154 research outputs found
High-repetition-rate femtosecond optical parametric chirped-pulse amplifier in the mid-infrared
We discuss a dual-stage optical parametric chirped-pulse amplifier generating sub-100-fs pulses in the mid-infrared at a repetition rate of 100 kHz. The system is based on a 1064nm pump laser and a 3-4μm difference frequency generation seed source derived from the output of a femtosecond fiber laser amplifier. Both lasers are commercially available, are diode-pumped, compact, and allow for turn-key operation. Here, we focus our discussion on the design and dimensioning of the optical parametric chirped-pulse amplifier. In particular, we review the available gain materials for mid-infrared generation and analyze the impact of different stretching scenarios. Timing jitter plays an important role in short-pulse parametric amplifier systems and is therefore studied in detail. The geometry of the amplifier stages is optimized through a full 3-dimensional simulation with the aim of maximizing gain bandwidth and output power. The optimized system yields output pulse energies exceeding 1μJ and an overall gain larger than 50 dB. The high repetition rate of the pump laser results in an unprecedented average power from a femtosecond parametric system at mid-infrared wavelengths. First experimental results confirm the design and the predictions of our theoretical mode
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
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
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
Sub-6-fs blue pulses generated by quasi-phase-matching second-harmonic generation pulse compression
Abstract. : We demonstrate a novel scalable and engineerable approach for the frequency-doubling of ultrashort pulses. Our technique is based on quasi-phase-matching and simultaneously provides tailored dispersion and nonlinear frequency conversion of few-cycle optical pulses. The method makes use of the spatial localization of the conversion process and the group velocity mismatch in a chirped grating structure. The total group delay of the nonlinear device can be designed to generate nearly arbitrarily chirped second-harmonic pulses from positively or negatively chirped input pulses. In particular, compressed second-harmonic pulses can be obtained. A brief summary of the underlying theory is presented, followed by a detailed discussion of our experimental results. We experimentally demonstrate quasi-phase-matching pulse compression in the sub-10-fs regime by generating few-cycle pulses in the blue to near-ultraviolet spectral range. Using this new frequency conversion technique, we generate sub-6-fs pulses centered at 405nm by second-harmonic generation from a 8.6fs Ti:sapphire laser pulse. The generated spectrum spans a bandwidth of 220THz. To our knowledge, these are the shortest pulses ever obtained by second-harmonic generatio
Spectral signature of short attosecond pulse trains
We report experimental measurements of high-order harmonic spectra generated
in Ar using a carrier-envelope-offset (CEO) stabilized 12 fs, 800nm laser field
and a fraction (less than 10%) of its second harmonic. Additional spectral
peaks are observed between the harmonic peaks, which are due to interferences
between multiple pulses in the train. The position of these peaks varies with
the CEO and their number is directly related to the number of pulses in the
train. An analytical model, as well as numerical simulations, support our
interpretation
Energy-dependent photoemission delays from noble metal surfaces by attosecond interferometry
How quanta of energy and charge are transported on both atomic spatial and
ultrafast time scales is at the heart of modern technology. Recent progress in
ultrafast spectroscopy has allowed us to directly study the dynamical response
of an electronic system to interaction with an electromagnetic field. Here, we
present energy-dependent photoemission delays from the noble metal surfaces
Ag(111) and Au(111). An interferometric technique based on attosecond pulse
trains is applied simultaneously in a gas phase and a solid state target to
derive surface-specific photoemission delays. Experimental delays on the order
of 100 as are in the same time range as those obtained from simulations. The
strong variation of measured delays with excitation energy in Ag(111), which
cannot be consistently explained invoking solely electron transport or initial
state localization as supposed in previous work, indicates that final state
effects play a key role in photoemission from solids
Attosecond timing of the dynamical Franz–Keldysh effect
To what extent do intra- or inter-band transitions dominate the optical response of dielectrics when pumped by a few-cycle near-infrared transient electric field? In order to find an answer to this question we investigate the dynamical Franz–Keldysh effect in polycrystalline diamond and discuss in detail the attosecond delay of the induced electron dynamics with regard to the driving transient electric field while the peak intensity is varied between 1 × 1012 and 10 × 1012 W cm−2. We found that the main oscillating feature in transient absorption at 43 eV is in phase with the electric field of the pump, to within 49 ± 78 as. However, the phase delay shows a slightly asymmetric V-shaped linear energy dispersion with a rate of about 200 as eV–1. Theoretical calculations within the dipole approximation reproduce the data and allow us to conclude that intra-band motion dominates under our experimental conditions
Ultrafast electron localization and screening in a transition metal dichalcogenide
The coupling of light to electrical charge carriers in semiconductors is the foundation of many technological applications. Attosecond transient absorption spectroscopy measures simultaneously how excited electrons and the vacancies they leave behind dynamically react to the applied optical fields. In compound semiconductors, these dynamics can be probed via any of their atomic constituents. Often, the atomic species forming the compound contribute comparably to the relevant electronic properties of the material. One therefore expects to observe similar dynamics, irrespective of the choice of atomic species via which it is probed. Here, we show in the two-dimensional transition metal dichalcogenide semiconductor MoSe2, that through a selenium-based transition we observe charge carriers acting independently from each other, while when probed through molybdenum, the collective, many-body motion of the carriers dominates. Such unexpectedly contrasting behavior can be traced back to a strong localization of electrons around molybdenum atoms following absorption of light, which modifies the local fields acting on the carriers. We show that similar behavior in elemental titanium metal carries over to transition metal-containing compounds and is expected to play an essential role for a wide range of such materials. Knowledge of independent particle and collective response is essential for fully understanding these materials
Extra argumentality - affectees, landmarks, and voice
This article investigates sentences with additional core arguments of a special type in three languages, viz. German, English, and Mandarin. These additional arguments, called extra arguments in the article, form a crosslinguistically homogeneous class by virtue of their structural and semantic similarities, with so-called "raised possessors" forming just a sub-group among them. Structurally, extra arguments may not be the most deeply embedded arguments in a sentence. Semantically, their referents are felt to stand in a specific relation to the referent of the/a more deeply embedded argument. There are two major thematic relations that are instantiated by extra arguments, viz. affectees and landmarks. These thematic role notions are justified in the context of and partly in contrast to, Dowty's (1991) proto-role approach. An affectee combines proto-agent with proto-patient properties in eventualities that are construed as involving causation. A landmark is a ground with respect to some spatial configuration denoted by the predication at hand, but a figure at the highest level of gestalt partitioning that is relevant in a clause. Thereby, both affectees and landmarks are inherently hybrid categories. The account of extra argumentality is couched in a neo-Davidsonian event semantics in the spirit of Kratzer (1996, 2003), and voice heads are assumed to introduce affectee arguments and landmark arguments right above VP
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