LASER-INDUCED RECOMBINATION OF D+

Laser induced recombination into the L shell (n = 2) of deuterium was investigated at the heavy-ion cooler storage ring CRYRING for two valu es of the electron density. The data shows the expected enhancement of radiative recombination, induced by the intense laser field applied, over the spontaneous case. Like in previous measurements, a strong int ensity below the photoionization threshold was observed. Qualitatively , this gain is described by an average field induced threshold shift m odel. However, when reducing the electron density by roughly a factor of two, the effective field increased by an order of magnitude. This s urprising result indicates that the precise origin of the observed fie lds is not simply related to the known field sources.