Laser photoexcitation of Rydberg states in helium with n > 400

摘要: Helium atoms travelling in pulsed supersonic beams have been photoexcited from the metastable 1s2s 3S1 level to Rydberg states with principal quantum numbers exceeding 400 by resonance-enhanced two-colour two-photon excitation using narrow-bandwidth CW laser radiation. To achieve this, photoexcitation region was shielded and stray electric fields cancelled a cubic arrangement of 80 mm × copper plates. The excited were detected field ionisation downstream this region. Comparison experimental spectra results calculations indicate that at position state reduced as low 160 μV cm–1. Using helium these experiments minimises temporal changes resulting surface adsorption. Measurements performed 70 h apart rate change on order 2 cm–1 per h, making ideally suited probes for high precision electrometry spectroscopy involving less readily available species such positronium or antihydrogen.