The effect of electron-electron correlation on the attoclock experiment

We investigate multi-electron effects in strong-field ionization of Helium using a semi-classical model that, unlike other commonly used theoretical approaches, takes into account electron-electron correlation. Our approach has an additional advantage of allowing to selectively switch off different contributions from the parent ion (such as the remaining electron or the nuclear charge) and thereby investigate in detail how the final electron angle in the attoclock experiment is influenced by these contributions. We find that the bound electron exerts a significant effect on the final electron momenta distribution that can, however, be accounted for by an appropriately selected mean field. Our results show excellent agreement with other widely used theoretical models done within a single active electron approximation

Ptychographic reconstruction of attosecond pulses

We demonstrate a new attosecond pulse reconstruction modality which uses an algorithm that is derived from ptychography. In contrast to other methods, energy and delay sampling are not correlated, and as a result, the number of electron spectra to record is considerably smaller. Together with the robust algorithm, this leads to a more precise and fast convergence of the reconstruction.Comment: 12 pages, 7 figures, the MATLAB code for the method described in this paper is freely available at http://figshare.com/articles/attosecond_Extended_Ptychographyc_Iterative_Engine_ePIE_/160187

Chromatic transit light curves of disintegrating rocky planets

Context. Kepler observations have revealed a class of short period exoplanets, of which Kepler-1520 b is the prototype, which have comet-like dust tails thought to be the result of small, rocky planets losing mass. The shape and chromaticity of the transits constrain the properties of the dust particles originating from the planet's surface, offering a unique opportunity to probe the composition and geophysics of rocky exoplanets. Aims. We aim to approximate the average Kepler long-cadence light curve of Kepler-1520 b and investigate how the optical thickness and transit cross-section of a general dust tail can affect the observed wavelength dependence and depth of transit light curves. Methods. We developed a new 3D model that ejects sublimating particles from the planet surface to build up a dust tail, assuming it to be optically thin, and used 3D radiative transfer computations that fully treat scattering using the distribution of hollow spheres (DHS) method, to generate transit light curves between 0.45 and 2.5 $\mu$m. Results. We show that the transit depth is wavelength independent for optically thick tails, potentially explaining why only some observations indicate a wavelength dependence. From the 3D nature of our simulated tails, we show that their transit cross-sections are related to the component of particle ejection velocity perpendicular to the planet's orbital plane and use this to derive a minimum ejection velocity of 1.2 kms$^{-1}$. To fit the average transit depth of Kepler-1520 b of 0.87%, we require a high dust mas-loss rate of 7 $-$ 80 M$_\oplus$ Gyr$^{-1}$ which implies planet lifetimes that may be inconsistent with the observed sample. Therefore, these mass-loss rates should be considered to be upper limits.Comment: 22 pages, 22 figures, accepted for publication in A&

Attoclock revisited on electron tunnelling time

The last decade has seen an intense renewed debate on tunnelling time, both from a theoretical and an experimental perspective. Here, we review recent developments and new insights in the field of strong-field tunnel ionization related to tunnelling time, and apply these findings to the interpretation of the attoclock experiment Landsman etal. [Optica2014, 1, 343]. We conclude that models including finite tunnelling time are consistent with recent experimental measurements.Abbreviations: A: adiabatic; ADK: Ammosov, Delone and Krainov model (1, 2); CEO: carrier-envelope-offset phase ; CoM: centre of mass;CTMC: classical trajectory monte carlo simulation; FWHM: full width half maximum; IR: infrared; KR: Keldysh-Rutherford model; NA: non-adiabatic; PMD: photoelectron momentum distribution; PPT: Perelomov, Popov and Terent'ev model (3, 4); SAE: single active electron approximation; SCT: singleclassical trajectory; SFA: strong field approximation; TDSE: time-dependent Schrodinger equatio

