Computer-generated holography

The term "computer-generated holography" has become used to denote the whole process chain of synthetically preparing holographic light wavefronts suitable for observation.

[2][3] If holographic data of existing objects is generated optically and recorded and processed digitally, and subsequently displayed, this is termed CGH as well.

Holography is a technique originally invented by Hungarian physicist Dennis Gabor (1900–1979) to improve the resolving power on electron microscopes.

CGH as defined in the introduction has broadly three tasks: Note that it is not always justified to make a strict distinction between these steps; however it helps the discussion to structure it in this way.

[4] Unfortunately, the researchers soon realized that there are noticeable lower and upper bounds in terms of computational speed and image quality and fidelity respectively.

The Fourier transformation concept was first introduced by Byron R. Brown and Adolf W. Lohmann[4] with the detour phase method leading to cell oriented holograms.

Calculation of the light propagation from three-dimensional objects is performed according to the usual parabolic approximation to the Fresnel-Kirchhoff diffraction integral.

The wavefront to be reconstructed by the hologram is, therefore, the superposition of the Fourier transforms of each object plane in depth, modified by a quadratic phase factor.

This concept has been first reported by Waters[16] whose major assumption originated with Rogers[17] who recognized that a Fresnel zone plate could be considered a special case of the hologram proposed by Gabor.

Once it is known what the scattered wavefront of the object looks like or how it may be computed, it must be fixed on a spatial light modulator (SLM), abusing this term to include not only LCD displays or similar devices, but also films and masks.

An ideal display for computer generated holograms would consist of pixels smaller than a wavelength of light with adjustable phase and brightness.

Currently, several companies and university departments are researching on the field of CGH devices: Recently computer-generated holography has been extended in its usage beyond light optics, and applied in generating structured electron wavefunctions with a desired amplitude and phase profile.