In this work we investigate on the characteristics of electron beams generated by three photocathodes (PC), one based on Cu sample and two on different nanodiamond (ND) layers. Specifically, the active layers of the ND-based PCs consisted of untreated and hydrogenated ND particles, 250 nm in size, sprayed on p-doped silicon substrates. We show photoemission measurements, carried out by a KrF nanosecond excimer laser (λ= 248 nm; photon energy 5 eV) in a vacuum chamber at 10− 6 mbar. We also make a study of the n-photon emission processes for all the PCs. The obtained results showed QE values of the ND-based photocathodes higher than that of the reference Cu one. In particular, the hydrogenated ND-based PC showed the highest QE thanks to the negative electron affinity of its surface.