The intensity dependent refractive index change of photochromic proteins

Abstract

We report the nonlinear refractive index behaviour of bacteriorhodopsin and photoactive yellow protein films. A Michelson interferometer with a probe and excitation beams was used in the measurements. By using this technique instead of the Z-scan we can easily separate the index change caused by photochromism and the thermal expansion. Sigmoidal index changes in the logarithmic intensity scale were observed.