Abstract

High-energy and high-average-power ultra-short pulse laser sources have been an interesting research area and among them, fiber-based short-pulse lasers gain increasing interest over the recent decade. Mode-locked fiber lasers have attracted considerable attention due to their inherent properties such as compactness, lack of misalignment, high efficiency and immunity against thermo-optical issues. The development of low-nonlinearity large-mode-area fibers (LMA) opens up new possibilities for energy scaling as has been demonstrated recently by the achievement of more than 16 nJ from a femtosecond Yb-doped fiber laser operating in the solitonic regime [1]. In addition, the recent demonstration of fiber-based sources operating in the purely normal regime with deliverable energy per pulse exceeding 100 nJ [2, 3] have made them henceforth competitive with their bulk-based counterparts. The experimental setup of the passively mode-locked LMA fiber laser is similar to the one already reported in [2, 3]. One key cavity element in this laser is the Yb-doped air-clad photonic crystal rod-type active fiber featuring an even larger active core (~ 80 μm) with a mode-field diameter as large as 71 μm and the fiber length is 1.2 m to insure a high single-pass gain factor [4]. In the picosecond regime, the modulation depth of the saturable absorber mirror (SAM) is ~10 % and the relaxation time of more than 100 ps. When the mode-locking threshold is reached, the laser delivers a single-pulse train with a repetition rate of 10 MHz. The highest possible average output power is as high as 11 W, corresponding to a pulse energy of 1.1 μJ. The narrow line emission spectrum with the spectral bandwidth of 0.4 nm at the center wavelength of 1036.36 nm is shown in Fig. 1 (a). The laser generates clean picosecond pulses with a pulse width of 310 ps, as shown in Fig. 1 (b).

© 2009 IEEE