Abstract

It is now firmly established that during thermal poling of glass a thin depletion region is formed under the anodic interface and it is in this region that the induced second order nonlinearity (⁽²⁾) is concentrated. Many experiments also indicate that the ⁽²⁾ is created via the intrinsic material ⁽³⁾ and the frozen-in electric field. One of the most relevant quantities in understanding the poling process is the nonlinear depth (h) which is usually measured using the Makers Fringe Technique (MFT), extensively described in [1] and preferred to destructive chemical etching methods. However, as has already been pointed out [2], the MFT can only attain a rather limited internal angle (40° in SiO₂) and therefore can distinguish between different film depths only if they are larger than a certain value (15 m @ 1.064 m pump wavelength in SiO₂) which depends on the bound-and free-wave phase mismatch, k. A variation of the MFT has been proposed in [2] to overcome this limitation but it involves placing the sample between glass prisms and using index-matching fluid - a not always feasible alternative. We propose a two-noncollinear beam MFT that can measure nonlinear depths down to 2 m with sub- m resolution in glass and can be readily applied to second-order nonlinear films made of any other material.

© 2000 IEEE