Power and Energy Scaling of Short-Pulsed Fiber Lasers : From Fundamental to Structured Beam Profiles

Laser technology has become integrated into our daily lives across science, industry, and medicine. Short-pulsed laser systems, in particular, received recognition as in-dispensable tools, driving the demand for sources of higher power and energy with various spatial profiles. Moreover, short-pulsed structured light with complex optical fields has opened up unprecedented opportunities in various applications due to its unique properties. However, power and energy scaling in such lasers are mainly limited by nonlinear and thermal effects in fiber amplifiers and by thermal loading, optical damage, and mode degradation in structured-light generation methods. This thesis demonstrates solutions to these limitations through two research directions: (1) power and energy scaling of short-pulsed Gaussian beams using monolithic all-fiber spun tapered double-clad fibers (sT-DCFs), and (2) power scaling of structured light via a filled-aperture coherent beam combining (CBC) technique. In the first part of this work, I demonstrate several significant achievements of the short-pulsed system: 50-ps pulses with 2 MW peak power at 1 MHz and 625 W average power at 20 MHz, 20-ps pulses at 645 W at 1 GHz, and 1.6 mJ/8ns narrow-linewidth nanosecond pulses with a high degree of spatial coherence. These achievements confirm the outstanding potential of all-fiber sT-DCFs for efficient amplification of short pulses at high power and energy levels. The second part of the thesis explores power scaling of structured light, with optical vortices (OVs) as a representative case, using the CBC technique. Short-pulsed OVs with average powers exceeding 100 W with topological charges of ℓ = 1, 5 and 8 were demonstrated with combining efficiencies above 90%. Off-axis digital holography confirms the high modal purity of the OVs by analyzing their phase and intensity profiles. Overall, this work advances the state of the art in short-pulsed laser technology by demonstrating both the performance scaling of sT-DCF-based amplifier systems and the power scaling of structured light through the CBC technique.