Direct characterisation of tuneable few-femtosecond dispersive-wave pulses in the deep UV

Dispersive wave emission (DWE) in gas-filled hollow-core dielectric waveguides is a promising source of tuneable coherent and broadband radiation, but so far the generation of few-femtosecond pulses using this technique has not been demonstrated. Using in-vacuum frequency-resolved optical gating, we directly characterise tuneable 3fs pulses in the deep ultraviolet generated via DWE. Through numerical simulations, we identify that the use of a pressure gradient in the waveguide is critical for the generation of short pulses.Comment: 5 pages, 4 figure

Prospects for photon blockade in four level systems in the N configuration with more than one atom

We show that for appropriate choices of parameters it is possible to achieve photon blockade in idealised one, two and three atom systems. We also include realistic parameter ranges for rubidium as the atomic species. Our results circumvent the doubts cast by recent discussion in the literature (Grangier et al Phys. Rev Lett. 81, 2833 (1998), Imamoglu et al Phys. Rev. Lett. 81, 2836 (1998)) on the possibility of photon blockade in multi-atom systems.Comment: 8 page, revtex, 7 figures, gif. Submitted to Journal of Optics B: Quantum and Semiclassical Optic

Strong-field ionization of clusters using two-cycle pulses at 1.8 μm

The interaction of intense laser pulses with nanoscale particles leads to the production of high-energy electrons, ions, neutral atoms, neutrons and photons. Up to now, investigations have focused on near-infrared to X-ray laser pulses consisting of many optical cycles. Here we study strong-field ionization of rare-gas clusters (103 to 105 atoms) using two-cycle 1.8 μm laser pulses to access a new interaction regime in the limit where the electron dynamics are dominated by the laser field and the cluster atoms do not have time to move significantly. The emission of fast electrons with kinetic energies exceeding 3 keV is observed using laser pulses with a wavelength of 1.8 μm and an intensity of 1 × 1015 W/cm2, whereas only electrons below 500 eV are observed at 800 nm using a similar intensity and pulse duration. Fast electrons are preferentially emitted along the laser polarization direction, showing that they are driven out from the cluster by the laser field. In addition to direct electron emission, an electron rescattering plateau is observed. Scaling to even longer wavelengths is expected to result in a highly directional current of energetic electrons on a few-femtosecond timescale

Low-Energy Electron Emission in the Strong-Field Ionization of Rare Gas Clusters

Clusters and nanoparticles have been widely investigated to determine how plasmonic near fields influence the strong-field induced energetic electron emission from finite systems. We focus on the contrary, i.e., the slow electrons, and discuss a hitherto unidentified low-energy structure (LES) in the photoemission spectra of rare gas clusters in intense near-infrared laser pulses. For Ar and Kr clusters we find, besides field-driven fast electrons, a robust and nearly isotropic emission of electrons with <4  eV kinetic energies that dominates the total yield. Molecular dynamics simulations reveal a correlated few-body decay process involving quasifree electrons and multiply excited ions in the nonequilibrium nanoplasma that results in a dominant LES feature. Our results indicate that the LES emission occurs after significant nanoplasma expansion, and that it is a generic phenomenon in intense laser nanoparticle interactions, which is likely to influence the formation of highly charged ions

Electronic Quantum Coherence in Glycine Molecules Probed with Ultrashort X-ray Pulses in Real Time

Structural changes in nature and technology are driven by charge carrier motion. A process such as charge-directed reactivity that can be operational in radiobiology is more efficient, if energy transfer and charge motion proceeds along well-defined quantum mechanical pathways keeping the coherence and minimizing dissipation. The open question is: do long-lived electronic quantum coherences exist in complex molecules? Here, we use x-rays to create and monitor electronic wave packets in the amino acid glycine. The outgoing photoelectron wave leaves behind a positive charge formed by a superposition of quantum mechanical eigenstates. Delayed x-ray pulses track the induced electronic coherence through the photoelectron emission from the sequential double photoionization processes. The observed sinusoidal modulation of the detected electron yield as a function of time clearly demonstrates that electronic quantum coherence is preserved for at least 25 femtoseconds in this molecule of biological relevance. The surviving coherence is detected via the dominant sequential double ionization channel, which is found to exhibit a phase shift as a function of the photoelectron energy. The experimental results agree with advanced ab-initio simulations.Comment: 54 pages, 11 figure

Ultrafast X-ray Science: Measuring the very fast and the very small

Madrid, Edificio central CSIC, 11 octubre 2019. -- ColoquioCurie.csic.esEn esta ocasión el Dr. Jon Marangos, del Imperial College (Londres), presentará la charla: ¿Ultrafast X-ray Science: Measuring the very fast and the very small¿