Harmonic generation by atomic and nanoparticle precursors in a ZnS laser ablation plasma

Harmonic generation of a driving laser propagating across a laser ablation plasma serves for the diagnosis of multicomponent plumes. Here we study the contribution of atomic and nanoparticle precursors to the generation of coherent ultraviolet and vacuum ultraviolet light as low-order harmonics of the fundamental emission (1064 nm) of a Q-switched Nd:YAG laser in a nanosecond infrared ZnS laser ablation plasma. Odd harmonics from the 3rd up to the 9th order (118.2 nm) have been observed with distinct temporal and spatial characteristics which were determined by varying the delay between the ablation and driving nanosecond pulses and by spatially scanning the plasma with the focused driving beam propagating parallel to the target. At short distances from the target surface (≤1 mm), the harmonic intensity displays two temporal components peaked at around 250 ns and 10 μs. While the early component dies off quickly with increasing harmonic order and vanishes for the 9th order, the late component is notably intense for the 7th harmonic and is still clearly visible for the 9th. Spectral analysis of spontaneous plume emissions help to assign the origin of the two components. While the early plasma component is mainly constituted by neutral Zn atoms, the late component is mostly due to nanoparticles, which upon interaction with the driving laser are subject to breakup and ionization. With the aid of calculations of the phase matching integrals within the perturbative model of optical harmonic generation, these results illustrate how atom and nanoparticle populations, with differing temporal and spatial distributions within the ablation plasma, contribute to the nonlinear medium.Funding has been provided by Ministerio de Economía y Competitividad (MINECO) of Spain under Project CTQ2013-43086-P. I.L-Q., A.B-C. and M.O. thank respectively MINECO, for a FPI fellowship (BES-2011-044738), CSIC, for a JAE-TEC 2010 contract and CSIC for a contract. Fruitful discussions with Dr. Mikel Sanz and Prof. A. Gonzalez-Arroyo are acknowledged.Peer reviewe

Low-order harmonic generation in a ZnS laser ablation plasma

Low-order (3rd to 9th) harmonic generation of a near-infrared driving laser (1064 nm) is reported in a laser ablation plasma of ZnS. Temporal analysis shows two distinct components with respect to the ablation event. The late temporal component exhibits high conversion efficiency for the highest harmonic orders observed. This is attributed to a dramatic modification of the plasma medium with the driving laser.Peer Reviewe

Optical vortex production mediated by azimuthal index of radial polarization

[EN]Special light beams are becoming more and more interesting due to their applications in particle manipulation, micromachining, telecommunications or light matter-interaction. Both spin and orbital angular momenta of light are exploited often in combination with spatially varying linear polarization profiles (e.g. radial or azimuthal distributions). In this work we study the interaction between those polarization profiles and the spin-orbit angular momenta, finding the relation involved in the mode coupling. We find that this manipulation can be used for in-line production of collinear optical vortices with different topological charges, which can be filtered or combined with controlled linear polarization. The results are valid for continuous wave and ultrashort pulses, as well as for collimated and focused beams. We theoretically demonstrate the proposal, which is further confirmed with numerical simulations and experimental measurements with ultrashort laser pulses.This work was partially funded by Junta de Castilla y León (SA287P18) and FEDER Funds; Spanish Ministerio de Economía y Competitividad (MINECO) (FIS2017-87970-R, EQC2018-004117-P); European Research Council (ENIGMA)

Faster chiral versus collinear magnetic order recovery after optical excitation revealed by femtosecond XUV scattering

