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We investigate the subcycle control of electron trajectories in single ionization of Ar atoms with two-color laser pulses consisting of a linearly polarized 800-nm field and a circularly polarized 400-nm field. By varying the relative phase between the two fields, the photoelectron angular distribution rotates in the polarization plane and the rotation velocity can be controlled. From the comparison with results obtained with a semiclassical model, we find that the Coulomb field has a greater impact on direct trajectories than on those that undergo a recollision which is opposite to the electron behavior in a monochromatic field. This effect can be directly visualized in the experiment and finely controlled on a subcycle timescale by means of the two-color field scheme. It is shown that the influence of the Coulomb force on the photoelectron momentum distribution is different along the longitudinal and transverse direction.

The laser-induced nonsequential double ionization (NSDI) of rare gas atoms in the near and mid-IR laser fields is studied experimentally and theoretically. We investigate electron-electron correlation at high recollision energies, experimentally achieving ponderomotive energies (Up) above 80 eV. The contribution of the two dominant channels of NSDI in the photoelectron momentum distribution, impact, and excitation ionization, are both shown to scale with ponderomotive energy and are well reproduced by theory. Surprisingly, for a large Up in mid-IR fields, a noticeable electron-electron anticorrelation signal emerges at low photoelectron momenta, which cannot be explained by these mechanisms within state-of-the-art theoretical approaches.

Synopsis Using a 4f pulse shaper in combination with a Reaction Microscope we performed 800 nm pump-probe experiments with orthogonally polarized pulses on H₂.

The first hundred attoseconds of the electron dynamics during strong field tunneling ionization are investigated. We quantify theoretically how the electron's classical trajectories in the continuum emerge from the tunneling process and test the results with those achieved in parallel from attoclock measurements. An especially high sensitivity on the tunneling barrier is accomplished here by comparing the momentum distributions of two atomic species of slightly deviating atomic potentials (argon and krypton) being ionized under absolutely identical conditions with near-infrared laser pulses (1300 nm). The agreement between experiment and theory provides clear evidence for a nonzero tunneling time delay and a nonvanishing longitudinal momentum of the electron at the ``tunnel exit.''

Channel-selective electron emission from strong-field photoionization of ${\mathrm{H}}_{2}$ molecules is experimentally investigated by using ultrashort laser pulses and a reaction microscope. The electron momenta and energy spectra in coincidence with bound and dissociative ionization channels are compared. Surprisingly, we observed an enhancement of the photoelectron yield in the low-energy region for the bound ionization channel. By further investigation of asymmetrical electron emission using two-color laser pulses, this enhancement is understood as the population of the autoionizing states of ${\mathrm{H}}_{2}$ molecules in which vibrational energy is transferred to electronic energy. This general mechanism provides access to the vibrational-state distribution of molecular ions produced in a strong-field interaction.

We have combined a tandem mass spectrometer with a 780 nm fs-laser system to study photoionization and photofragmentation of trapped protonated leucine enkephalin cations for laser intensities between 2 × 1013 W/cm2 and 1 × 1014 W/cm2 and pulse durations of 15 fs. In this intensity range, the transition from multiphoton ionization and excitation to tunneling ionization is expected to occur. The observed partial ion yield curves as a function of laser intensity exhibit a power-law dependence, indicating multiphoton absorption to be the dominating mechanism. Pump-probe studies were performed to investigate the time-evolution of the multiphoton ionization process. The partial ion yields of almost all fragmentation channels show a broad but distinct maximum at a delay-time of approximately 750 fs. The particularly flat appearance of the pump-probe curves suggests that not a single resonance, but a broad distribution of resonances is involved.

In this work we explored strong field-induced decay of doubly excited transient Coulomb complex Ar ∗∗ → Ar 2+ + 2e. We measured the correlated two-electron emission as a function of carrier envelop phase (CEP) of 6 fs pulses in the non-sequential double ionization (NSDI) of argon. Classical model calculations suggest that the intermediate doubly excited Coulomb complex loses memory of its formation dynamics. We estimated the ionization time difference between the two electrons from NSDI of argon and it is 200 ± 100 as (N Camus et al, Phys. Rev. Lett. 108, 073003 (2012)).

