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Explicit visualization of different components of surface plasmon polaritons (SPPs) propagating at dielectric/metal interfaces is crucial in offering chances for the detailed design and control of the functionalities of plasmonic nanodevices in the future. Here, we reported independent imaging of the vertical and horizontal components of SPPs launched from a rectangular trench in the gold film by a 400-nm laser-assisted near-infrared (NIR) femtosecond laser time-resolved photoemission electron microscopy (TR-PEEM). The experiments demonstrate that distinct imaging of different components of SPPs field can be easily achieved by introducing the 400-nm laser. It can circumvent the risk of sample damage and information loss of excited SPPs field that is generally confronted in the usual NIR laser TR-PEEM scheme. The underlying mechanism for realizing distinct imaging of different components of the SPPs field with two-color PEEM is revealed via measuring the double logarithmic dependence of photoemission yield with the 800-nm and 400-nm pulse powers of different polarizations. Moreover, it is found that the PEEM image quality of the vertical and horizontal components of the SPPs field is nearly independent of the 400-nm pulse polarization. These results pave a way for SPPs-based applications and offer a possible solution for drawing a spaceâ€"time field of SPPs in three dimensions. [ABSTRACT FROM AUTHOR]

We show that generation of strong magnetic field filaments due to Weibel instability accompanies the hole-boring ion acceleration by a circularly polarised laser pulse. The magnetic field confines energetic protons accelerated from hole boring in high density collimated jets. A part of energetic protons are reaccelerated by the electric field and focused by the magnetic field generated from the jets. As a result, highly collimated proton jets with high cutoff energy can be produced. [ABSTRACT FROM AUTHOR]

The reconnection rate in relativistic magnetic reconnection driven by two relativistic intense femtosecond laser pulses is investigated using three-dimensional particle-in-cell (PIC) simulation. As the drive is enhanced, the current sheet is narrowed, and the reconnection rate is weakened. A new theoretical model is given to explain the rate observed in the PIC simulation. In addition, multi-scale reconnection is studied by setting a different ion mass in the simulation code. For , the current sheet is only at the electron scale, and only electron outflow jets are observed, which are super ion Alfvénic and close to the electron's Alfvénic speed. The lengths of the electron outflow jets reach 100–200 times the length of the electron gyroradius and beyond the ion gyroradius. However, when , more ions are coupled to electrons during the laser and plasma interaction, there are also electron outflow jets and no ion outflow jets in the current sheet, and the electron outflow jets are embedded in a wider ion-scale current layer. [ABSTRACT FROM AUTHOR]

As a femtosecond terawatt laser pulse propagates along a positive density gradient within a stratified plasma column, it drives a low-frequency electromagnetic wake wave, the period of electron fluid oscillations in the wake gradually shrinking. Phase velocity of the wake promptly exceeds the vacuum speed of light, setting in near-forward emission of terahertz Cherenkov radiation. As the wake accelerates further, the Cherenkov emission ray rotates by 180∘. Emission from a given plasma locality is sustained for a finite interval of time, in the middle of which the wake experiences a 'reversal,' its phase velocity becoming singular and changing sign (Zhang C J et al 2017 Phys. Rev. Lett. 119 064801) At this instant, the electromagnetic energy flows at 90∘, the emission power reaching its peak. After the reversal, the wake keeps radiating into the rear hemisphere until its phase velocity becomes subluminal. Experimentally capturing evolution of the Cherenkov signal may thus shed light onto the plasma wake dynamics. Far away from the plasma, the radiation fills an expanding, almost spherical shell, the shell thickness increasing with an increase in the observation angle. The length of the terahertz signal sampled in the wave zone thus ranges from zero (forward emission) to a few tens of picoseconds (backward emission). The signal is positively chirped, its frequency increasing from the Langmuir frequency at the foot of the column to the Langmuir frequency at the top. Theoretical estimates for the regimes involving 10 TW-class drive pulses promise a few-kW emission power; the energy conversion efficiency, from optical to terahertz, of order 10−7; and an MV m−1-scale electric field strength centimeters away from the plasma. [ABSTRACT FROM AUTHOR]

We study the influence of the polarization states of ionizing femtosecond two-color pulses on the emitted terahertz radiation in gases. A local-current model and plane-wave evaluations justify the previously-reported impact on the THz energy yield and a (almost) linearly-polarized THz field when using circularly-polarized laser harmonics. For such pump pulses, the THz yield is independent of the relative phase between the two colors. When the pump pulses have same helicity, the increase in the THz yield is associated with longer ionization sequences and higher electron transverse momenta acquired in the driving field. Reversely, for two color pulses with opposite helicity, the dramatic loss of THz power comes from destructive interferences driven by the highly symmetric response of the photocurrents lined up on the third harmonic of the fundamental pulse. While our experiments confirm an increased THz yield for circularly-polarized pumps of same helicity, surprisingly, the emitted THz radiation is not linearly-polarized. This effect is explained by means of comprehensive 3D numerical simulations highlighting the role of the spatial alignment and non-collinear propagation of the two colors. [ABSTRACT FROM AUTHOR]