Abstract

During the last decades a phase locking phenomenon has been observed for second harmonic (SH) generation but only recently it was recognized as such in systematic studies [1]. The general solution of the SHG from a linear/nonlinear boundary layer is composed of one reflected and two forward propagating components. One of these forward components displays a k-vector that is a solution of the homogeneous wave equation (i.e. the expected SH wave vector). The second component displays a different k-vector, solution of the inhomogeneous wave equation -the phase locked (PL) component- equal to twice the pump wave vector. The key result is that the PL SH component effectively “reads” the value of the refractive index of the fundamental frequency (FF). Ref.[2] demonstrates that the PL SH signal is transmitted through a thick sample, even though the SH was tuned above the absorption band edge. This means that the imaginary part of n(ω) (i.e. the absorption coefficient) is also impressed on the PL SH component. A sufficient condition for the effect to occur is that the pump be tuned to a region of optical transparency.

© 2009 IEEE