LASER-PULSES AS MEASUREMENTS - APPLICATION TO THE QUANTUM ZENO EFFECT

Short pulses of a probe laser have been used in the past to measure wh ether a two-level atom is in its ground or excited state. The probe pu lse couples the ground state to a third, auxiliary, level of the atom. The occurrence or absence of resonance fluorescence were taken to mea n that the atom was found in its ground or excited state, respectively . In this paper we investigate to what extent this procedure results i n an effective measurement to which the projection postulate can be ap plied, at least approximately. We discuss in detail the complications arising from an additional time development of the two-level system pr oper during a probe pulse. We extend our previous results for weak pro be pulses to the general case and show that one can model an ideal (pr ojection-postulate) measurement much better with a strong than a weak probe pulse. In an application to the quantum Zeno effect we calculate the slow-down of the atomic time development under n repeated probe p ulse measurements and determine the corrections compared to the case o f n ideal measurements.