Jon: LCLS briefing + Zara: JC: Quasi-phase-matching-induced enhancement of high-order harmonics during two-colour pump of multi-jet plasmas

Jon: LCLS: probing hole dynamics in glycine 



Zara: Quasi-phase-matching-induced enhancement of high-order harmonics during two-colour pump of multi-jet plasmas

The first demonstration of quasi-phase-matching during high-order harmonic generation (HHG) of laser radiation in multi-jet plasmas produced on the silver and chromium targets under the conditions of two-colour pump (804 and 402 nm) is presented. We analyse the enhancement of the groups of odd and even harmonics along the plateau range and compare the harmonic yields using a different number of plasma jets. The comparison of extended line plasma and multi-jet plasma shows the advanced properties of the latter formation for the efficient HHG using the two-colour pump. The 25× and 13× enhancement factors of quasi-phase-matched harmonics were obtained in the cases of the two-colour and single-colour pumps of multi-jet plasmas.

http://iopscience.iop.org/0953-4075/47/10/105401

http://iopscience.iop.org/0953-4075/47/10/105401/pdf/0953-4075_47_10_105401.pdf

Davide: JC: Coherent phase-matched VUV generation by field-controlled bound states

The generation of high-order harmonics1 and attosecond pulses2 at ultrahigh repetition rates (>1 MHz) promises to revolutionize ultrafast spectroscopy. Such vacuum ultraviolet (VUV) and soft X-ray sources could potentially be driven directly by plasmonic enhancement of laser pulses from a femtosecond oscillator3, 4, but recent experiments suggest that the VUV signal is actually dominated by incoherent atomic line emission5, 6. Here, we demonstrate a new regime of phase-matched below-threshold harmonic generation, for which the generation and phase matching is enabled only near resonance structures of the atomic target. The coherent VUV line emission exhibits low divergence and quadratic growth with increasing target density up to nearly 1,000 torr mm and can be controlled by the sub-cycle field of a few-cycle driving laser with an intensity of only ~1 × 1013 W cm−2, which is achievable directly from few-cycle femtosecond oscillators with nanojoule energy7.

http://www.nature.com/nphoton/journal/vaop/ncurrent/full/nphoton.2014.83.html

Nick: JC: Frequency domain optical parametric amplification

Today’s ultrafast lasers operate at the physical limits of optical materials to reach extreme performances. Amplification of single-cycle laser pulses with their corresponding octave-spanning spectra still remains a formidable challenge since the universal dilemma of gain narrowing sets limits for both real level pumped amplifiers as well as parametric amplifiers. We demonstrate that employing parametric amplification in the frequency domain rather than in time domain opens up new design opportunities for ultrafast laser science, with the potential to generate single-cycle multi-terawatt pulses. Fundamental restrictions arising from phase mismatch and damage threshold of nonlinear laser crystals are not only circumvented but also exploited to produce a synergy between increased seed spectrum and increased pump energy. This concept was successfully demonstrated by generating carrier envelope phase stable, 1.43?mJ two-cycle pulses at 1.8?µm wavelength.

http://www.nature.com/ncomms/2014/140507/ncomms4643/full/ncomms4643.html#ref-link-38

Malte: DM: Phase characterisation of plasmons

The field of plasmonics promises a brave new world of microprocessing, sensing and low-power nonlinear optics. Existing approaches to measuring plasmon fields using streaking are very involved, so an all-optical method to catch a glimpse of the surface dynamics is highly desirable. I carried out spectral interferometry on the reflected residual pump beam used to excite surface plasmon polaritons on a diffraction grating in order to characterise the phase of the propagating plasmon. I furthermore simulated the experimental situation using FDTD methods to connect the far-field results to the surface fields. Initial results show qualitative agreement between experiment and simulation, with the latter most likely critically limited by computational resources. As such, the progress so far demonstrates that the technique can indeed yield information about the plasmon dynamics in the far field with comparatively little experimental effort.

Will: JC: In situ measurement of nonlinear carrier-envelope phase changes in hollow fiber compression

We demonstrate a simple and robust single-shot interferometric technique that allows the in situ measurement of intensity-dependent phase changes experienced by ultrashort laser pulses upon nonlinear propagation. The technique is applied to the characterization of carrier-envelope phase noise in hollow fiber compressors both in the pressure gradient and in the static cell configuration. Measurements performed simultaneously with conventional f-to-2f interferometers before and after compression indicate that the noise emerging in the waveguide adds up arithmetically to the phase noise of the amplifier, thus being strongly correlated to the phase noise of the pulses coupled into the compressor.

http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-39-8-2302

Zsolt: JC: How to focus an attosecond pulse

Attosecond experiments involving focusing of attosecond light pulses can suffer from a spread of the attosecond radiation both in space and time due to optical aberrations. We present a detailed numerical study of the distortions induced in the most common focusing geometries that make use of parabolic, spherical, toroidal and ellipsoidal mirrors. We deduce the consequences on the pulse duration and possible issues that could arise in applications of attosecond pulses. This should serve as a guideline for setting up attosecond focusing optics.

http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-21-2-2506

Zolt: JC: Laser dressed absorption studies

Two papers will serve the bases:

Lucchini et al. Role of electron wavepacket interference in the optical response of helium atoms, NJP, 15, (2013)
Gallmann et al. Resolving intra-atomic electron dynamics with attosecond transient absorption spectroscopy, Molecular Physics, 111, (2013)