Two-photon photo-ionization of the Ca 4s3d 1D2 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 1F3 level. By measuring the dipole trap decay rate as a function of argon-ion laser intensity, we determine the 1F3 photo-ionization cross section at our wavelength to be approximately 230 Mb. 
J. E. Daily, R. Gommers, E. A. Cummings, D. S. Durfee, and S. D.   Bergeson