Abstract Depth profiles of double layer biological samples, obtained by photoacoustic spectroscopy, have been studied using the phase-resolved method. The application of the method was demonstrated by insulating out the spectra of the cuticle and the pigment layers of a lettuce leaf. Using this method, we were able to monitor the phase shift between the cuticle and the pigment layers as a function of the time elapsed after herbicide spraying. The temporal changes occurring in lettuce leaves under the action of dehydration were also investigated.
