Düsseldorf 2007 – scientific programme
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A: Fachverband Atomphysik
A 20: Atomic Systems in External Fields II
A 20.2: Talk
Thursday, March 22, 2007, 12:00–12:15, 6G
Evidence for laser-induced relaxation in metastability exchange (ME) optical pumping (OP) of 3He — •Marion Batz1, Werner Heil1, Pierre-Jean Nacher2, and Geneviève Tastevin2 — 1Universität Mainz — 2Laboratoire Kastler Brossel, Paris
To understand current limitations of 3He MEOP, we perform systematic studies of 23S-23P0 pumping below 30mT. Experimentally, the time evolution of the nuclear polarisation M is monitored as a function of gas pressure (0.65-2.6 mbar), discharge intensity, power (0-5W) and tuning of the pump laser. An OP model is used to compute the laser-driven 23S and 23P populations and the evolution of M under combined OP, ME, and relaxation processes. Pump absorption and M growth rates measured at M=0 provide accurate relaxation-independent data to quantitatively validate the model. During M build-up, however, experimental growth rates decrease faster than expected, and systematically lower steady-state Ms are measured. To account for this, relaxation rates must be used in the model that exceed those measured in the plasma (pump off) by up to two orders in magnitude. The required additional relaxation rates are found to be proportional to the absorbed laser powers. We can directly measure the actual relaxation rates for C8 pumping (23S, F=1/2 - 23P0), the net loss of angular momentum being simply equal to the difference between the deposited one (absorbed power) and the stored one (M growth) for single-component excitation. Potential contribution of laser-enhanced relaxation processes, such as radiation trapping or collisions with metastable He2∗ molecules (more likely formed from 23P states), will be investigated.