Photographic Film Was Exposed: A high-powered laser was used as a light source to illuminate a white test target 8 mi (13 km) away. The reflected light was observed with a 48 in. (122 cm) telescope, but the image was too blurred to be meaningful. Then an effective reflector was placed beside the target and a man smoking a pipe stood in front of the target. To make a hologram, photographic film was exposed to the light gathered by the telescope.
The entire wafer is first covered with a film of photosensitive emulsion. This emulsion can be easily washed away with a solvent unless it is first hardened by exposure to ultraviolet light. A precise photographic mask, with clear and opaque patterns, is placed over the photographic emulsion. The mask contains transparent areas that cover those wafer parts that are to remain n-type, and opaque areas that cover those parts that are to become p-type and are not to be exposed to ultraviolet light.
After the mask is placed over the emulsion-covered wafer, the mask-wafer combination is exposed to ultraviolet light.
The Automatic Photograph Company in New York boasted in 1895 that they could produce 157,000 finished photographic prints in a ten-hour working day. A 3000-foot roll of bromide paper 36 inches wide was "fed under two or more negatives, then automatically pressed upward by a platen against the face of the negative, at the same instant also automatically exposed by the flashing of incandescent electric lamps above the negatives, then moved along the proper distance for a fresh section to be exposed and finally wound up on another roller."21 In a second machine the exposed paper was fed by rollers through the processing solutions.
|
|
Photography
