Fig. 5
a Optical spectrum of fundamental mode-locking with \(\nu ={-5.55\times {10}^{-7}\mathrm{ W}}^{-2}/\mathrm{m}, {P}_{sat,g}=78\ \mathrm{mW}\). b Optical spectra of 2nd harmonic mode-locking with \(\nu ={-5.55\times {10}^{-7}\mathrm{ W}}^{-2}/\mathrm{m},{P}_{sat,g}=141\ \mathrm{mW},\) and c that with \({P}_{sat,g}=165\ \mathrm{mW}\). The inset in b shows the optical power profile in the laser cavity evolving to 2nd harmonic mode-locking