30-THz upconversion of an AlGaAs diode laser with AgGaS(2): bridging the several-terahertz frequency gap in the near infrared

We report as much as 6-micro W upconverted cw radiation at lambda = 778 nm from the sum-frequency mixing of a 50-mW diode laser at lambda = 842 nm and a 200-mW CO(2) laser at lambda = 10.2 microm by use of a 15-mm-long silver thiogallate crystal. This nonlinear material provides a convenient connection between IR and visible/near-IR optical standards. We describe simple frequency chains based on this upconversion process that permit the absolute frequency measurement of many visible or near-IR possible standards at the 10(-12) accuracy level. Transposition of terahertz-scale frequency-difference measurements from the near IR to the 10-microm domain is also proposed.