Laser Excitation of the Muonium1S−2STransition

Abstract

We present evidence for the excitation of the two-photon Doppler-free $1S-2S$ transition in muonium. Thermal muonium atoms were produced in vacuum by a 27.5-MeV/c pulsed positive-muon beam incident on a powdered Si${\mathrm{O}}_2$ target. Transitions were induced by the light from a frequency-doubled pulsed dye laser and were detected by photoionization of the $2S$ state. The $1S(F=1\mathrm{})\mathrm{}\to 2S(F=1\mathrm{})\mathrm{}$ transition frequency is within 300 MHz of the QED prediction.