Abstract: A laser beam stop is contructed having a uniquely designed cell filled with solution or suspension of an absorbing species chosen to absorb the wavelength of light emitted by the laser. The position and strength of the laser beam are indicated by the strength and depth of penetration of the fluorescence excited by the laser.

Abstract: A process is disclosed for making an achromatic hologram which is adapted to be reconstructed with white light and which is recorded on a photographic record carrier by means of an object beam and a reference beam of coherent monochromatic light in an operation in which the object beam and a reference beam of coherent monochromatic light in an operation in which the object beam passes through an image-forming optical element between the object and the recording material. The image forming element has a large relative aperture. When the first hologram has been recorded on the record carrier a reference beam is projected in a direction which is opposite to the direction of the reference beam used to record the first hologram and is thus used to reconstruct the object wave from the first hologram.