The two-and three-photon resonant ionization of Ca has been studied. Calcium atoms in the thermal atomic beam were ionized from the ground 4s 2 1 S 0 state by three-photon absorption. The ion signals exhibited resonances attributed to the two-photon transition 4s 2 1 S 0 -4s6s 1 S 0 and three-photon transitions due to 3d17f, . . . , 3d22f 1 P 1 , 3d19p, . . . , 3d24p 1 P 1 , 3d18f, . . . , 3d19f 3 P 1 and 3d23f, 3d25f 3 D 1 autoionizing states. A simple theoretical model was used to reproduce the main features of the observed spectra due to the two-photon resonant ionization.

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Experimental values of the electron-impact coherence parameters (EICP) are reported for electron-impact excitation of the 4 1 P 1 state of Ca. The results have been obtained using electron-photon coincidence techniques for incident electron energies of 45 and 60 eV and scattering angles of 15 • , 20 • , 25 • , 30 • , 35 • and 40 • . EICP values determined at 45 eV are compared with similar data obtained by other groups with coincidence and optical pumping methods. Our data do not show a disagreement with the theoretical calculations based on a relativistic distorted-wave approximation (RDWA) that was reported for earlier experimental coincidence results.

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Measurements are reported for the polarization of the fluorescence arising from the excitation of the state of Ca atoms detected in coincidence with electrons scattered with a suitable energy loss. The excitation parameters have been determined at an electron incidence energy of 100 eV for five scattering angles between and . Calculations for the measured parameters are also performed using the relativistic distorted-wave approximation. The theoretical results are presented and compared with the experimental data.