The key benefits of an ultrafast laser are broadband spectrum, high energy density, and high time resolution. High-energy and high peak-power ultrafast lasers have found extensive applications in frontier science and industry domains like photomedicine, ultrafast physics, and advanced manufacturing.
High power/energy ultrafast fiber laser technologies are of interest to researchers at the National University of Defense Technology (NUDT), China, under the direction of A./Prof. Can Li and Prof. Pu Zhou. The advantages of fiber lasers include high conversion efficiency, great beam quality, and a compact and versatile system.
However, undesired nonlinear effects severely limit the pulse energy and peak power scaling of ultrafast fiber lasers, which are constrained by the long transmission length and small mode field area. Generally speaking, the mode field diameter (MFD) determines the threshold of nonlinear effects.
To counteract the nonlinear effects, the fiber MFD cannot be increased arbitrarily since this would cause high-order mode (HOM) contents to appear and degrade the output beam quality. The tapered fiber might be able to balance the nonlinear effects and beam quality due to its longitudinally increased core/cladding diameter.
A high-energy and high peak power monolithic CPA system with near diffraction-limited beam quality (M2=1.20) was shown by the researchers by combining a tapered confined-doped fiber with a high-order dispersion correction approach.
After pulse compression, the maximum pulse energy of 126.3 μJ was attained with a pulse duration of 401 fs and a peak power of 207 MW. This is the highest peak power produced by a monolithic fiber laser that has ever been documented.
Wang, T., et al. (2023) Monolithic tapered Yb-doped fiber chirped pulse amplifier delivering 126 μJ and 207 MW femtosecond laser with near diffraction-limited beam quality. Frontiers of Optoelectronics. doi:10.1007/s12200-023-00087-y