## 3 Results and Discussion
### Power of Harmonic Comb Components  
For a pump wavelength of 1064 nm, the generated harmonics are at 3192 nm, 1596 nm, 1064 nm, 798 nm, 638.4 nm, and 532 nm. Output power from the SRO and subsequent harmonics produced are measured with a broadband thermopile detector (Coherent P10). The idler power at 3192 nm is determined after its transmission through the SHG crystal and a dichroic mirror used to block out the second harmonic and any residual pump power. The third harmonic (residual pump) is combined with the second, fourth, fifth and sixth harmonics that are collinear after their generation. A Pellin Broca prism is used to disperse these harmonics before sending each into the power meter. The harmonics power is measured as a function of the input pump power. The results are shown in Figure 3.  
**Figure 3.** The measured power of the multi-harmonic optical comb after Pellin Broca prism and the dichroic mirror after idler SHG in Figure 1. Here, (**a**) shows the power of the fundamental wave (idler), the 2 nd harmonic wave (signal), the 3 rd harmonic wave (residual pump power), and the 4 th harmonic wave which were generated from the frequency divided-by-three SRO and the intracavity second harmonic generation for the 4 th harmonic wave; (**b**) shows the power of 5 th harmonic wave and the 6 th harmonic wave. The 5 th harmonic wave and the 6 th harmonic wave are generated from single pass sum frequency generation and second harmonic generation, respectively.  
Figure 3a shows the power of the fundamental wave (idler), the 2 nd harmonic wave (signal), the 3 rd harmonic wave (residual pump power), and the 4 th harmonic wave in the multi-harmonic opticalcomb. The SRO's lasing threshold is at 6 W. This relatively high threshold is because the length of the SRO nonlinear crystal adopted in this experiment is shorter than used in previous experiments, and the insertion loss from the etalon and the intracavity SHG crystal. Without these extra optics, the SRO threshold drops to about 2 W. The maximum fundamental wave (idler), and the 2 nd harmonic wave (signal) power are 1.64 W and 0.77 W, respectively at an input pump power of 14 W. The residual pump power (the 3 rd harmonic wave) at this input is 3.9 W. For an output coupling of 0.6% the estimated circulating signal power in the cavity is as much as 128 W. This accounts for a respectable cw SHG conversion of the signal to the 4 th harmonic which is measured to be 0.78 W without correcting for losses. The 5 th harmonic and the 6 th harmonic are obtained by single pass wavelength mixing. Figure 3b indicates the maximum powers obtained of the 5 th harmonic wave and the 6 th harmonic wave are 166 mW and 114 mW, respectively.  
The power achieved for the frequency division-by-three SRO is at least ten times higher than previously reported in the literature [17]. This is the first time a cw harmonic comb of up to six harmonics has been reported. The total harmonic comb power of 7.4 W is unprecedented. High cw power is needed for effective phase and amplitude management of the comb components in waveform synthesis [19] and its subsequent applications. The multiwatt comb power that has been achieved is expected to be sufficient for this purpose.