after it has been developed

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Senior Member

In recognition holography a holographic image of an object is recorded in the usual manner, save that the laser beam is bounced off a special kind of mirror known as a focusing mirror before it is allowed to strike the unexposed film. If a second object, similar but not identical to the first, is bathed in laser light and the light is bounced off the mirror and onto the film after it has been developed, a bright point of light will appear on the film. (Holographic Universe/Michael Talbot)

Does it mean the film was developed at the time when the light struck it or it was developed later?
  • stormwreath

    Senior Member
    English - England
    Neither: it was developed earlier. The light from the second object is shone onto the film after the film has already been developed.

    Sequence of events:

    1. Take the undeveloped film.
    2. Make a holographic image of the first object.
    3. Develop the film: you now have a hologram of the first object.
    4. Project light off a second object onto the already-developed film.
    5. A bright point of light will appear on the developed film. Presumably the objective of this is to compare the first object to the second object, hence 'recognition' holography.
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