Interference Imaging

Holography is "lensless photography" in which an image is captured not as an image focused on film, but as an interference pattern at the film.

The Transmission Hologram

The coherent light from the laser is split to form an object beam and a reference beam. The light from the illuminated object and the reference beam form an interference pattern on the film. This pattern (hologram) contains the information about the object which can then be viewed as a three dimensional image. 激光产生的相干光被分裂成一个物光束和一个参考光束。物光束与参考光束在胶片上形成干涉图样。这个图样（全息图）包含了关于物体的信息，之后可以被观看成一个三维图像。

Viewing a Transmission Hologram

Holography is lensless photography. The image is captured in the interference pattern on the film, and the image can be reconstructed for viewing by shining the coherent light of a laser on the hologram. The eye is focused behind the film to see the image suspended in space. It shows the unique characteristics of holographic images.

The diverged laser beam should be placed in the same orientation with respect to the film as the reference beam which was used to make the hologram. Then the image will be seen in the same position as the original object with respect to the film. It is as if the light from the object was frozen in the film, and then continues to your eye when reconstructed with the laser light.