependent yields of ions and of Lyman-a photons are modulated by the interplay of the multiphoton ionization of the atoms and the collective effects in the plasma. From the measurements it is deduced that collective effects are important above a critical charge density of 33108 ions/cm3. An asymmetry is observed in the line profile of the total ion yield as a function of laser detuning. This asymmetry is interpreted to be due to the effect of the collective field upon the intermediate resonant 2S1/2 state of the photoionization process

Wavelength dependent collective effects in the multiphoton ionization of atomic deuterium

This paper presents the results of an experimental investigation into collective effects in the transient plasma formed by multiphoton ionization of atomic deuterium with a pulsed laser. The laser wavelength is varied in a narrow range around 243 nm, so that the photoionization is resonant with the metastable 2S1/2 state. The ion yield, the ion time-of-flight spectra, and the yield of Lyman-a photons have been measured as a function of laser intensity ~from 1 to 340 MW/cm2! and laser detuning around the 1S1/2-2S1/2 two-photon resonance. During and shortly after the laser pulse, collective effects resulting from the mutual interaction of the photoelectrons and the ions affect the spatial and temporal distribution of the ions. Because of the near-degeneracy of the 2S1/2, 2P1/2 , and 2P3/2 states, the resonant multiphoton ionization is affected by the Stark mixing of these states in the collective field. As a result, the time-dependent yields of ions and of Lyman-a photons are modulated by the interplay of the multiphoton ionization of the atoms and the collective effects in the plasma. From the measurements it is deduced that collective effects are important above a critical charge density of 33108 ions/cm3. An asymmetry is observed in the line profile of the total ion yield as a function of laser detuning. This asymmetry is interpreted to be due to the effect of the collective field upon the intermediate resonant 2S1/2 state of the photoionization process

A polarized atomic hydrogen beam

We describe the design and operating characteristics of a simple polarized atomic hydrogen beam particularly suitable for applications to crossed beams experiments. In addition to experimental measurements, we present the results of detailed computer models, using Monte-Carlo ray tracing techniques, optical analogs, and phase-space methods, that not only provide us with a confirmation of our measurement, but also allow us to characterize the density, polarization, and atomic fraction of the beam at all points along its path. As a subsidiary result, we also present measurements of the relative and absolute efficiencies of the V/G Supavac mass analyzer for masses 1 and 2

Polarization Correlation Measurements of Electron Impact Excitation of Hs2pd at 54.4 eV

First direct measurements are reported of the linear reduced Stokes parameters P1,P2 for H(2p) excited by electron impact at the benchmark energy of 54.4 eV. The results differ significantly from previous values deduced from angular correlation measurements which are in serious conflict with all sophisticated theoretical approaches. Our results support the trend of theoretical predictions for P2 and confirm that its value is negative at electron scattering angles above 100±, as predicted by theory

Polarization Correlation Measurements of Electron Impact Excitation of Hs2pd at 54.4 eV

First direct measurements are reported of the linear reduced Stokes parameters P1,P2 for H(2p) excited by electron impact at the benchmark energy of 54.4 eV. The results differ significantly from previous values deduced from angular correlation measurements which are in serious conflict with all sophisticated theoretical approaches. Our results support the trend of theoretical predictions for P2 and confirm that its value is negative at electron scattering angles above 100±, as predicted by theory

Atomic, Molecular, and Optical Physics: Optical Excitation Function of H(1s-2p) Produced by electron Impact from Threshold to 1.8 keV

The optical excitation function of prompt Lyman-Alpha radiation, produced by electron impact on atomic hydrogen, has been measured over the extended energy range from threshold to 1.8 keV. Measurements were obtained in a crossed-beams experiment using both magnetically confined and electrostatically focused electrons in collision with atomic hydrogen produced by an intense discharge source. A vacuum-ultraviolet mono- chromator system was used to measure the emitted Lyman-Alpha radiation. The absolute H(1s-2p) electron impact excitation cross section was obtained from the experimental optical excitation function by normalizing to the accepted optical oscillator strength, with corrections for polarization and cascade. Statistical and known systematic uncertainties in our data range from +/- 4% near threshold to +/- 2% at 1.8 keV. Multistate coupling affecting the shape of the excitation function up to 1 keV impact energy is apparent in both the present experimental data and present theoretical results obtained with convergent close- coupling (CCC) theory. This shape function effect leads to an uncertainty in absolute cross sections at the 10% level in the analysis of the experimental data. The derived optimized absolute cross sections are within 7% of the CCC calculations over the 14 eV-1.8 keV range. The present CCC calculations converge on the Bethe- Fano profile for H(1s-2p) excitation at high energy. For this reason agreement with the CCC values to within 3% is achieved in a nonoptimal normalization of the experimental data to the Bethe-Fano profile. The fundamental H(1s-2p) electron impact cross section is thereby determined to an unprecedented accuracy over the 14 eV - 1.8 keV energy range