A photoacoustic catheter includes an elongated catheter body and a housing positioned near a distal end of the elongated catheter body. A length of multimode fiber extends through the elongated catheter body and has a distal end that is beveled at about 45° relative to a longitudinal axis of the multimode fiber and is positioned in the housing. An ultrasonic transducer, electrically connected to an electrical wire extending along the elongated catheter body, is positioned within the housing. A mirror element is also positioned within the housing and includes a mirror surface beveled at about 45° relative to the longitudinal axis of the multimode fiber. The catheter is operable to deliver an optical wave through the multimode fiber and to deliver an ultrasonic wave collinearly from the housing and out of an aperture of the housing to obtain optical data and ultrasonic data within a mammalian luminal organ.