Statistical properties of laser-cooled Ca ions in a quadrupole toroidal rf trap

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In our experiments, ions are confined in a toroidal rf trap and Coulomb coupling parameter >1 is achieved by laser cooling. In order to cool Ca+ ions, the 397 nm radiation, obtained by frequency doubling of the 794 nm radiation using a LBO crystal placed in the external cavity, and the 866 nm radiation are constructed using diode lasers.In 2001, to achieve stable radiations of 397 nm and 866 nm from diode lasers, we have constructed grating-laser-stabilization systems by means of feedback from holographic gratings in the Littrow configuration for both diode lasers. As a result, stabilization of diode lasers in frequency, intensity, and pointing has been achieved. We have controlled the Ca+ ion temperature by means of He buffer-gas-cooling ; and measured confinement time, velocity distribution function, and density profile of Ca+ ions using laser-induced fluorescence (LIF) method.In 2002, we have constructed the second 397 nm laser as a probe laser in addition to the cooling laser, in order to measure the statistical properties of laser-cooled Ca+ ions, such as velocity distribution function and density profile using LIF method. The optical feedback phase and the frequency of the grating-stabilized laser are simultaneously controlled by 1f and 3f electric feedback, respectively, using a proportional and integral (PI) feedback method, and the frequency scan of nearly 5 GHz is achieved.We have conducted LIF measurements of Ca+ ions using two toroidal rf traps ; one is 2 mm and the other is 4 mm in the distance between the neighboring electrodes (the major radius is 40 mm in both traps). Whereas the 2 mm trap has shown no LIF signals without the buffer-gas cooling, the 4 mm trap has shown the evidence for trapped Ca+ ions even at the base pressure. Laser-cooling experiments are in progress using the 4 mm trap.