Fig. 1. Nonlinear reflection measurement of the CNT-SAM at 1.5 μm.

Fig. 2. (a) Schematic and (b) photograph of 550-MHz femtosecond Cr:YAG laser. Cr:YAG: 20-mm-long Cr:YAG gain crystal; M1, M2: HR-coated concave mirrors with ROC=−50  mm; CM1: HR-coated concave GTI mirror with ROC=−100  mm and with one bounce dispersion of −225  fs2; CM2: HR-coated plane GTI mirror with one bounce dispersion of −375  fs2; CNT-SAM : carbon nanotube saturable absorber mirror; OC: output coupler with 0.5% or 0.8% transmission.

Fig. 3. Average output power versus incident pump power in the femtosecond mode-locked regime, and beam profile of second harmonic generation of mode-locked pulses (inset).

Fig. 4. Autocorrelation trace (left) and the corresponding laser spectrum (right).

Fig. 5. RF spectra at the fundamental beat note and in a 7.5 GHz span (inset).

Fig. 6. Mode-locked laser spectra measured at different humidity conditions.