Apparatus for sensing ultrasonic waves by optical means

An apparatus for sensing by optical interference the deformation of a workpiece surface resulting from acoustic energy present in the workpiece comprising:

• a laser disposed for directing its beam of light upon a surface portion of the workpiece for sensing such deformation, said surface portion reflecting a portion of the incident light;
• light control means disposed for controlling the intensity of the light incident upon said surface portion;
• an optical interferometer disposed for receiving the light reflected at said surface portion;
• first photoelectric means operatively associated with said interferometer for receiving the light from said interferometer and providing a first electrical output signal commensurate with the deformation of the surface portion to an evaluation signal;
• optical beam splitting means cooperatively associated with said interferometer for providing an optical signal which is complementary with respect to the light received by said first photoelectric means;
• second photoelectric means coupled for receiving said optical signal and providing a second electrical output signal commensurate with said complementary optical signal;
• summing means coupled for receiving said first and said second electrical output signal and providing a third electrical output signal commensurate with the sum of said first and second electrical output signals, and
• control means coupled for receiving said third electrical output signal and a set value signal and providing a control signal to said light control means for adjusting said laser beam of light incident upon said workpiece in response to any deviation of said third electrical output signal relative to said set value signal.