Fig. 1. Nonlinear absorption measurement of the MWCNT SA. Insets (a) The Raman spectrum and (b) the linear absorption of the SA.

Fig. 2. Schematic diagram of a passive Q-switched TFFL.

Fig. 3. Characteristics of Q-switched output pulses at a pump power of 99.4 mW. (a) The optical spectrum (λ=1486.4  nm) and pulse train of the Q-switching operation [inset (a) and (b)] and (b) the RF spectrum at the fundamental frequency (f0=32.1  kHz) wideband RFSA spectrum [inset (a)] and stability of the Q-switching operation for 1 h [inset (b)].

Fig. 4. (Color online) Trends of (a) the repetition rate and pulse width and (b) the average output power and pulse energy against the increasing pump power and the CW output power as a function of pump power (inset).