Doppler-free two-photon spectroscopy of one electron atoms using pulsed lasers
In two independent experiments, frequency doubled pulse amplified dye laser light has been used in performing Doppler-free two-photon spectroscopy of the 1S½−2S½ transition in atomic hydrogen and muonium. Absolute values gained for the 1S½−2S½ transition frequencies were 2466 061 416(9) MHz and 2455 528 964(72) MHz for hydrogen and muonium respectively. Values for the ground state Lamb shifts were inferred to be 8171(9) MHz for hydrogen and 8079(73) MHz for muonium. All results were found to be in agreement with current quantum electrodynamic (QED) theory. Assuming QED theory to be accurate, then the hydrogen experiment yielded a new value for the Rydberg constant of 109 737 31.58(4) m−1, which is in agreement with other independent measurements. A separate experiment demonstrated a novel and general technique for efficiently frequency doubling mode-locked laser light, based on second harmonic generation inside an actively stabilised external ring enhancement cavity. When applied to a synchronously pumped mode-locked dye laser, over 100mW average power of tunable light around 243nm was available from the system corresponding to crystal conversion efficiencies in excess of 55%. A simple theoretical model successfully described the performance of this system. FM sideband frequency stabilisation of mode-locked lasers is treated both theoretically and experimentally. For the mode-locked dye laser, a frequency stability to within 500kHz relative to a reference interferometer was routinely possible. The frequency stabilised tunable uv light is ideal for performing Doppler-free coherent multiple pulse spectroscopy and may find application in the synchronous pumping of optical parametric oscillators or in selectively breaking chemical bonds.