Channel-selective electron emission from strong-field photoionization of H_{2} molecules is experimentally investigated by using ultrashort laser pulses and a reaction microscope. The electron momenta and energy spectra in coincidence with bound and dissociative ionization channels are compared. Surprisingly, we observed an enhancement of the photoelectron yield in the low-energy region for the bound ionization channel. By further investigation of asymmetrical electron emission using two-color laser pulses, this enhancement is understood as the population of the autoionizing states of H_{2} molecules in which vibrational energy is transferred to electronic energy. This general mechanism provides access to the vibrational-state distribution of molecular ions produced in a strong-field interaction.

Tunneling of a particle through a potential barrier remains one of the most remarkable quantum phenomena. Owing to advances in laser technology, electric fields comparable to those electrons experience in atoms are readily generated and open opportunities to dynamically investigate the process of electron tunneling through the potential barrier formed by the superposition of both laser and atomic fields. Attosecond-time and angstrom-space resolution of the strong laser-field technique allow to address fundamental questions related to tunneling, which are still open and debated: Which time is spent under the barrier and what momentum is picked up by the particle in the meantime? In this combined experimental and theoretical study we demonstrate that for strong-field ionization the leading quantum mechanical Wigner treatment for the time resolved description of tunneling is valid. We achieve a high sensitivity on the tunneling barrier and unambiguously isolate its effects by performing a differential study of two systems with almost identical tunneling geometry. Moreover, working with a low frequency laser, we essentially limit the non-adiabaticity of the process as a major source of uncertainty. The agreement between experiment and theory implies two substantial corrections with respect to the widely employed quasiclassical treatment: In addition to a non-vanishing longitudinal momentum along the laser field-direction we provide clear evidence for a non-zero tunneling time delay. This addresses also the fundamental question how the transition occurs from the tunnel barrier to free space classical evolution of the ejected electron., 31 pages, 15 figures including appendix

Very sharp, low-energy structures observed in photoelectron spectra reveal the population of autoionizing states in krypton and argon in strong laser fields over a large range of different wavelengths. The energies of the electrons, emitted by autoionization in a field-free environment, provide direct information about the spectrum of states involved. Despite their ability to resist ionization by the populating laser pulse, we demonstrate the possibility to promote the excited electrons into the continuum by subsequent absorption of a single photon. Thus, applying a classical pump-probe scheme, we are able to manipulate the autoionization contribution on a picosecond time scale. Different scenarios for the creation of autoionizing states in strong laser fields are discussed.

We present a joint experimental and theoretical study of ionization of argon atoms by a linearly polarized two-color laser field (800 nm, 400 nm). Changing the relative phase between the two colors, the forward-backward asymmetry of the doubly differential momentum distribution of emitted electrons can be controlled. We nd excellent agreement between the measurements and the solution of the time-dependent Schrodinger equation in the single-active electron approximation. Surprisingly, we also nd good agreement between the quantum and classical calculations of electron momentum distributions generated by lasers at optical wavelengths. Fil: Arbo, Diego. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina Fil: Lemell, C.. Vienna University of Technology; Austria Fil: Nagele, S.. Vienna University of Technology; Austria Fil: Camus, N.. Max-Planck-Institut fur Kernphysik; Alemania Fil: Fechner, L.. Max-Planck-Institut fur Kernphysik; Alemania Fil: Krupp, A.. Max-Planck-Institut fur Kernphysik; Alemania Fil: Pfeifer, T.. Max-Planck-Institut fur Kernphysik; Alemania Fil: López, Sebastián David. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina Fil: Moshammer, R.. Max-Planck-Institut fur Kernphysik; Alemania Fil: Burgdörfer, J.. Vienna University of Technology; Austria

Laser-induced tunnel ionization from a coherent superposition of electronic states in Ar+ is studied in a kinematically complete experiment. Within a pump-probe scheme a spin-orbit wave packet is launched through the first ionization step from the neutral species. The multielectron coherent wave packet is probed as a function of time by the second pulse which ionizes the system to Ar++. By measuring delay-dependent electron momentum distributions we directly image the evolution of the nonstationary multielectron wave function. Comparing the results with simulations we test common assumptions about electron momentum distributions and the tunneling process itself.

Strong-field ionisation surprises with richness beyond current understanding despite decade long investigations. Ionisation with mid-IR light has promptly revealed unexpected kinetic energy structures that seem related to unanticipated quantum trajectories of the electrons. We measure first 3D momentum distributions in the deep tunneling regime (γ = 0.3) and observe surprising new electron dynamics of near-zero momentum electrons and extremely low momentum structures, below the eV, despite very high quiver energies of 95 eV. Such level of high-precision measurements at only 1 meV above the threshold, despite 5 orders higher ponderomotive energies, has now become possible with a specifically developed ultrafast mid-IR light source in combination with a reaction microscope, thereby permitting a new level of investigations into mid-IR recollision physics.

