Nat. Phys. http://doi.org/bw2k (2016)

Field-controlled light–matter interactions, such as those between laser pulses and metallic nanotips, are important for attosecond science. William Putnam and co-workers have now investigated strong-field photoemission from metallic nanoparticles supporting localized surface plasmon resonances. The device operates under ambient conditions and is similar to a microscale phototube, the photocathode — a layer of indium tin oxide (ITO) topped by an array of gold nanoparticles — is separated from the ITO anode by a micrometre-wide gap. The team illuminates the nanoparticle emitters with femtosecond pulses of tunable pulse energy at a central wavelength of 1,177 nm (with the plasmon resonances ranging from 895 nm to 1,256 nm). Tight focusing of the laser pulses at an incident peak field of 1.2 V nm−1 drives photoemission currents up to ∼30 nA from the nanoparticles. In the strong-field regime, the emission process is expected to resemble tunnelling and experimental estimates indicate a field enhancement of ∼32.