Penning collisions of laser-cooled metastable helium atoms

We present experimental results on the two-body loss rates in a magneto-opt ical trap of metastable helium atoms. Absolute rates are measured in a syst ematic way. for several laser detunings ranging from -5 to -30 MHz and at d ifferent intensities, by monitoring the decay of the trap fluorescence. The dependence of the two-body loss rate coefficient beta on the excited state (2(3)P(2)) and metastable state (2(3)S(1)) populations is also investigate d. From these results Rie infer a rather uniform rate constant K-sp = (1 +/ - 0.4) x 10(-7) cm(3)/s.