We present a comparative study of nonsequential double ionization (NSDI) of N${}_{2}$ and Ar exposed to near-single-cycle laser pulses. The NSDI process is investigated using carrier-envelope-phase-tagged electron-ion coincidence spectroscopy. The measured NSDI spectra of N${}_{2}$ and Ar exhibit a striking resemblance. In particular, the correlated two-electron momentum distribution arising from NSDI of N${}_{2}$ also displays a cross-shape very similar to that reported for Ar [Bergues et al., Nat. Commun. 3, 813 (2012)]. We interpret our results in terms of recollision-excitation with subcycle depletion and discuss how this mechanism accounts for the observed similarities and differences in the ionization behavior of the two species.

The ultra-fast dynamics of He nanodroplets (103–105 atoms) in intense (1…7 ×1014 W/cm2), few-cycle (∼10 fs), infrared (∼790 nm) laser pulses has been investigated as a function of the number of dopant rare-gas atoms, the laser intensity and the rare-gas species. We find the “ignition” behaviour predicted by theory for 20 fs resulting in the complete ionisation and disintegration of the droplet, otherwise entirely transparent, initiated by just a few, less than 5 dopant atoms.

The strong-field induced decay of a doubly excited, transient Coulomb complex ${\mathrm{Ar}}^{**}\ensuremath{\rightarrow}{\mathrm{Ar}}^{2+}+2{e}^{\ensuremath{-}}$ is explored by tracing correlated two-electron emission in nonsequential double ionization of Ar as a function of the carrier-envelope phase. Using $l6\text{ }\text{ }\mathrm{fs}$ pulses, electron emission is essentially confined to one optical cycle. Classical model calculations support that the intermediate Coulomb complex has lost memory of its formation dynamics and allows for a consistent, though model-dependent definition of ``emission time,'' empowering us to trace transition-state two-electron decay dynamics with sub-fs resolution. We find a most likely emission time difference of $\ensuremath{\sim}200\ifmmode\pm\else\textpm\fi{}100$ as.

Five members of the Le Camus family of Paris were apothecary-grocers, a situation passed down from father to son from the end of the reign of Charles VII up to the reign of Louis XIV, in other words for nearly two centuries. Four of them were called Nicolas and the fifth Jehan. Nicolas I practised his trade in the Rue Saint-Antoine; Nicolas II and Jehan lived in the district of Les Halles, on the corner of the Rue Saint-Denis and the Rue de la Chanvrerie. Nicolas IV was a tenant in a house at the crossroads of the Rue Saint-Honoré and the Rue des Poulies, later absorbed by the opening of the Rue du Louvre. In 1638, Nicolas IV bought the house known as "Le Pavillon des Singes" on the corner of the Rue Saint-Honoré and the Rue des Vieilles Etuves (now the Rue Sauval), the home of the family of Jean Pocquelin, father of Jean-Baptiste, the future Molière. When Nicolas IV died, his goods were divided between his son François, lawyer in Parliament, and his daughter Anne who inherited the "Pavillon des Singes". In 1680, she sold it to an administrator of the Hôtel-Dieu. Nicolas IV Le Camus was the last Parisian apothecary of this dynasty and no other Le Camus practised pharmacy in Paris until the Royal Declaration of 25th April 1777 which created the College of Pharmacy and the Master of Pharmacy.

We demonstrate ultrafast resonant energy absorption of rare-gas doped He nanodroplets from intense few-cycle (~10 fs) laser pulses. We find that less than 10 dopant atoms "ignite" the droplet to generate a non-spherical electronic nanoplasma resulting ultimately in complete ionization and disintegration of all atoms, although the pristine He droplet is transparent for the laser intensities applied. Our calculations at those intensities reveal that the minimal pulse length required for ignition is about 9 fs.

