Submersible holographic microscope

A low-cost, 20-kg device has been developed that allows scientists to form three-dimensional images of the trajectories of tiny marine organisms in their natural environment. Scientists at Dalhousie University in Halifax, Canada, used a simple hologram arrangement: Laser light is focused onto a pinhole aperture in the laser’s watertight housing. The spherical waves that emanate from that point source then illuminate a sample of seawater, scatter from objects in the water, and recombine—at the photosensitive area of a CCD camera housed in a separate container—with the reference beam that went straight through the seawater without scattering. The digital holograms are then reconstructed into images of the objects. Shown here is a marine ciliate Favella, imaged with a 0.2-ms exposure at a depth of 10 m as the animal swam from right to left at 2.1 mm/s. Holograms with 1024 × 1024 pixels can be recorded at up to 10...