Diffractive optical element for improving the Z-scan technique sensitivity

One of the most Successful experimental technique for determining nonlinear properties of optical materials is the Z-scan technique. Interaction between a high intensity beam with a Kerr medium gives rise to a lensing effect that implies focusing or defocusing of the beam which is transformed into transmittance variations of a diaphragm set in the far-field. In other words, one can consider Z-scan technique as a diagnostic of beam divergence variations and its ultimate sensitivity depends on the smallest transmittance change that can be measured. In this paper we propose a new technique allowing to multiply the sensitivity of the Z-scan technique by a factor greater than one hundred. The basic idea is to "amplify" the divergence variation, by a Diffractive Optical Element.