It is generally believed that the recollision mechanism of atomic nonsequential double ionization is suppressed in circularly polarized laser fields because the returning electron is unlikely to ...encounter the core. On the contrary, we find that recollision can and does significantly enhance double ionization, even to the extent of forming a "knee," the signature of the nonsequential process. Using a classical model, we explain two apparently contradictory experiments, the absence of a knee for helium and its presence for magnesium.
We show that a family of key periodic orbits drives the recollision process in a strong circularly polarized laser field. These orbits, coined recolliding periodic orbits, exist for a wide range of ...parameters, and their relative influence changes as the laser and atomic parameters are varied. We find the necessary conditions for recollision-driven nonsequential double ionization to occur. The outlined mechanism is universal in that it applies equally well beyond atoms: The internal structure of the target species plays a minor role in the recollision process.
We identify the phase-space structures that regulate atomic double ionization in strong ultrashort laser pulses. The emerging dynamical picture complements the recollision scenario by clarifying the ...distinct roles played by the recolliding and core electrons, and leads to verifiable predictions on the characteristic features of the "knee", a hallmark of the nonsequential process.
We present a purely classical recollision scenario, i.e., without tunneling, which, in contrast to the standard three-step model, takes into account the ionic core potential fully at all stages of ...the recollision process and is valid at all intensities. We find that a key periodic orbit drives the recollisions by guiding electrons away and back to the core. At sufficiently high intensity, we connect our scenario to the three-step model, and explain why the three-step model leads to good agreement with the cutoff in high harmonic generation despite neglecting the core potential after tunneling.
We examine the nature and statistical properties of electron-electron collisions in the recollision process in a strong laser field. The separation of the double ionization yield into sequential and ...nonsequential components leads to a bell-shaped curve for the nonsequential probability and a monotonically rising one for the sequential process. We identify key features of the nonsequential process and connect our findings in a simplified model which reproduces the knee shape for the probability of double ionization with laser intensity and associated trends.
The possibility to probe new physics scenarios of light Majorana neutrino exchange and right-handed currents at the planned next generation neutrinoless double
β
decay experiment SuperNEMO is ...discussed. Its ability to study different isotopes and track the outgoing electrons provides the means to discriminate different underlying mechanisms for the neutrinoless double
β
decay by measuring the decay half-life and the electron angular and energy distributions.
To study the epidemiology, clinical observations, and microbiologic characteristics of fungal keratitis at tertiary eye care centers in the United States.
Retrospective multicenter case series.
...Fungal keratitis cases presenting to participating tertiary eye care centers.
Charts were reviewed for all fungal keratitis cases confirmed by culture, histology, or confocal microscopy between January 1, 2001, and December 31, 2007, at 11 tertiary clinical sites in the United States.
Frequency of potential predisposing factors and associations between these factors and fungal species.
A total of 733 cases of fungal keratitis were identified. Most cases were confirmed by culture from corneal scraping (n = 693) or biopsies (n = 19); 16 cases were diagnosed by microscopic examination of corneal scraping alone; and 5 cases were diagnosed by confocal microscopy alone. Some 268 of 733 cases (37%) were associated with refractive contact lens wear, 180 of 733 cases (25%) were associated with ocular trauma, and 209 of 733 cases (29%) were associated with ocular surface disease. No predisposing factor was identified in 76 cases (10%). Filamentous fungi were identified in 141 of 180 ocular trauma cases (78%) and in 231 of 268 refractive contact lens-associated cases (86%). Yeast was the causative organism in 111 of 209 cases (53%) associated with ocular surface disease. Yeast accounted for few cases of fungal keratitis associated with refractive contact-lens wear (20 cases), therapeutic contact-lens wear (11 cases), or ocular trauma (21 cases). Surgical intervention was undertaken in 26% of cases and was most frequently performed for fungal keratitis associated with ocular surface disease (44%). Surgical intervention was more likely in cases associated with filamentous fungi (P = 0.03). Among contact lens wearers, delay in diagnosis of 2 or more weeks increased the likelihood of surgery (age-adjusted odds ratio = 2.2; 95% confidence interval, 1.2-4.2).
Trauma, contact lens wear, and ocular surface disease predispose patients to developing fungal keratitis. Filamentous fungi are most frequently the causative organism for fungal keratitis associated with trauma or contact lens wear, whereas yeast is most frequently the causative organism in patients with ocular surface disease. Delay in diagnosis increases the likelihood of surgical intervention for contact lens-associated fungal keratitis.
PDF
