COLLECTIVE EFFECTS IN 2+1 REMPI OF ATOMIC DEUTERIUM AT 243 nm B. Shortt*, F. Giammanco=86, P. J. M. van der Burgt*, and R. W. O'Neill* * Department of Experimental Physics, National University of Ireland, Maynooth, Co. Kildare, Ireland =86 Instituto Nazionale di Fisica della Materia e Dipartimento di Fisica, Universit=E0 di Pisa, 56126 Pisa, Italy We study collective effects in the transient plasma formed by the multiphoton ionization of deuterium atoms with a pulsed laser beam. Measurements of the time-dependent yields of ions and of metastable atoms are compared with fluid dynamics calculations.