Abstract: An electro-optical ranging system is disclosed for purposes of measuring or determining the distance from a transmitting/receiving location to an object, such as a target. An electro-optical transducer, such as a laser diode, is employed which exhibits the characteristic of emitting radiant energy in the infrared region when driven into a conductive condition and also exhibits the characteristic of being in a photovoltaic condition in response to receipt of radiant energy within the wavelength of the energy emitted. The transducer is periodically driven so as to emit radiant energy, and an optical directing means, such as an optical lens system, is employed for purposes of directing emitted energy from the transducer along a path toward the target as well as for receiving energy traveling in the opposite direction from the target and directing the received energy so as to impinge upon the transducer such that the transducer is actuated to a photovoltaic condition.