While chiral spin structures stabilized by Dzyaloshinskii-Moriya interaction (DMI) are candidates as novel information carriers, their dynamics on the fs-ps timescale is little known. Since with the bulk Heisenberg exchange and the interfacial DMI two distinct exchange mechanisms are at play, the ultra-fast dynamics of the chiral order needs to be ascertained and compared to the dynamics of the conventional collinear order. Using an XUV free-electron laser we determine the fs-ps temporal evolution of the chiral order in domain walls in a magnetic thin film sample by an IR pump - X-ray magnetic scattering probe experiment. Upon demagnetisation we observe that the dichroic (CL-CR) signal connected with the chiral order correlator $m_z m_x$ in the domain walls recovers significantly faster than the (CL+CR) sum signal representing the average collinear domain magnetisation $m_z^2 + m_x^2$. We explore possible explanations based on spin structure dynamics and reduced transversal magnetisation fluctuations inside the domain walls and find that the latter can explain the experimental data leading to different dynamics for collinear magnetic order and chiral magnetic order.Comment: 28 pages, 14 figure

Femtosecond double-pulse laser ablation and deposition of Co-doped ZnS thin films

Nanostructured thin films of Co-doped zinc sulfide were synthesized through femtosecond pulsed laser deposition. The scheme involved ablation of physically mixed Co and ZnS with pairs of ultrashort pulses separated in time in the 0-300 ps range. In situ monitorization of the deposition process was carried out through a simultaneous reflectivity measurement. The crystallinity of generated nanoparticles and the inclusion of Co in the ZnS lattice is demonstrated by transmission electron microscopy and energy dispersive X-ray microanalysis (TEM-EDX) characterization. Surface morphology, Raman response, and photoluminescence of the films have also been assessed. The role of interpulse temporal separation is most visible in the thickness of the films obtained at the same total fluence, with much thicker films deposited with short delays than with individual uncoupled pulses. The proportion of Co in the synthesized doped ZnS nanoparticles is found to be substantially lower than the original proportion, and practically independent on interpulse delay

Author correction: femtosecond laser mass spectrometry and high harmonic spectroscopy of xylene isomers

1 pags. -- Correction to: Scientific Reports https://doi.org/10.1038/s41598-018-22055-9, published online 28 February 2018A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.Peer reviewe

Nueva metodología y recursos online para la adaptación de las prácticas de laboratorio de Óptica a escenarios docentes con diferente grado de presencialidad

Memoria ID-040 Ayudas de la Universidad de Salamanca para la innovación docente, curso 2020-2021

Ultrafast opto-magnetic effects in the extreme ultraviolet spectral range

Coherent light-matter interactions mediated by opto-magnetic phenomena like the inverse Faraday effect (IFE) are expected to provide a non-thermal pathway for ultrafast manipulation of magnetism on timescales as short as the excitation pulse itself. As the IFE scales with the spin-orbit coupling strength of the involved electronic states, photo-exciting the strongly spin-orbit coupled core-level electrons in magnetic materials appears as an appealing method to transiently generate large opto-magnetic moments. Here, we investigate this scenario in a ferrimagnetic GdFeCo alloy by using intense and circularly polarized pulses of extreme ultraviolet radiation. Our results reveal ultrafast and strong helicity-dependent magnetic effects which are in line with the characteristic fingerprints of an IFE, corroborated by ab initio opto-magnetic IFE theory and atomistic spin dynamics simulations

Roadmap on spatiotemporal light fields

Spatiotemporal sculpturing of light pulse with ultimately sophisticated structures represents the holy grail of the human everlasting pursue of ultrafast information transmission and processing as well as ultra-intense energy concentration and extraction. It also holds the key to unlock new extraordinary fundamental physical effects. Traditionally, spatiotemporal light pulses are always treated as spatiotemporally separable wave packet as solution of the Maxwell's equations. In the past decade, however, more generalized forms of spatiotemporally nonseparable solution started to emerge with growing importance for their striking physical effects. This roadmap intends to highlight the recent advances in the creation and control of increasingly complex spatiotemporally sculptured pulses, from spatiotemporally separable to complex nonseparable states, with diverse geometric and topological structures, presenting a bird's eye viewpoint on the zoology of spatiotemporal light fields and the outlook of future trends and open challenges.Comment: This is the version of the article before peer review or editing, as submitted by an author to Journal of Optics. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from i