A coupling model for amplified spontaneous emission in laser resonators

Abstract

The competition between amplified spontaneous emission (ASE) and main laser in solid-state laser resonators is investigated both theoretically and experimentally. A coupled model using the spatial volume integral instead of the Monte Carlo type raytrace technique is proposed to depict ASE in the laser resonators. This model is able to evaluate all possible reflections at both the polishing surface and the diffusive side, to calculate ASE for an inhomogeneous gain distribution, and to include the spectral correction. An experiment is carefully designed to verify the theoretical model and to investigate the distinct physical properties caused by the coupling between ASE and the laser oscillations. The experimental data exhibit an excellent agreement with the theoretical predictions. According to that model, we confirm that ASE in thin-disk lasers can be characterized approximately by the product of the threshold gain of the resonator and the diameter of the disks, as laser modes are highly overlapped with the pumping beam. Theoretical evaluation shows that the scattering characteristic of the disk side impacts on ASE significantly. Furthermore, we point out that ASE decreases output laser power by affecting threshold pumping power, while slope efficiency is not changed by ASE. This observation provides us with a simple way to estimate the decrease of the optical efficiency by ASE.

Amplified spontaneous emission intensity at the side surface of thin disk lasers

“…6 The flow chart of simultaneous calculations of ASE intensity and output power of a disk laser using Eqs. ( 7)- (13). The results of these calculations are demonstrated in Fig.…”

“…ASE signal intensity for disk lasers can be obtained by calculating this coefficient for disk geometry. It has been shown that ASE intensity is proportional to the multiplication of the threshold gain coefficient by the diameter of the disk 13 . Slezak et al 14 .…”

“…It has been shown that ASE intensity is proportional to the multiplication of the threshold gain coefficient by the diameter of the disk. 13 Slezak et al 14 presented a disk laser with a multilayer structure with different absorption coefficients. In this structure, the outer layer has a different medium from the active laser medium resulting in higher ASE absorption.…”

High-power, high-brightness solid-state laser architectures and their characteristics

“…For highenergy laser systems, where high inversion is crucial, additional transparent, so called 'anti-ASE caps' are used to avoid trapping of the spontaneous emission within the amplifying disk. There are a number of publications on ASE in disk lasers, mostly relying on ray-tracing for the ASE and the rate equation for the laser process, for various geometries, sometimes also taking into account the temperature [50,[91][92][93][94][95][96][97][98][99].…”

Numerical Simulations of Amplified Spontaneous Emission in Yb:YAG Thin-Disk Amplifiers

“…Peterson et al [17] accounts for the heating of the thin disk and a spectral power distribution by a Lorentzian spectral power distribution of amplified spontaneous emission. Scattering of amplified spontaneous emission at the cylinder jacket was investigated by Su et al [24] with a bidirectional scattering model. [25,26] focused on the non-uniform temperature distribution and Chen et al [15] shows an analysis of the spectral power distribution of amplified spontaneous emission.…”