Pulsed laser interferometry

A system has been developed which is capable of interferometrically measuring optical path length changes, with high spatial and temporal resolutions. The capability to freeze fast motion is provided by the pulse length of the laser, the frame rate is determined by the laser and camera, and the spatial resolution is determined by the camera and data resorder. The system has been applied to measuring the optical disturbance through an aerocurtain, a shock wave produced by a supersonic projectile, thermodynamic gas flow, and membrane mirror surfaces. The choice of interferometer type is determined by environmental and optical considerations such as expected jitter and magnitude of aberrations. The phase at each point is determined by taking intensity values of the interference pattern at three sequential pixels, labled A, B, and C, after introducing large amount of tilt fringes and applying the spatial phase shifting algorithm: 0 = arctan((C-B)/(A-B)}. The current system uses 100 ns pulse at any desired repetition rate or a 10 ns pulse at 30 Hz. The camera and recorder provide a resolution of 510x480 pixels at 30 Hz or 248x192 pixels at 2000 Hz.