LINE-SHAPE OF A DOPPLER-FREE 2-PHOTON TRANSITION IN A METASTABLE NEONBEAM

We present a model of the line shape of a Doppler-free two-photon tran sition in a metastable neon beam. This model considers the ac Stark ef fect, the Gaussian profile of the laser beam, and the depletion, or bl eaching, of the metastable state as the atoms cross the laser. The mod el fit the experimental data well and was recently used to verify the time-dilation effect at an accuracy of a few ppm.