Nonresonant multiphoton ionization of calcium atoms in an intense laser field

We have studied the single and double nonresonant multiphoton ionization of calcium atoms using both 532-nm and 1.06-{μ}m radiation. These studies were conducted in the intensity regime of 10¹⁰--10¹³ W/cm². We use mass and angularly resolved electron-energy analysis in an attempt to gain insight into the dominant mechanisms responsible for ionization. An analysis is presented for intensity- and frequency-dependent results, and electron angular distributions are reduced in terms of atomic parameters derivable from lowest-order perturbation theory.