Abstract

‘Burst’ operating mode of mode-locked fiber lasers, presented for the first time in [1], has recently gained high potential in hard and soft tissue ablation [2,3]. Pulse bursts consist of temporally closely spaced pulses, which during the ablation prevent rapid cycles of material heating and cooling. Bursts are typically generated at low repetition rate, which allows lower average power at the same level of the energy, therefore, avoiding long-term heat accumulation in the material. Hence, burst mode operation is superior in terms of energy required, ablation speed and avoidance of thermal effects, compared to uniform pulse trains. Currently to achieve the pulse burst generation, several acousto-optic modulators are introduced in the laser system to crop window of seed laser output pulse train or direct pulse burst generation from highly-pumped lasers [4,5]. Here we propose a new concept of generating such pulse bursts using an ultralong mode-locked fibre laser, based on quasi-lossless concept, where the short laser cavity is enhanced with a long fiber span, forming a distributed Raman amplifier. This relaxes the restriction on non-compensated losses inherent in traditional ultralong soliton lasers and enables effective wave breaking and multiple-pulsing phenomena.

© 2017 IEEE