The 1s-2s energy interval in the muonium (mu(+)e(-)) atom has been measured
by Doppler-free two-photon laser spectroscopy. A value of 2455528941.0(9.8
) MHz has been obtained in good agreement with quantum electrodynamics (QED
). The muon-electron mass ratio can be extracted and is found to be 206.768
38(17). The measurement may also be interpreted as a determination of the m
uon-electron charge ratio as -1- 1.1(2.1) . 10(-9). Corresponding measureme
nts in deuterium using the same experimental setup confirmed the validity o
f the applied analysis procedure.