The in-guide pump and probe analysis illustrated in this paper is useful for the characterisation of photoinduced phenomena in thin films that are already part of an optoelectronic device. Measurements were carried on a-Si:H∕ZnO waveguiding multilayers designed for the telecommunication wavelength of 1.55μm. Because of the waveguiding geometry, the probe beam propagates along the film under test, a configuration that allows two advantages. First, the underlying layers do not affect the acquisition, and therefore the use of a transparent substrate is not necessary. Second, a longer region is available for the interaction between the pump and probe beams with respect to normal incidence probe beam setups, a characteristic conferring a high sensitivity to the technique. An analysis of the experimental data is proposed to extract information on the material, independent, e.g., of the device geometry. As an …