A camera to record underwater particles using simultaneous in-line and off-axis hologrammetry and its associated replay facility

Summary form only given. The HOLOMAR collaboration have designed and built an underwater holographic camera specifically designed to record marine plankton to a maximum depth of 100 m below sea level. The camera records holograms using both the in-line and the off-axis techniques simultaneously. The laser is a specially designed frequency doubled Nd-YAG laser, using a passive Q-switch and LBO doubler. It produces a single pulse with an energy of 700 mJ and duration of less than 10 ns. The oscillator-amplifier design results in a single longitudinal mode with a measured coherence length of over 2 m. Considerable care was taken in the optical design to minimise the effects of distortion arising from the change in refractive index. The computer controlled, fully automated replay machine and image processing and analysis systems allow large amounts of data to be extracted from the holograms without manual intervention.