title: Pulse length of ultracold electron bunches extracted from a laser cooled gas.
abstract: We present measurements of the pulse length of ultracold electron bunches generated by near-threshold two-photon photoionization of a laser-cooled gas. The pulse length has been measured using a resonant 3 GHz deflecting cavity in TM110mode. We have measured the pulse length in three ionization regimes. The first is direct two-photon photoionization using only a 480 nm femtosecond laser pulse, which results in short (∼15 ps) but hot (∼104K) electron bunches. The second regime is just-above-threshold femtosecond photoionization employing the combination of a continuous-wave 780 nm excitation laser and a tunable 480 nm femtosecond ionization laser which results inbothultracold (∼10 K)andultrafast (∼25 ps) electron bunches. These pulses typically contain ∼103electrons and have a root-mean-square normalized transverse beam emittance of 1.5 ± 0.1 nm rad. The measured pulse lengths are limited by the energy spread associated with the longitudinal size of the ionization volume, as expected. The third regime is just-below-threshold ionization which produces Rydberg states which slowly ionize on microsecond time scales.
authors.forename: J G H
authors.initials: JG
authors.lastname: Franssen
authors.affiliation: Department of Applied Physics, Eindhoven University of Technology , P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
authors.forename: T L I
authors.initials: TL
authors.lastname: Frankort
authors.forename: E J D
authors.initials: EJ
authors.lastname: Vredenbregt
authors.forename: O J
authors.initials: OJ
authors.lastname: Luiten