Designing a Broadband Pump for High-Quality Micro-Lasers via Modified Net Radiation Method

TL;DR

This paper introduces a theoretical framework based on the modified net radiation method to optimize broadband pump design for high-quality micro-lasers, enabling efficient non-resonant and solar-pumped laser operation.

Contribution

It develops a robust, fast, and low-complexity model for energy transfer in cascade sensitizer and laser media, guiding optimal pump parameters for micro-lasers.

Findings

Optimal pump absorption is below the maximum, unlike conventional lasers.

Numerical results align well with experimental data on Nd:YAG lasers.

The model facilitates the design of broadband-pumped high-quality micro-lasers.

Abstract

High-quality micro-lasers are key ingredients in non-linear optics, communication, sensing and low-threshold solar-pumped lasers. However, such micro-lasers exhibit negligible absorption of free-space broadband pump light. Recently, this limitation was lifted by cascade energy transfer, in which the absorption and quality factor are modulated with wavelength, enabling non-resonant pumping of high-quality micro-lasers and solar-pumped laser to operate at record low solar concentration. Here, we present a generic theoretical framework for modeling the absorption, emission and energy transfer of incoherent radiation between cascade sensitizer and laser gain media. Our model is based on linear equations of the modified net radiation method and is therefore robust, fast converging and has low complexity. We apply this formalism to compute the optimal parameters of low-threshold solar-pumped lasers. It is revealed that the interplay between the absorption and self-absorption of such lasers defines the optimal pump absorption below the maximal value, which is in contrast to conventional lasers for which full pump absorption is desired. Numerical results are compared to experimental data on a sensitized Nd:YAG cavity, and quantitative agreement with theoretical models is found. Our work modularizes the gain and sensitizing components and paves the way for the optimal design of broadband-pumped high-quality micro-lasers and efficient solar-pumped lasers.