Objective: To compare the 28-day mortality and hospital length of stay of patients with community-acquired pneumonia who were transferred to an intensive care unit on the same day of emergency department presentation (direct-transfer patients) with those subsequently transferred within 3 days of presentation (delayed-transfer patients). Design: Secondary analysis of the original data from two North American and two European prospective, multicenter, cohort studies of adult patients with community-acquired pneumonia. Patients: In all, 453 non-institutionalized patients transferred within 3 days of emergency department presentation to an intensive care unit were included in the analysis. Supplementary analysis was restricted to patients without an obvious indication for immediate transfer to an intensive care unit. Interventions: None. Measurements and Main Results: The sample consisted of 138 delayed-transfer and 315 direct-transfer patients, among whom 150 (33.1%) were considered to have an obvious indication for immediate intensive care unit admission. After adjusting for the quintile of propensity score, delayed intensive care unit transfer was associated with an increased odds ratio for 28-day mortality (2.07; 95% confidence interval, 1.12-3.85) and a decreased odds ratio for discharge from hospital for survivors (0.53; 95% confidence interval, 0.39-0.71). In a propensity-matched analysis, delayed-transfer patients had a higher 28-day mortality rate (23.4% vs. 11.7%; p = 0.02) and a longer median hospital length of stay (13 days vs. 7 days; p

International audience; ABSTRACT: INTRODUCTION: To identify risk factors for early (< three days) intensive care unit (ICU) admission of patients hospitalised with community-acquired pneumonia (CAP) and not requiring immediate ICU admission, and to stratify the risk of ICU admission on days 1 to 3. METHODS: Using the original data from four North American and European prospective multicentre cohort studies of patients with CAP, we derived and validated a prediction rule for ICU admission on days 1 to 3 of emergency department (ED) presentation, for patients presenting with no obvious reason for immediate ICU admission (not requiring immediate respiratory or circulatory support). RESULTS: A total of 6560 patients were included (4593 and 1967 in the derivation and validation cohort, respectively), 303 (4.6%) of whom were admitted to an ICU on days 1 to 3. The Risk of Early Admission to ICU index (REA-ICU index) comprised 11 criteria independently associated with ICU admission: male gender, age younger than 80 years, comorbid conditions, respiratory rate of 30 breaths/minute or higher, heart rate of 125 beats/minute or higher, multilobar infiltrate or pleural effusion, white blood cell count less than 3 or 20 G/L or above, hypoxaemia (oxygen saturation < 90% or arterial partial pressure of oxygen (PaO2) < 60 mmHg), blood urea nitrogen of 11 mmol/L or higher, pH less than 7.35 and sodium less than 130 mEq/L. The REA-ICU index stratified patients into four risk classes with a risk of ICU admission on days 1 to 3 ranging from 0.7 to 31%. The area under the curve was 0.81 (95% confidence interval (CI) = 0.78 to 0.83) in the overall population. CONCLUSIONS: The REA-ICU index accurately stratifies the risk of ICU admission on days 1 to 3 for patients presenting to the ED with CAP and no obvious indication for immediate ICU admission and therefore may assist orientation decisions.

Experimental results and theoretical analysis of the ionization process of argon atoms interacting with linearly polarized two-color fields (λ1 = 800 nm, λ2 = 400 nm) are presented. We observe complex asymmetry patterns in the measured three-dimensional momentum distributions.

We experimentally investigated the asymmetry of photo-ion and photoelectron momentum spectra of argon and nitrogen by ionizing an argon-nitrogen gas mixture in a strong two-color (400 nm + 800 nm) laser field. By changing the time delay between the 400 nm laser pulse and the 800 nm pulse, the fan-like stripes in low-energy electron momentum shift from negative momentum to positive for both argon and nitrogen. A clear difference of asymmetric electron emission between Ar and N2 is observed.

Recent observations of three unique peaks near 1 eV, 100 meV and 1 meV in the electron spectra generated by ionization using intense mid-IR pulses have challenged the current understanding of strong-field (SF) ionization. The results came as a surprise as they could not be reproduced by the standard version of the commonly used SF approximation. We present results showing the simultaneous measurement of all three low energy ranges at high resolution. This capability is possible due to a unique experimental combination of a high repetition rate mid-IR source, which allows probing deep in the quasi-static regime at high data rates, with a reaction microscope, which allows high resolution three dimensional imaging of the electron momentum distribution.

The advent of mid-IR laser sources (λ ≥ 3.0 μm) permits scrutinizing strong-field photoionization of atoms and molecules deep into the tunnelling regime and unexpected features are being revealed [1]. A low kinetic energy structure (LES) was observed in the experimental photoelectron energy distribution and it was conspicuously absent in semi-classical and Keldysh-Faisal-Reiss (KFR) calculations. Further measurements are required revealing a full 3D momentum picture of the before-mentioned effects.

We present kinematically complete high resolution photoionization measurements in the deep tunneling regime (γ = 0.3) by ultra-short, low-frequency fields (3.1 μm) and unravel momentum contributions of LES, VLES and find a new zero energy structure (ZES).