Narrow-band pulsed electron source based on near-threshold photoionization of Cs in a magneto-optical trap

• Published in: Physical review. A 2020-01, Vol.101 (1), Article 013424
• Main Authors: Fedchenko, O., Chernov, S., Schönhense, G., Hahn, R., Comparat, D.
• Format: Article
• Language: English
• Subjects: Atomic Physics; Instrumentation and Detectors; Physics; Quantum Physics
• ISSN: 2469-9926; 2469-9934
• DOI: 10.1103/PhysRevA.101.013424

The newly developed method of time-of-flight (TOF) momentum microscopy was used to analyze the cold electron emission from a Cs three-dimensional magneto-optical trap (MOT). Three-step resonant photoionization was implemented via two intermediate states (6P 3/2 pumped with an 852-nm laser and 7S 1/2 with a 1470-nm laser) and a tunable femtosecond (fs) Ti:sapphire laser for the final ionization step. The magnetic field of the MOT is switched off during the photoionization step. The natural bandwidth of the fs laser is reduced to 4 meV using optical spectral filters. Precise tuning of the photon energy makes it possible to observe the transition regime between direct photoemission into the open continuum and field-induced ionization of highly excited Rydberg states. The paths can be identified by their characteristic dependency on the extraction field and on the Ti:sapphire polarization. TOF analysis allowed us to disentangle the ionization paths and the dependence of the spatiotemporal distribution of the cold electrons on the polarization of the ionizing laser.