High performance visible generation of Ho3+-doped all-fiber lasers

Abstract

Direct generation of visible frequency from a compact all-fiber laser while preserving high output characteristics has been a subject of research in laser technology. We investigated the high output performance of all-fiber lasers based on Ho3+-doped ZBLAN fluoride glass fiber especially operating in the deep-red band by pumping at 640 nm. Remarkably, we achieved a maximum continuous-wave output power of 271 mW at 750 nm with a slope efficiency of 45.1%, which represents, to our knowledge, the highest direct output power recorded in an all-fiber laser with a core diameter of less than 10 μm in the deep-red band. Additionally, we successfully developed a 1.2 μm all-fiber laser pumped by a 640 nm laser. We extensively investigated the correlation between these two-laser generation processes and their performances at 750 nm and 1.2 μm wavelengths. By increasing the pumping rate, we observed an efficient recycling of population through a highly excited state absorption process, which effectively returned the population to the upper laser level of the deep-red transition. Moreover, we determined the optimized conditions for such lasers, identified the processes responsible for populating the excited state energy levels, and established the corresponding spectroscopic parameters.