The transient reflecting grating (TRG) technique was applied to evaluate both nitrogen‐ion‐implanted and nonimplanted thin‐film coatings (thickness: 40 nm) of diamondlike carbon (DLC) on metallic multilayered substrates. Different TRG responses corresponding to the different nitrogen ion doses were observed. Hypersonic surface wave velocities as well as the thermal diffusivities were obtained with a variety of grating spacings. Effective elastic moduli (Young’s moduli) for the DLC coatings were given by using a theoretical treatment with a model. Nitrogen ion implantation hardened the DLC coating. ©1995 American Institute of Physics.