title: Effective temperature of an ultracold electron source based on near-threshold photoionization.
abstract: We present a detailed description of measurements of the effective temperature of a pulsed electron source, based on near-threshold photoionization of laser-cooled atoms. The temperature is determined by electron beam waist scans, source size measurements with ion beams, and analysis with an accurate beam line model. Experimental data is presented for the source temperature as a function of the wavelength of the photoionization laser, for both nanosecond and femtosecond ionization pulses. For the nanosecond laser, temperatures as low as 14 ± 3 K were found; for femtosecond photoionization, 30 ± 5 K is possible. With a typical source size of 25 μm, this results in electron bunches with a relative transverse coherence length in the 10⁻⁴ range and an emittance of a few nm rad.
authors.affiliation: Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
authors.forename: W J
authors.initials: WJ
authors.lastname: Engelen
authors.forename: E P
authors.initials: EP
authors.lastname: Smakman
authors.forename: D J
authors.initials: DJ
authors.lastname: Bakker
authors.forename: O J
authors.initials: OJ
authors.lastname: Luiten
authors.forename: E J D
authors.initials: EJ
authors.lastname: Vredenbregt
keywords: Coherence; Photoionization; Ultracold electron source; Ultrafast electron diffraction