In 2025, MxV Rail collaborated with Modality, Inc. to design and develop a laser air-coupled ultrasound testing (LACUT) technique for detecting rail base defects that are difficult to find with current techniques. Two rail samples with a total of eight different sized electrical discharge machined (EDM) notches were considered for this study. These notches were cut both fully and partially through the base flange thickness between the top and bottom surfaces of the rail base flange corners. Two measurement approaches were considered in the laboratory settings and compared in this study. In the first configuration, the laser source was placed between two transducers, and in the second configuration, the laser source was place outside both transducers. Both configurations were equally able to detect EDM notches. Both approaches produced good signal-to-noise ratio (SNR) between a defect/no-defect condition, but detection sensitivity decreased with increased distance between the generation point and the position…