It's a half-year project. Leading a 5 people team, I developed a eavesdrop device prototype by sensing the interference pattern of two beams laser light. The device was developed while I was a physics undergraduate student at University of Science and Technology of China (USTC) in 2011. The simplified 3D model is shown below for demonstration.
Demo Audio (Audio information collected by the device)
The audio above was collected by my device. The sound source is a iphone2G playing musice behand a window. The laser light beam from the device shot to the glass of the window. The sound was collected remotely by decoding the reflected light.