The excitation of a linear quantum oscillator (LQO) upon a collision with a charged particle moving in a rectilinear trajectory is analyzed. The probability and the cross section of the process are calculated beyond the framework of perturbation theory for different charges of the incident particle, including multiply charged ions. The excitation between the LQO stationary states, as well as total excitation from the ground state, are considered. The characteristic features of the process depending on the problem parameters are analyzed.

The paper is devoted to the theoretical investigation of time dependences of quantum oscillator excitation by electromagnetic pulses for arbitrary values of field amplitude in the pulse. We consider the harmonic oscillator without relaxation and excitation between stationary states. The general formula for excitation of quantum states as function of time is derived in terms of instant energy of associated classical oscillator in the field of electromagnetic pulse. Thus, it is established that time dependence of quantum oscillator excitation is completely determined by the energy of the associated classical oscillator at given moment of time. Using derived expression time dependence of quantum oscillator excitation is investigated in details including total excitation from ground state, excitation from excited states, total excitation probability and corresponding excitation spectra.

The features of excitation of a quantum harmonic oscillator under the action of short laser pulses were studied numerically and analytically for transitions between stationary states. The probabilities of oscillator excitation (during the action of a pulse) as a function of the pulse duration and carrier frequency were calculated for arbitrary values of the electric field amplitude. It is shown that with increase in field amplitude the number of maxima in the spectrum and the excitation probability on the pulse duration increases. For laser pulses with different types of envelopes, analytical expressions were obtained that describe the positions of additional maxima in the excitation probability and the criteria for their appearances. Presented below are the results of numerical calculations for the probability of transition from an excited state to overlying state as a function of carrier frequency and laser pulse duration.