Thanks to the relatively wide bandgap energy (3.4 eV) of gallium nitride (GaN), GaN-based technology stands out as an ideal choice for manufacturing semiconductor optical devices, including visible laser diodes. It has also paved the way for a cost-effective and efficient method to directly pump rare-earth fibres, thereby facilitating the generation of visible laser emissions. This approach now opens the path to visible femtosecond fibre lasers, which could empower diverse applications across various domains, encompassing materials processing, medical imaging and surgery, ultrafast spectroscopy, and beyond.

Researchers from the Centre d’Optique, Photonique et Laser, Université Laval, and the Département de Physique, Cégep Garneau, in Québec, Canada, have achieved a significant milestone by demonstrating the first femtosecond single-mode fibre laser operating in the visible range of the electromagnetic spectrum. This innovative study utilizes a laser design founded on praseodymium-doped fluorozirconate gain fibre pumped by a GaN-based laser diode, and employs mode locking through nonlinear polarization evolution. This laser operates in the all normal dispersion regime, producing highly chirped, similariton-like pulses with a duration of 1.6 ps and energy of 0.66 nJ. The pulses are compressed to 168 fs using a Treacy compressor. This successful demonstration envisages several promising avenues for future research, including the exploration of ultrashort pulse generation based on other visible transitions and the investigation of alternative ultrafast laser architectures.

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