2-COLOR INTENSITY SUPPRESSION OF MULTIPHOTON IONIZATION OF ATOMIC DEUTERIUM

We report a strong suppression of the three-photon ionization resonant with the 2s state of atomic deuterium at 243 nm by the introduction o f a second colour (486 nm) coupling the 2s and 4p states. This couplin g reduces the ionization probability by several orders of magnitude. T he experiment is performed using fundamental and second harmonic frequ encies of the same laser, with laser intensities up to a maximum value of 88 MW cm(-2) and an atomic target density of the order of 5 x 10(1 1) cm(-3). The production of both D+ ions and D(2s) atoms is measured as a function of the intensity of the fundamental beam (486 nm). The e xperimental data are compared with a theoretical calculation using ess ential atom + field states and taking into account the experimental la ser bandwidths.