This proposal is to continue support for a research program on cold, dense, Rydberg Gases at Colby College. The Rydberg atoms in this environment are strongly coupled by the dipole interaction, and these forces can have a dramatic influence on the atomic motions. In particular, cold Rydberg atoms have been observed to spontaneously evolve to plasma, a process that is initiated by dipole forces. Rydberg states are also formed by three-body electron-ion recombination in ultra cold plasmas that are created by photoionization of cold atoms. There is theoretical and experimental evidence that the presence of Rydberg atoms may play a role in control of the electron temperature in such plasmas. Dipole forces between Rydberg atoms can lead to the formation of novel molecular systems, which may be identified by spectroscopic means. A rubidium magneto-optical trap (MOT) has been constructed (density 1 x 1010 cm-3, temperature 100 uK). Cold Rydberg atoms are selectively excited using a pulsed laser. In order to perform high- resolution spectroscopy of atomic or molecular states, a tunable millimeter wave source has been built. The high resolution available from this source also enables one to "tag" a particular Rydberg state, and monitor the population dynamics of this state with great precision. In the immediate future, three broadly related areas will be pursued. Measurement of Rydberg lifetimes in hiught n states, temperature control in ultra cold plasmas and the spectroscopy of Rydberg molecules .
