Theory of Relaxation Spikes in Two-Level Laser Amplifiers

Theodor W. Hänsch, P. E. Toschek

S. V. Manakov

J.H. Shirley

A simple maser model consisting of a single-mode field coupled to N identical two-level atoms is presented. The assumption of negligible statistical correlation between the atoms and the field, permits the Heisenberg equations of motion to be replaced by a self-consistent set of ordinary nonlinear differential equations. Relaxation terms and an energy source are introduced phenomenologically. The resulting equations exhibit a threshold, stable and unstable steady states, relaxation oscillations and, sometimes, spiking. The dynamic equations for the hydrogen maser and the rate equations of laser theory are derived as special cases. Also discussed are the maser amplifier, locking of a maser to an external signal, and the effects of cavity thermal noise.

A. E. Glassgold, Dennis Holliday

Alexander A. Zabolotskii

The inverse scattering transform method is used in a study of the evolution of light pulses in an initially inverted three-level medium of the Λ type. An asymptotic solution describing the profile of the first spike is obtained for small-area priming pulses. It is shown that this asymptote is determined entirely by the initial populations of the lower levels and by the profile of the priming pulses. A special case of this problem is the propagation of two-component light in a laser amplifier using the degenerate J = 0–J = 1 transition.

Earl L. Steele

This paper describes a model and provides the mathematical formulation for describing the spike pulsing phenomenon observed in optically pumped three-level lasers. The model is based on the pumping of electrons from a ground state to an excited pump band from which they relax very rapidly to the excited laser level. With population inversion then achieved, laser action starts and repetitive pulses with decreasing amplitude are generated; the pulses then damp out and the laser output reaches a steady state as long as sufficient pump radiation energy is available. The equations describing the system in terms of the population inversion and photon density are nonlinear. However, approximations are made which permit the required relations between the transition rates to be established for such action to progress. The time variation of the population inversion and the photon density at the laser frequency are obtained for both the pumping time interval and the stimulated emission laser region.