25-W, continuous-wave, 629-nm solid-state laser source

We report an efficient, high-power, cw, $629-\mathrm{nm}$ laser source based on a diode-pumped Nd:YAG laser and a periodically poled lithium niobate (PPLN) frequency converter. This device integrates two separate frequency-conversion steps in a single crystal, taking advantage of the ability to fabricate PPLN with nearly arbitrary grating periods and phase-matching temperatures. This device uses a single PPLN crystal that has two grating regions in series. The first region quasi-phase matches a standard optical parametric oscillator process ($1064 \mathrm{nm}\to 1540 \mathrm{nm}+3450 \mathrm{nm}$), and the second region quasi-phase matches a sum-frequency process whereby the pump and the signal light make red light ($1064 \mathrm{nm}+1540 \mathrm{nm}\to 629 \mathrm{nm}$). Using a four-mirror ring cavity, we were able to convert 21% of the $1064-\mathrm{nm}$ pump to $629-\mathrm{nm}$ output, yielding $2.5 \mathrm{W}$ of red output with $11.8 \mathrm{W}$ of input.