Compact fiber-based compression of a 1 W, 76 MHz Yb laser to 15 fs for broadband ultrafast applications
We demonstrate a compact scheme for generating sub-20-fs pulses from a commercial ytterbium femtosecond laser delivering 80 fs pulses at 76 MHz repetition rate with 1 W average power. Spectral broadening is achieved in a photonic crystal fiber (PCF), followed by dispersion compensation using broadband chirped mirrors. By systematically varying the fiber length and coupled power, we investigate the interplay between nonlinear spectral broadening and higher-order dispersion. While the spectral bandwidth increases monotonically with fiber length, the achievable pulse duration exhibits a clear minimum due to accumulation of uncompensated higher-order phase, primarily third-order dispersion. An optimal fiber length of 80 mm yields nearly transform-limited 15.4 fs pulses. Shorter fibers provide insufficient broadening, whereas longer fibers, despite offering larger bandwidth, compromise the pulse temporal quality. Stable sub-20-fs operation is demonstrated at average powers exceeding 600 mW, and noise measurements indicate that the system performance is limited by the Yb seed laser. These results identify an optimal nonlinear interaction regime in PCF-based compression and establish a practical design rule linking spectral broadening to higher-order phase for compact ultrafast Yb laser sources.