Abstract

We have explored and demonstrated^1,2 a new concept for comparing optical frequencies to radio frequencies. It is based on the coherent generation of an intermediate frequency f₃ = (f₁) + f₂)/2 by nonlinear processes and is shown schematically in Fig. 1. Division of the f₂−f₁ interval is achieved by phase locking the sum frequency f₁ + f₂ to the second-harmonic frequency 2f₃ with conventional servo loop techniques.

© 1991 Optical Society of America