A system for detecting sound comprising a laser beam transmitter transmitting at least two parallel modulated laser beams through a medium having a measurable index of refraction, a beam termination mechanism configured to terminate the laser beams' transmission through the medium, a guide mechanism used to guide the terminated laser beam to at least one beam combiner, an envelope detector optically coupled to the beam combiner, wherein the envelope detector is configured to receive the terminated laser beam from the beam combiner, creating an angle modulated signal; a processor used to process the angle modulated signal to recover the sound.