Search

The generation of coherent light pulses in the extreme ultraviolet (XUV) spectral region with attosecond pulse durations constitutes the foundation of the field of attosecond science. Twenty years after the first demonstration of isolated attosecond pulses, they continue to be a unique tool enabling the observation and control of electron dynamics in atoms, molecules, and solids. It has long been identified that an increase in the repetition rate of attosecond light sources is necessary for many applications in atomic and molecular physics, surface science, and imaging. Although high harmonic generation (HHG) at repetition rates exceeding 100 kHz, showing a continuum in the cutoff region of the XUV spectrum, was already demonstrated in 2013, the number of photons per pulse was insufficient to perform pulse characterization via attosecond streaking, let alone to perform a pump-probe experiment. Here we report on the generation and full characterization of XUV attosecond pulses via HHG driven by near-single-cycle pulses at a repetition rate of 100 kHz. The high number of 10 6 XUV photons per pulse on target enables attosecond electron streaking experiments through which the XUV pulses are determined to consist of a dominant single attosecond pulse. These results open the door for attosecond pump-probe spectroscopy studies at a repetition rate 1 or 2 orders of magnitude above current implementations.

The generation of coherent light pulses in the extreme ultraviolet (XUV) spectral region with attosecond pulse durations constitutes the foundation of the field of attosecond science [1]. Twenty years after the first demonstration of isolated attosecond pulses [2], they continue to be a unique tool enabling the observation and control of electron dynamics in atoms, molecules and solids [3, 4]. It has long been identified that an increase in the repetition rate of attosecond light sources is necessary for many applications in atomic and molecular physics [5, 6], surface science [7], and imaging [8]. Although high harmonic generation (HHG) at repetition rates exceeding 100 kHz, showing a continuum in the cut-off region of the XUV spectrum was already demonstrated in 2013 [9], the number of photons per pulse was insufficient to perform pulse characterisation via attosecond streaking [10], let alone to perform a pump-probe experiment. Here we report on the generation and full characterisation of XUV attosecond pulses via HHG driven by near-single-cycle pulses at a repetition rate of 100 kHz. The high number of 106 XUV photons per pulse on target enables attosecond electron streaking experiments through which the XUV pulses are determined to consist of a dominant single attosecond pulse. These results open the door for attosecond pump-probe spectroscopy studies at a repetition rate one or two orders of magnitude above current implementations.

A high power optical parametric amplifier operating at 100 kHz repetition rate has been integrated into an attosecond pump-probe beamline. Attosecond pulses with high photon flux are generated and characterized in pump-probe experiments.

We report on the generation and characterization of trains and isolated attosecond pulses at a repetition rate of 100 kHz. This system will be utilized for attosecond pump-probe spectroscopy studies with electron-ion coincidence detection.

A high power, high repetition rate optical parametric chirped pulse amplification (OPCPA) system is presented. The OPCPA delivers Carrier-Envelope Phase (CEP)-stable 7 fs pulses, with up to 0.19mJ of energy, with a total compressed average power of 19 W. The system is being currently integrated in an attosecond pumpprobe beamline capable of combining attosecond pulses in the extreme ultraviolet (XUV) with synchronized few-cycle pulses in the near infrared (NIR). The main motivation for this development is to perform pump-probe experiments with attosecond time resolution, in which electrons and ions produced during photo-ionization are detected in coincidence utilizing a reaction microscope.

Many experiments in attosecond science will benefit from attosecond pulses at high repetition rates with sufficient photon flux for pump-probe experiments. We use 7fs, 800nm pulses from a non-collinear optical parametric chirped pulse amplification (NOPCPA) laser system to generate few-pulse attosecond pulse trains (APTs) in the extreme ultraviolet (XUV) at a repetition rate of 100kHz. The pulse trains have been fully characterized by recording FROG-CRAB (Frequency-Resolved Optical Gating for Complete Reconstruction of Attosecond Bursts) traces with a velocity map imaging spectrometer., Comment: 7 pages, 4 figures, submitted version

In laser-induced electron recollision, the returning wave packet retains structural information on its initial orbital., Electrons released by strong-field ionization from atoms and molecules or in solids can be accelerated in the oscillating laser field and driven back to their ion core. The ensuing interaction, phase-locked to the optical cycle, initiates the central processes underlying attosecond science. A common assumption assigns a single, well-defined return direction to the recolliding electron. We study laser-induced electron rescattering associated with two different ionization continua in the same, spatially aligned, polyatomic molecule. We show by experiment and theory that the electron return probability is molecular frame–dependent and carries structural information on the ionized orbital. The returning wave packet structure has to be accounted for in analyzing strong-field spectroscopy experiments that critically depend on the interaction of the laser-driven continuum electron, such as laser-induced electron diffraction.

