We mix the emission of a femtosecond Ti:sapphire laser with the emission of a continuous wave infrared laser in a beta-barium borate crystal. Green light with a center wavelength of 527 nm and a spectral width of 2.5 nm resulting from sum frequency generation is detected. An intensity study verifies that a nonlinear χ (2) process is at the origin of the green light generation. The experimentally obtained conversion efficiency of 7 × 10 −10 is in good agreement to simple theoretical considerations.