Conventional ultrasonic imaging techniques, including holographic, have high resolution in angle, but relatively poor resolution in range, because resolution in range is obtained only by use of selective focus or parallax, which is useful only with small focal ratio. The paper presents the principle and some experimental results of new ultrasonic imaging techniques that use a linear FM ultrasonic pulse and a pulse of light. This method gives high resolution both in angle and in range; it may be considered to be an application of pulse-compression techniques, used in chirp radar, to ultrasonic imaging, but it has image-forming as well as range-discriminating capability.
TAKUSO SATO, MITSUHIRO UEDA, and HISASHI TADA, "Ultrasonic Imaging System by Using Optical Pulse Compression," J. Opt. Soc. Am. 62, 668-671 (1972)