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.

This article describes measurement of oscillator instabilities by a method using the real-time multichannel scaler (RTMS). A theoretical model for such application is also considered. The general problem of the oscillator instability measurements in time domain is discussed. The results of oscillator instability measurements using the real-time multichannel scaler and a time interval analyzer are compared. The full range of application of this method is up to 7E-7 and depends strongly on the RTMS construction. We present the results of oscillator instability measurements of the order of 3E-5, using the RTMS with a resolution of 3.13 ns and the range of operation 3.28 ms.

The construction of a fast, real-time multichannel scaler and its application to the analysis of signals composed of series of pulses are described. The device allows measurements in time intervals of up to 1.3 ms with a single time-channel width of 5 ns and accepts input pulses of 2 ns in width. The capacity of the single time channel and the repetition rate are up to 32 bits and 50 per second, respectively. Applications to laser deposition/ionization and three-photon-ionization experiments involving pulsed laser sources are briefly discussed.

The investigation of thresholds for the occurrence of the collective effects (plasma effects) in the two-photon resonant, 4s2 1 S0 to 4s6s 1 S0 , three-photon ionization of calcium atom is presented. Our experiments were carried out using an excimer/dye laser system scanned through the resonance two-photon transition. Ions and electrons were produced in an interaction region inside the vacuum chamber where the laser beam and atomic Ca beam intersect. The plasma effects (collective effects), i.e. the effects caused by the action of ions/electrons created in the interaction region on charges leaving that zone are highlighted and analysed. The yields and time-of-flight (TOF) distributions for ions produced in such three-photon ionization of atomic calcium have been investigated as a function of laser intensity and laser detuning. We present the results of simple theoretical models for the plasma effects such as 40 Ca+ and 44 Ca+ time separation in TOF distribution as well as a model based on atomic physics for the time shift and asymmetry of 40 Ca+ due to an increase of the laser intensity. These results are compared with experimental data which are obtained first time for such a heavy element in the periodic table.