At high intensities, light-matter interactions are controlled by the electric field of the exciting light. For instance, when an intense laser pulse interacts with an atomic gas, individual cycles of the incident electric field ionize gas atoms and steer the resulting attosecond-duration electrical wavepackets 1,2 . Such field-controlled light-matter interactions form the basis of attosecond science and have recently expanded from gases to solid-state nanostructures [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] . Here, we extend these field-controlled interactions to metallic nanoparticles supporting localized surface plasmon resonances. We demonstrate strong-field, carrier-envelope-phase-sensitive photoemission from arrays of tailored metallic nanoparticles, and we show the influence of the nanoparticle geometry and the plasmon resonance on the phase-sensitive response. Additionally, from a technological standpoint, we push strong-field light-matter interactions to the chip scale. We integrate our plasmonic nanoparticles and experimental geometry in compact, microoptoelectronic devices that operate out of vacuum and under ambient conditions.Moving from low to high optical intensity, photoemission goes from photon-driven to field-controlled. Consider illuminating a metallic surface with an infrared femtosecond laser pulse with electric field F(t) = F 0 A(t) cos(ωt + ϕ), where F 0 is the peak field, A(t) is the normalized pulse envelope, ω is the carrier frequency, and ϕ is the carrier-envelope phase (CEP). When the pulse interacts with the metallic surface, electrons are excited out of the metal and into the surrounding vacuum. At typical incident intensities, this photoemission process is photon-driven: emission is dictated by the pulse's photon energy, that is, ω, and photon flux, that is, the pulse's intensity envelope ∝ |F 0 A(t)| 2 . At high intensities, this photoemission process resembles field-controlled tunnelling. The strong electric field of the pulse deflects the binding potential of the metallic surface and drives electron tunnelling through the distorted barrier. This tunnelling occurs over a timescale τ t = √ 2mW F /eF 0 , where W F is the workfunction of the surface, m is the electron mass, and e is its charge 19,20 . With sufficiently strong F 0 , τ t becomes shorter than the characteristic cycle time of the exciting laser light (τ t < τ cyc = 1/ω), and individual cycles of the driving electric field eject subcycle electrical bursts from the metal and steer these ultrafast currents through the surrounding vacuum 6,8 ; in this strongfield regime, photoemission is controlled by the driving optical electric field and, accordingly, by the CEP, ϕ.In recent years, metallic nanotips have emerged as platforms to non-destructively investigate photoemission in the strong-field regime. When a nanotip is illuminated by a femtosecond laser pulse, the incident field is locally enhanced at the apex of the tip. Due primarily to the tip's sharp geometry, the field enhancement is typically <10, and th...

Femtosecond ultrabright electron sources with spatially structured emission are an enabling technology for free-electron lasers, compact coherent X-ray sources, electron diffractive imaging, and attosecond science. In this work, we report the design, modeling, fabrication, and experimental characterization of a novel ultrafast optical field emission cathode comprised of a large (>100,000 tips), dense (4.6 million tips·cm(-2)), and highly uniform (<1 nm tip radius deviation) array of nanosharp high-aspect-ratio silicon columns. Such field emitters offer an attractive alternative to UV photocathodes while providing a direct means of structuring the emitted electron beam. Detailed measurements and simulations show pC electron bunches can be generated in the multiphoton and tunneling regime within a single optical cycle, enabling significant advances in electron diffractive imaging and coherent X-ray sources on a subfemtosecond time scale, not possible before. At high charge emission yields, a slow rollover in charge is explained as a combination of the onset of tunneling emission and the formation of a virtual cathode.

Here we demonstrate the design, fabrication, and characterization of ultrafast, surface-plasmon enhanced Au nanorod optical field emitter arrays. We present a quantitative study of electron emission from Au nanorod arrays fabricated by high-resolution electron-beam lithography and excited by 35 fs pulses of 800 nm light. We present accurate models for both the optical field enhancement of Au nanorods within high-density arrays, and electron emission from those nanorods. We have also studied the effects of surface plasmon damping induced by metallic interface layers at the substrate/nanorod interface on near-field enhancement and electron emission. We have identified the peak optical field at which the electron emission mechanism transitions from a 3-photon absorption mechanism to strong-field tunneling emission. Moreover, we have investigated the effects of nanorod array density on nanorod charge yield, including measurement of space-charge effects. The Au nanorod photocathodes presented in this work display 100-1000 times higher conversion efficiency relative to previously reported UV triggered emission from planar Au photocathodes. Consequently, the Au nanorod arrays triggered by ultrafast pulses of 800 nm light in this work may outperform equivalent UV-triggered Au photocathodes, while also offering nanostructuring of the electron pulse produced from such a cathode, which is of interest for X-ray free-electron laser (XFEL) development where nanostructured electron pulses may facilitate more efficient and brighter XFEL radiation.

Extracting light from silicon is a longstanding challenge in modern engineering and physics. While silicon has underpinned the past 70 years of electronics advancement, a facile tunable and efficient silicon-based light source remains elusive. Here, we experimentally demonstrate the generation of tunable radiation from a one-dimensional, all-silicon nanograting. Light is generated by the spontaneous emission from the interaction of these nanogratings with low-energy free electrons (2–20 keV) and is recorded in the wavelength range of 800–1600 nm, which includes the silicon transparency window. Tunable free-electron-based light generation from nanoscale silicon gratings with efficiencies approaching those from metallic gratings is demonstrated. We theoretically investigate the feasibility of a scalable, compact, all-silicon tunable light source comprised of a silicon Field Emitter Array integrated with a silicon nanograting that emits at telecommunication wavelengths. Our results reveal the prospects of a CMOS-compatible electrically-pumped silicon light source for possible applications in the mid-infrared and telecommunication wavelengths.

Ultrafast, high-intensity light-matter interactions lead to optical-field-driven photocurrents with an attosecond-level temporal response. These photocurrents can be used to detect the carrier-envelope-phase (CEP) of short optical pulses, and enable optical-frequency, petahertz (PHz) electronics for high-speed information processing. Despite recent reports on opticalfield-driven photocurrents in various nanoscale solid-state materials, little has been done in examining the large-scale electronic integration of these devices to improve their functionality and compactness. In this work, we demonstrate enhanced, on-chip CEP detection via optical-field-driven photocurrents in a monolithic array of electrically-connected plasmonic bow-tie nanoantennas that are contained within an area of hundreds of square microns. The technique is scalable and could potentially be used for shot-to-shot CEP tagging applications requiring orders-of-magnitude less pulse energy compared to alternative ionization-based techniques. Our results open avenues for compact time-domain, on-chip CEP detection, and inform the development of integrated circuits for PHz electronics as well as integrated platforms for attosecond and strong-field science.