Attosecond screening dynamics mediated by electron-localization

Transition metals with their densely confined and strongly coupled valence electrons are key constituents of many materials with unconventional properties, such as high-Tc superconductors, Mott insulators and transition-metal dichalcogenides. Strong electron interaction offers a fast and efficient lever to manipulate their properties with light, creating promising potential for next-generation electronics. However, the underlying dynamics is a fast and intricate interplay of polarization and screening effects, which is poorly understood. It is hidden below the femtosecond timescale of electronic thermalization, which follows the light-induced excitation. Here, we investigate the many-body electron dynamics in transition metals before thermalization sets in. We combine the sensitivity of intra-shell transitions to screening effects with attosecond time resolution to uncover the interplay of photo-absorption and screening. First-principles time-dependent calculations allow us to assign our experimental observations to ultrafast electronic localization on d-orbitals. The latter modifies the whole electronic structure as well as the collective dynamic response of the system on a timescale much faster than the light-field cycle. Our results demonstrate a possibility for steering the electronic properties of solids prior to electron thermalization, suggesting that the ultimate speed of electronic phase transitions is limited only by the duration of the controlling laser pulse. Furthermore, external control of the local electronic density serves as a fine tool for testing state-of-the art models of electron-electron interactions. We anticipate our study to facilitate further investigations of electronic phase transitions, laser-metal interactions and photo-absorption in correlated electron systems on its natural timescale

Simultaneous measurement of the phase noise on all optical modes of a mode-locked laser

We propose and experimentally demonstrate a method to simultaneously measure the relative phase noise of all modes of two mode-locked lasers. The method is based on the numerical analysis of a beat note of two lasers with slightly different pulse repetition rates. We carefully analyze and experimentally demonstrate the potential of this method. Compared to other methods, it has the unique advantage that it provides access to correlations of the phases of different mode

High-energy picosecond Nd:YVO4 slab amplifier for OPCPA pumping

We demonstrate 12-ps pulses with up to 0.6-mJ pulse energy at repetition rates of 50 kHz and 100 kHz from a Nd:YVO4 slab amplifier built in a simple four-pass configuration. Excellent noise performance with pulse energy fluctuations below 0.8% rms has been achieved by using 10-μJ seed pulses from a highly stable industrial laser system and moderate gain (30-46) in the slab amplifie

High prevalence of familial defective apolipoprotein B-100 in Switzerland

Familial defective apolipoprotein B-100 (FDB) is caused by a single G-to-A substitution at nucleotide 10,708 leading to an arginine to glutamine change at amino acid 3,500 of the apolipoprotein B-100 and thus, a reduced binding of the apolipoprotein B to the low density lipoprotein (LDL) receptor. In the present study, the prevalence of FDB in Switzerland was estimated, on the one hand, from a sample of 728 healthy volunteers whose origin was spread out over the entire German, French, and Romansh speaking parts of the country, and, on the other hand, from 142 unrelated Swiss families with primary hypercholesterolemia comprising 520 individuals. Using polymerase chain reaction (PCR)-based methods, three individuals were identified with the point mutation in the sample of volunteers, equivalent to a prevalence of approximately 1/240 (90% confidence interval: 1.51 x 10(-3)-1.03 x 10(-2)). The frequency of FDB in the sample of hypercholesterolemic subjects was 7/142, yielding a prevalence of approximately 1/190 extrapolated to the general population (90% confidence interval: 2.63 x 10(-3)-9.17 x 10(-2)). The combined prevalence based on both samples was 1/209. Thus, the investigated point mutation was highly prevalent in Switzerland and appeared to be more frequent than in other populations studied hitherto. Furthermore, the presence of the mutation was not necessarily associated with an elevation of serum cholesterol levels, particularly in young individuals. While in the non-affected volunteers cholesterol levels increased between the age of 19 and 23 years by 0.22 mmol/l or by 5.6% (P = 0.001), this phenomenon was even more pronounced in individuals with FDB. The three volunteers with the point mutation demonstrated an increase in total cholesterol concentrations by 1.30 mmol/l or by 25% within 2 years, suggesting that, in the early twenties, cholesterol concentrations increase markedly from normal to elevated levels. Considering the estimated high prevalence the relative ease of PCR-based tests, screening for FDB may become a standard procedure in patients with suggested familial forms of hypercholesterolemia

Optical phase noise and carrier-envelope offset noise of mode-locked lasers

The timing jitter, optical phase noise, and carrier-envelope offset (CEO) noise of passively mode-locked lasers are closely related. New key results concern analytical calculations of the quantum noise limits for optical phase noise and CEO noise. Earlier results for the optical phase noise of actively mode-locked lasers are generalized, particularly for application to passively mode-locked lasers. It is found, for example, that mode locking with slow absorbers can lead to optical linewidths far above the Schawlow-Townes limit. Furthermore, mode-locked lasers can at the same time have nearly quantum-limited timing jitter and a strong optical excess phase noise. A feedback timing stabilization via cavity length control can, depending on the situation, reduce or greatly increase the optical phase noise, while not affecting the CEO noise. Besides presenting such findings, the paper also tries to clarify some basic aspects of phase noise in mode-locked laser