Fig. 1. Schematic of the Yb:KLuW WG laser for SWCNT-SA mode-locking. The optical microscope image (red box) represents the input channel of the fs-DLW Yb:KLuW WG.

Fig. 2. Oscilloscope traces of the mode-locked pulses at repetition frequencies of (a), (b) 2.27 GHz, (c), (d) 2.69 GHz, and (e), (f) 3.55 GHz in different time spans of 10 μs and 7 ns.

Fig. 3. Radio-frequency spectra of the mode-locked pulses at repetition rates of (a), (b) 2.27 GHz, (c), (d) 2.69 GHz, and (e), (f) 3.55 GHz. (a), (c), and (e) show the harmonics of the mode-locked frequency in a wide frequency span, while (b), (d), and (f) show the fundamental beat note in a 2-MHz-frequency span.

Fig. 4. Autocorrelation traces and their sech2 fit (red curves) of the mode-locked pulses at repetition rates of (a) 2.27 GHz, (b) 2.69 GHz, and (c) 3.55 GHz at the maximum power.

Fig. 5. (a) 3.55-GHz mode-locked laser spectrum (inset: laser beam profile) at the maximum power and (b) average output powers versus absorbed pump powers for the CW and the 3.55-GHz mode-locked operation.