We demonstrate a combination of an isotopically purified atom beam and a magneto-optical trap which enables the single atom detection of all stable isotopes of calcium (40, 42, 43, 44, 46 and 48). These isotopes range in abundance from 96.9 % ( 40 Ca) to 0.004 % ( 46 Ca). The trap is loaded from an atomic beam which is decelerated in a Zeeman slower and subsequently deflected over an angle of 30 • by optical molasses. The isotope selectivity of the Zeeman slower and the deflection stage is investigated experimentally and compared with Monte Carlo simulations.

We demonstrate a spectroscopy method that can be applied in an atomic beam, light-pressure-induced spectroscopy ͑LiPS͒. A simple pump and probe experiment yields a dispersivelike spectroscopy signal that can be utilized for laser frequency stabilization. The underlying principles are discussed and compared to Monte Carlo simulations. The shape of the dispersive signal is well described by the simulations. The zero crossing point of the signal is redshifted with respect to the atomic resonance by ϳ3 MHz ͑one-tenth of the natural linewidth͒ and depends slightly on the laser intensity. The shift of the zero crossing is determined by laserinduced fluorescence and compared with results of Doppler-free saturation spectroscopy. To check the potential of LiPS for frequency stabilization purposes, it was used to frequency-stabilize the laser for 400 min. Frequency fluctuations of only 0.12 MHz were measured.

In our experiment we aim at the detection of the rarest, naturally occuring calcium isotope 41 Ca by means of atom trap trace analysis. On basis of single-atom detection of 46 Ca our present sensitivity for 41 Ca is estimated to be 1 atom per hour at an abundance of 10 À12 : To reach a sensitivity at the level of natural abundance, which is 10 À14 , we need to reduce atomic beam losses. To achieve this, optical compression of the atomic beam is a promising option. We use Monte Carlo Simulations to demonstrate that optical compression of the atomic beam increases throughput of the atomic beam as well as isotope selectivity.

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