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Why can even slight movement spoil a continuous-wave laser hologram?

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hologram graphic — holography Figure 1: Gabor's original method for creating holograms.

In continuous-wave (CW) laser holography, the creation of a hologram relies on recording a stable interference pattern on a photographic plate. This pattern is formed by the interaction of two coherent light beams: a reference beam and a beam reflected from the object.123

These interference fringes consist of alternating light and dark areas created by the phase relationship between the two beams. Because these fringes are extremely fine and close-packed, even a microscopic shift in the position of the object or the optical components during the exposure will cause the interference pattern to move or blur across the photographic plate.14

If the object moves by even a fraction of a wavelength of the laser light, the phase relationship between the beams is disrupted, causing the fringes to wash out or shift. This destroys the precise phase and amplitude information required to reconstruct the three-dimensional image, effectively spoiling the hologram. Consequently, achieving high-quality results with CW lasers requires exceptional mechanical stability throughout the entire exposure process.134