a Scanning electron micrograph of a representative single-tip emitter (Star 1). The tips appear broader than in transmission electron micrographs and nanostar statistics due to a 3 nm Pt film deposited prior to electron imaging to improve sample conductivity and image quality. This added thickness is therefore subtracted from the measured nanostar dimensions for modeling and simulation. Scale bar: 50 nm. b Modeled nanostar geometry with calculated linear and eighth-order (four-photon) surface-normal electric field enhancements. All measurements and calculations are performed on-resonance at 900 nm and 0° polarization. The ITO-coated substrate and HEPES ligands (not shown) are included in the field calculations. c Experimental and d theoretical velocity map images of the vz-projected photoelectron distribution. e Reconstructed experimental and f theoretical 3D velocity distributions, showing iso-probability surfaces at 75%, 50%, and 25% maximum along with the overall vz projections. g Angular distributions and h electron kinetic energy distributions determined from xy slices of the 3D experimental and theoretical distributions.