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The sub-cycle interaction of light and matter is one of the key frontiers of inquiry made accessible by attosecond science. Here, we show that when light excites a pair of charge carriers inside of a solid, the transition probability is strongly localized to instants slightly after the extrema of the electric field. The extreme temporal localization is utilized in a simple electronic circuit to record the waveforms of infrared to ultraviolet light fields. This form of petahertz-bandwidth field metrology gives access to both the modulated transition probability and its temporal offset from the laser field, providing sub-fs temporal precision in reconstructing the sub-cycle electronic response of a solid state structure.

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A new class of bowtie antennas with Sierpiński fractal features is proposed for sensing molecular vibration modes in the near- to mid-infrared. These antennas offer a compact device footprint and an enhanced confinement factor compared to a bowtie antenna. Through extensive simulations, it is shown that these characteristics are related to the ability of this fractal geometry to become polarized. Simulation results demonstrate that these antennas may be tuned between 700 nm ≤ λ ≤ 3.4 µm and that electric field enhancement by 56 is possible at the center of the antenna gap.

Measuring the magnetic response of matter relies acutely on the degree to which a magnetic field source's amplitude, spatial, and temporal character can be tailored. Magnetic fields are inseparable from light-matter interaction, yet due to the dominance of electric-field-induced effects in many systems, laser pulses have heretofore provided comparatively limited insight into the high-frequency magnetic response of matter. Conductors or superconductors arranged in a solenoidal configuration embody the state-ofthe-art apparatus for generating spatially isolated magnetic fields, but the reliance on electrical circuitry limits the field amplitude, pulse brevity, and absolute timing of the generated fields. We transfer the concept of solenoidal currents commonly leveraged in electromagnets to photo-ionized electrons driven by moderately intense vector laser beams, in a scheme that does not require the laser mode to carry orbital angular momentum. We predict that this all-optical approach will enable magnetic fields exceeding 8 Tesla to be turned on within 50 femtoseconds using moderate laser intensities, an unprecedented combination of parameters that will open the possibility for ultrafast metrological techniques to be combined with intense, spatially isolated, magnetic fields.Magnetic fields play a fundamental role in our understanding of magnetic materials [1], electron spins [2,3], superconductivity [4][5][6], quantum and topological systems [7-9], plasma and nuclear fusion [10-12], medical diagnosis [13], and astrophysics [14]. Electric charge in motion generates magnetic fields [15,16], and the arrangement of conductors or superconductors into loops or solenoids has been the workhorse approach to magnetic field sources for decades. Although effective for measuring the quasistatic magnetic response of matter, the ultrafast dynamics that ultimately produces this response remains largely inaccessible.As an alternative, relativistic electron bunches have been used to introduce a strong magnetic pulse of 2.3 ps duration to a granular recording film [17]. The application of large magnetic fields of short duration enables insight into the maximum switching bandwidth of the magnetic material before the onset of magnetic disorder. Although these results provide intriguing fundamental insight with important technological implications, the large-scale electron acceleration facility required for these measurements limits the exploration of ultrafast dynamics in other material systems.Extensive effort has been devoted to optically exciting solenoidal currents and high magnetic fields in underdense plasmas using relativistic laser pulses, for the purpose of charged beam collimation. Early approaches were based on the inverse Faraday effect [18], whereby the angular momentum is transferred from a circularly polarized beam to the plasma via dissipative effects. The recent availability of optical vortex beams [i.e., laser modes that carry orbital angular momentum (OAM)] at relativistic intensities [19] has motivated new approach...

A plasmonic antenna design is proposed and investigated numerically over a large parameter space. By considering the contour of a bowtie antenna and introducing an additional design parameter, the contour thickness, it is demonstrated that the resonant wavelength of the antenna may be tuned over a broad spectral range while maintaining a constant antenna footprint. These new antennas allow for a factor of 3.6 reduction in the antenna footprint and an increase in the gap enhancement by 28%.

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We report visible third-harmonic conversion at λ=517 nm in subwavelength silicon-based nanoplasmonic waveguides at an unprecedented conversion efficiency of 2.3×10^{-5}. This marks both the highest third-harmonic conversion efficiency in a silicon-based or nanoplasmonic structure and the smallest silicon waveguide structure demonstrated to date. The high conversion efficiency is attributed to tight electric field confinement and strong light-matter coupling arising from surface plasmon modes in the nanoplasmonic waveguide, enabling efficient nonlinear optical mixing over micrometer length scales. The nonresonant geometry of the waveguide enables the entire λ=1550 nm femtosecond pulse spectrum to be converted to its third harmonic, which may be easily extended to the entire visible spectrum. We envisage that third-harmonic generation in silicon-based nanoplasmonic waveguides could provide a platform for integrated, broadband visible light sources and entangled triplet photons on future hybrid electronic-silicon photonic chips.