Two-photon photo-ionization of the Ca $4s3d \; ^1D_2$ level in an optical dipole trap

We report an optical dipole trap for calcium. The trap is created by focusing a 488 nm argon-ion laser beam into a calcium magneto-optical trap. The argon-ion laser photo-ionizes atoms in the trap because of a near-resonance with the $4s4f \; ^1F_3$ level. By measuring the dipole trap decay rate as a function of argon-ion laser intensity, we determine the $^1F_3$ photo-ionization cross section at our wavelength to be approximately 230 Mb. Our interest in the calcium optical dipole trap is in its potential application in ultracold plasmas. Due to the high aspect ratio, a plasma generated from a dipole trap would be a 2-D ultracold neutral plasma at early times. Correlation heating is reduced compared to the 3-D case [chen04], bringing the 2-D plasma closer to the strongly-coupled regime. Furthermore, the plasma expansion depends on the exact density distribution of the initial cloud. The density profile of a dipole trap is more defined than that of a MOT, meaning that these new plasmas should have better reproducibility. \newline \newline [chen04] Y. C. Chen, et al, Phys. Rev. Lett. \bf {93}, 265003 (2004)