We have checked whether the frequency ratio between fundamental and second-harmonic optical frequencies is exactly 1:2 by measuring the frequency difference between the second harmonics of two diode lasers and comparing it with the frequency difference of the fundamentals. We have improved the 30-year-old experimental limit on the accuracy of the 1:2 frequency ratio by 7 orders of magnitude for frequency-dependent shifts to 2.3 parts in 1013 for a KNbO3 crystal.
© 1995 Optical Society of America
R. Wynands, O. Coste, C. Rembeand, and D. Meschede, "How accurate is optical second-harmonic generation?," Opt. Lett. 20, 1095-1097 (1995)