Modeling and simulation of amplified spontaneous emission in single-mode-pumped Cr2+:ZnSe bulk amplifiers with beam propagation and equivalent input-noise seeding

Abstract

We investigate and use the beam propagation method with equivalent input noise for the simulation of narrow-band amplified spontaneous emission (ASE) and signal amplification in continuous-wave Cr²⁺:ZnSe non-waveguiding “bulk” amplifiers with non-saturating signal and ASE in different configurations with weak reabsorption. Both the incident pump at 1901 nm and the signal at 2410 nm were diffraction-limited gaussian beams. We implemented the equivalent input noise as random realizations of one photon per gridpoint, and showed that this leads to one noise photon per mode. Simulation results of between 100 and 6000 realizations were ensemble-averaged to determine the power spectral density of the ASE in a Monte Carlo approach. We validated the approach by comparing results for single-mode and multimode fiber amplifiers to those obtained with well-established fiber amplifier models. We also calculated the beam quality of the ASE, \(\:{M}_{ASE}^{2}\), from its spatial distribution. We found that under some conditions, but not all, \(\:{{M}_{ASE}^{2}}^{2}\) can serve as an estimate of an effective number of ASE modes and, together with the ASE PSD, predict the achievable signal gain. It is also possible to evaluate the PSD per unit solid angle due to spontaneous emission from the input noise seeding, and we found agreement down to the single-photon level.