Light Management for Enhancing Optical Gain in a Solar‐Pumped Fiber Laser Employing a Solid‐State Luminescent Solar Concentrator

Abstract

Optical gain of 8.3 km−1 is obtained in a neodymium‐doped silica fiber under simulated sunlight (intensity = 2.1 kW m−2). The fiber gain medium (length = 50 m) is coiled and attached to a solid‐state luminescent solar concentrator (LSC) disk (diameter = 180 mm). The disk/fiber unit is placed in a cavity comprising highly reflective (HRM) and dichroic (DM) mirrors to increase the photon confinement by a factor of 2.2 compared with a liquid LSC (also employing HRM/DM). The enhancement is mainly due to the air gap between HRM/DM and LSC, which affords total internal reflection (TIR) in the solid‐state LSC and an ideal boundary condition for the multilayer mirrors. The numerical calculations indicate that an additional 2.2‐times enhancement is achievable with a side wall exhibiting 90% diffuse reflection. This has been experimentally confirmed (1.9‐times optical‐gain enhancement is realized by adding a polytetrafluoroethylene side‐wall reflector). Overall, the solid‐state LSC‐based solar‐pumped laser (SPL) comprising reflective side walls exhibits a gain factor of 4.2, which is superior to its liquid‐state predecessor. Further improvements employing a solid‐state LSC design and fiber optimization will facilitate the market penetration of SPLs.

Keywords

• light management
• luminescent solar concentrator
• optical fibers
• ray tracing
• solar-pumped laser