Intense electron emission due to picosecond laser-produced plasmas in high gradient electric fields

Abstract

Picosecond laser pulses at a wavelength of 266 nm have been focused onto a solid metal cathode in coincidence with high gradient electric fields to produce high brightness electron beams. At power densities exceeding 109 W/cm2, a solid density plasma is formed and intense bursts of electrons are emitted from the target accompanied by macroscopic surface damage. An inferred ∼1 μC of integrated charge with an average current of ∼20 A is emitted from a radio-frequency cavity driven at electric field gradients of ∼80 MV/m. In another experiment, where a dc extraction field of ∼6 MV/m is used, we observed an electron charge of ∼0.17 μC. Both results are compared with the Schottky effect and the Fowler–Nordheim field emission. We found that this laser-induced intense electron emission shares many features with the explosive electron emission processes. No selective wavelength dependence is observed in the production of the intense electron emission in the dc extraction field. The integrated electrons give an apparent quantum efficiency of ∼1.2%, which is one of the highest reported to date from metal photocathodes at these photon energies.

Photoemission from diamond and fullerene films for advanced accelerator applications

“…Using published values for DT's (>2. 10' W cm-' for single crystal diamond with 193 rim, 15 ns pulses [47], and lo9 W cm-' for copper and 266 nm-112 ps pulses [48]) and the QE's obtained in this experiment with 217 nm light for the boron-doped diamond film and with 266 nm light for the mirror polished copper, one can conclude that the product (QE.DT) for diamond films (2.6 . lop4.…”

High-Charge S-Band Photocathode RF-Gun and Linac System for Radiation Research.

“…14) Figure 3 shows the measured results of the bunch charge and length vs. the relative laser injection phase. A con-cal QE value of the Cu cathode for the same type guns under similar conditions is ∼5×10 −5 , 8,17) but the highest QE of 5×10 −4 for the Cu cathode with 120 MV/m acceleration field was reported. 18) After the gun had been equipped with the additional getter pump, a similarly QE was achieved.…”

600 eV falcon-linac thomson x-ray source

“…The peak charge per pulse that has been measured to date is 0.4 nC, and was purposely limited due to the small UV spot size on the photocathode. A full nC of charge extraction at high gradient with a small spot size would approach the region where cathode damage can result [9].…”