Wave optics modelling of amplified spontaneous emission

A laser works by amplified spontaneous emission (ASE) of inverted atomic ions confined in an amplifier of rod-like geometry, such that ASE radiation is directed out of both ends of the rod. The forward and backward ASE waves are coupled through the population-rate equations and cause the saturation of the lasing transition (gain saturation). Diffraction of the waves in the transverse direction is responsible for the radiation pattern (angular distribution) observed on a distant screen and for the degree of spatial coherence of the radiation. Refraction of the light also occurs due to spatial gradients in the electron density. In order to describe this situation a code has been developed which numerically solves paraxial Maxwell's equations in the time and two spatial dimensions. The code uses the Peaceman-Rachford Alternating-Direction-Implicit algorithm and is benchmarked against laboratory DYE-LASER experiments. 4 refs., 1 fig.