The third movement of Tchaikovsky's Symphony No. 4 consists almost entirely of the string section playing pizzicato – short plucks of the string – in precisely-timed running eighth notes. In their article on Strong-Field Photoemission From Silicon Field Emitter Arrays, Keathley et al.1 demonstrate a similar situation: the orchestra is now a nanoscale array of sharp tips emitting electrons in synchrony, thanks to the conductor – a laser keeping time at the frantic tempo of 1 kHz using pulses of light lasting only 35 fs. And perhaps as in a world-class orchestra, every member of this array is a semiconductor, which has practical benefits (discussed below) that should make arrays of silicon tips attractive candidates for ultrafast pulsed electron sources. Field emission tips triggered by ultrafast laser pulses have been under increasingly extensive investigation over the last several years, owing to several attractive properties as electron sources. First, the sub-optical-wavelength size of the emitters gives rise to enhancement of the laser field, which combined with their low work function (several eV) has allowed strong-field emission (optical field emission) to be observed in both tungsten and gold 2, 3 for significantly lower laser intensity than in noble gases. For instance, in 4 the pulse train of a typical Ti:Sapphire femtosecond laser operating at 80-MHz repetition frequency was able to drive sharp tungsten tips into the strong-field regime. For tunneling emission in DC, sharp tips provide a localized electron source with high brightness and a narrow energy spread. Such a beam is a prerequisite for pulsed experiments where signal size is at a premium and complex electron optics require low energy spread. When the tunneling emission is instead caused by the oscillating electric field of light at the surface of the emitter, electron wavepackets with durations lasting less than the period of an optical cycle are born. Until very recently, only single tips made of metal were studied under illumination with fs pulsed light. Sub-cycle timing control of field emission 4, control of the emission site 5, and an understanding of thermal effects 6 have all been achieved in such systems. However, the total per-pulse charge extracted from single tips is limited to below ∼1000 electrons due to the small emission area which is typically a few nm in size. Mustonen et al. have recently shown that large amounts of charge (several pC per pulse) can be extracted from a cathode fabricated as an array of very sharp molybdenum tips 7. Combining the emission from every tip, the total charge is in an interesting regime for applications such as high-flux x-ray generation, accelerator applications such as free-electron lasers, and vacuum electronic amplifiers and oscillators. An exciting and challenging proposal to create microbunched pulses for coherent x-ray generation was also recently described by Graves et al., wherein the transverse structure of emission from such an array of tips is converted into a longitudinal structure via a complex yet compact (just over 2-m long) accelerator structure 8. The structure generates periodic bunching of the electrons at the desired x-ray wavelength, allowing in-phase creation of x-rays via inverse Compton scattering. It is precisely this application – an efficient, compact, advanced x-ray source – that serves as a significant motivation for the work of Keathley et al. Instead of an array of metallic tips, however, an array of heavily n-doped silicon tips is investigated. Use of silicon has advantages such as scalability and uniformity of tip fabrication, as well as relaxed vacuum requirements for emission. Also, 1 serves as a first investigation of strong-field emission from semiconductor field emission tips illuminated by femtosecond pulses. Using a time-of-flight spectrometer, the electron energy spectrum from the silicon emitter array is shown to have features similar to the strong-field emission spectra described in 3. The energy spectrum is interpreted as a strong monoenergetic peak with a high-energy tail due to recollision of electrons with the surface, caused by the driving laser field. Interestingly, the recollision tail is shown to be significantly suppressed by a very thin native oxide layer. The authors describe a laser-induced annealing process, by which leaving high-energy light on the array for a period of tens of minutes causes the oxide to thin, leading to enhancement of the current in the main spectral peak as well as the current in the recollision tail. A model of the emission process including recollision effects and the effects of the thinning oxide layer is shown to agree with the main experimentally observed trends, although some features will need further work to explain. For now, the model's agreement with experimental trends gives confidence that the basic operation of silicon field emission tips under illumination by strong fs pulses is understood. In fact, the authors suggest that the oxide layer's prevention of recollision may even be a desirable control parameter that could mitigate the effect of spectral broadening due to electron recollision, leading to a desirable more-narrow energy spread for the source. As the first step toward understanding the operation of silicon field emitters, and in the context of high-current femtosecond-laser-triggered cathodes, this work is expected to inspire much further investigation into the suitability of field emitter arrays as high-current, short-pulse devices, as well as the potential for additional control via use of semiconductor materials for the sharp tips.