Reflection and transmission of light in multilayers perturbed by picosecond strain pulse propagation

We derive analytical formulas for the modulation of the reflectance and transmittance of light normally incident on a multilayer thin-film structure whose refractive indices are perturbed by an ultrashort optical pulse. The formulas, expressed in compact form, should prove useful for analysis of a wide range of ultrashort time-scale experiments on multilayers as well as longer time-scale photoacoustic and photothermal experiments based on optical probing. We demonstrate our method by the analysis of the modulated reflectance variation of a SiO2/Cr structure in which picosecond acoustic pulses have been optically excited.