It is shown that the effect of substrate heating on the photo conversion efficiency in vacuum-deposited small molecule organic solar cells is closely related to the improved free charge generation in ordered C60 regions. The formation of these ordered regions strongly depends on the deposition sequence in the device and differs therefore between inverted and noninverted cells. Substrate-induced local fullerene ordering is found in small molecule:C60 bulk heterojunctions (BHJs) deposited on pristine C60 at elevated temperatures. This does not occur for BHJs deposited under identical conditions on pristine donor molecule layers, despite similar degrees of phase separation in both cases. These findings point to a hitherto unidentified advantage of inverted over noninverted solar cells that manifests itself in a higher charge separation efficiency.

The progress in the development of a high acquisition rate attosecond XUV-IR pump-probe beamline is discussed. A high repetition rate parametric amplifier allows driving the harmonic generation process at a repetition rate of 100 kHz.

We study the Strong-Field Ionization (SFI) of the hydrocarbon 1-butene as a function of wavelength using photoion-photoelectron covariance and coincidence spectroscopy. We observe a striking transition in the fragment-associated photoelectron spectra: from a single Above Threshold Ionization (ATI) progression for photon energies less than the cation D0–D1 gap to two ATI progressions for a photon energy greater than this gap. For the first case, electronically excited cations are created by SFI populating the ground cationic state D0, followed by sequential post-ionization excitation. For the second case, direct sub-cycle SFI to the D1 excited cation state contributes significantly. Our experiments access ionization dynamics in a regime where strong-field and resonance-enhanced processes can interplay.

We report on the progress towards isolated attosecond pulses in the extreme ultraviolet at 100 kHz with high photon flux. The system will be used in pump-probe experiments detecting electrons and ions in coincidence.

Noncollinear optical parametric amplifiers (NOPAs) have become the leading technique for the amplification of carrier-envelope phase (CEP)-stable, few-cycle pulses at high repetition rate and high average power. In this Letter, a NOPA operating at a repetition rate of 100 kHz delivering more than 24 W of average power before compression is reported. The amplified bandwidth supports sub-7 fs pulse durations and pulse compression close to the transform limit is realized. CEP stability after amplification is demonstrated. The system paves the way to attosecond pump-probe spectroscopy with electron-ion coincidence detection.

Near single-cycle lasers have opened new frontiers in nonlinear optics and are essential tools for attosecond science [1]. In the last few years development in pulse characterization has been aimed both at improvements in fidelity and ease of use and also the ability to characterize ever shorter pulses down to near-single-or sub-cycle pulse durations [2, 3]. It is usually assumed that the electric field of a laser pulse can be factorized into a spatial and a temporal part E(x, y, t) = E(x, y) E(t). Most currently known and established pulse characterization techniques average over one or more spatial dimension of the beam or measure a sub-sample of the beam selected by an aperture, which can lead to errorneous measurements even in case of benign sources like hollow fiber compressors due to the inherent radially varying spectrum in the collimated beam. For most experiments space-time couplings are detrimental but for some e.g. the attosecond gating scheme by ultrafast wavefront rotation, the introduction of deliberate space-time couplings where E(x, y, t) ≠ E(x, y) E(t) is desirable [4].

Synopsis An attosecond pump-probe beamline with 100 kHz repetition rate for coincidence experiments has been developed. It is based on non-collinear optical parametric chirped pulse amplification and delivers 100 μJ sub-4 fs to an high-harmonic generation source. Details on the generation and characterization of isolated attosecond pulses will be presented.

A noncollinear optical parametric amplifier delivering more than 23 W at 100 kHz at a central wavelength of 850 nm is presented. After compression pulses of 7.2 fs with more than 210 μJ are obtained.

Strong field ionization of small hydrocarbon chains is studied in a kinematic complete experiment using a reaction microscope. By coincidence detection of ions and electrons different ionization continua populated during the ionization process are identified. In addition, photoelectron momentum distributions from laser-aligned molecules allow to characterize the electron wavepackets emerging from different Dyson orbitals.