(Click here for Talk) Our group has pioneered a novel technique to measure small frequency intervals whereby a laser modulated by either an acousto/electro-optic modulator excites a neutral atom or ion beam. Each transition is multiply excited by the various laser frequency components as the laser is scanned across the resonance. The change in laser frequency is calibrated using the modulation frequency which is conveniently specified by a frequency synthesizer to an accuracy of 0.1 ppm. This frequency calibration is much simpler than using a Fabry Perot etalon. Interferometers have been plagued by numerous problems including vibrations and sensitivities to pressure and temperature fluctuations, necessitating the use of frequency stabilized lasers locked to an atomic transition to stabilize the cavity. Our work has precisely determined stark shifts, hyperfine splittings and fine structure intervals. Polarizabilities have been found with uncertainties of parts in 104.
Recently, we measured the isotope shifts of the 6,7Li D lines to determine the relative size of the 6,7Li nuclear charge radii with an accuracy of less than 1 x 10-18 meters. This is nearly is nearly an order of magnitude more precise than is possible using nuclear scattering experiments! We are currently working on measuring the fine structure separating the Li+ 1s2P 3P J=1 and J=2 states. This will not only test QED theory of two electrons systems but also precisely determine the fine structure constant.