Resonant, continuous wave, sum frequency mixing of two Nd3+ lasers in periodically poled lithium niobate

,., present a method of generating coherent radiation in the orange to red spectral region from a singly resonant sum frequency mixer. The mixer consists of a temperature tuned 6 mm periodically poled lithium niobate nonlinear crystal inside a high finesse 1080 nm Nd :YAP laser. The nonlinear crystal is seeded by a 1444 nm Nd :YAG laser to generate radiation at 618 nm. At 670 mW seeding power of 1444 nm radiation, up to 186 mW of continuous wave radiation at 618 nm were generated, equal to 28% conversion. A beam quality of M-2 = 1.1 of the 618 nm radiation and a temperature tuning bandwidth of 7.7 K were measured. Momentarily, the output power of this mixer is limited by beam degradation of the 1080 nm Nd :YAP laser at high pump powers, probably induced by absorption and photo refractive effects in lithium niobate. In a second approach, the intracavity laser and the seeding laser were exchanged. At 2.8 W seeding power of 1080 nm radiation, 380 mW of coherent radiation at 618 nm were generated, equal to 13% conversion. A beam quality of M-2 < 1.8 and a temperature tuning bandwidth of Delta T = 8.4 K for the 618 nm radiation were measured. Unfortunately due to high nonlinear intracavity losses, relaxation oscillations of the 1444 nm Nd : YAG laser around 50 kHz were observed above a power of 1.3 W of seeding radiation at 1080 nm, generating up to 100% modulated red output.