Conversion of near infrared to visible light by optical mixing

Collinear 3.3913- and 0.6328-micron laser beams were mixed in LiNbO
3
to produce the sum frequency corresponding to 0.5333 microns. The laser beams were generated simultaneously in a single He-Ne laser tube. With incident powers of 4.43 and 2.75 mW at 0.63 and 3.39 microns, respectively,
3.65 \times 10^{-7}
mW were generated at 0.53 microns. The magnitude of this conversion is in satisfactory agreement with theory. Some of the characteristics of this system when viewed as an infrared detector are also given.