Thin films are critical components in a wide range of multilayer microelectronic and optical devices, but the size scales and dissimilar nature of the constituents present challenges with regard to thermomechanical integrity and reliability. A particular challenge is the design and implementation of test procedures that measure thin film interface properties. In the current work, laser induced stress waves are used to characterize intrinsic interfacial strength of thin films under mixed-mode conditions. Laser pulse absorption generates high amplitude, short duration stress wave pulses that can be used to load the interface between a film and a substrate. Gupta and co-workers have reported extensively on a laser spallation experiment to determine the intrinsic tensile strength of planar interfaces. We explore the use of laser pulse induced shear waves to obtain a range of mixed-mode and pure shear failures of thin film interfaces. The laser-induced compression pulse is allowed to mode convert at an oblique surface, and the resulting shear wave to impinge upon the interface to be tested. A careful series of experiments and analysis is carried out for development of the mixed-mode loading method. Interfacial strengths and failure modes obtained for Al films loaded in pure shear and mixed mode are compared with those obtained for the same films loaded by a tensile wave.