Abstract

Since many years, pulse energy and/or average power scaling of sub 100 fs bulk oscillator have become a very active and competing field in laser research. The major challenge in scaling up mode locked femtosecond oscillators to higher peak powers is to prevent from multi-pulse operation or intra-cavity self-focusing [1]. In order to overcome these limitations, strategies that rely on positive intra-cavity dispersion have proved that an energy scaling up to μJ level could be achieved in bulk materials [2]. Since picosecond chirped pulse intravacity are generated in a relatively large dispersion configuration (compared to soliton regime) and SESAM dynamics tends to shorten the pulse duration and do not seem the most adequate apparatus for this kind of modelocking technique. Indeed, broader spectral bandwidth is generated in soft aperture Kerr-lens mode-locking (KLM) [3]. However, KLM requires a bright pump source explaining why there is only few demonstrations of chirped pulse bulk oscillator (CPO) without SESAM particularly in ytterbium doped bulk materials. Among these materials, Yb:CALGO exhibits propitious parameters to generate ultra-short pulse in chirped pulse oscillator configuration with a high nonlinear index (10.10⁻¹⁶ cm²/W) and a flat broadband gain cross section. In this paper, we demonstrate, for the first time to the best of our knowledge, a multi-Watt CPO based on Yb:CALGO optically pumped by a diffraction-limited fiber laser delivering sub-100 fs pulse duration.

© 2015 IEEE