Emmett N. Leith

Reconstructed Wavefronts and Communication Theory

A two-step imaging process discovered by Gabor involves photographing the Fresnel diffraction pattern of an object and using this recorded pattern, called a hologram, to construct an image of this object. Here, the process is described from a communication-theory viewpoint. It is shown that construction of the hologram constitutes a sequence of three well-known operations: a modulation, a frequency dispersion, and a square-law detection. In the reconstruction process, the inverse-frequency-dispersion operation is carried out. The process as normally carried out results in a reconstruction in which the signal-to-noise ratio is unity. Techniques which correct this shortcoming are described and experimentally tested. Generalized holograms are discussed, in which the hologram is other than a Fresnel diffraction pattern.

Wavefront Reconstruction with Diffused Illumination and Three-Dimensional Objects*

Holograms of transparencies have been produced in diffused light. The reconstructions are free from flaws and are of a quality comparable to pictures produced by conventional photography with incoherent light. Holograms of three-dimensional scenes have been produced by reflected light. Such holograms produce three-dimensional reconstructions having all the visual properties of the original scene: parallax between near and distant objects, a requirement to refocus the eyes when viewing objects in different parts of the scene, and a stereo effect equal to that of ordinary stereo photography.

Wavefront Reconstruction with Continuous-Tone Objects*

Holograms and high-quality reconstructions have been made by using a two-beam interferometric technique. The extraneous twin image and other interfering terms have been eliminated. Two types of objects have been used which are not suitable for the conventional wavefront reconstruction technique: objects which do not transmit a strong background wave (e.g., transparent lettering against a dark background) and continuous-tone objects.

Holographic data storage in three-dimensional media.

The holographic storage of diffraction patterns in a three-dimensional media is described from a vector viewpoint derived from the Kirchhoff diffraction integral. The sensitivity of the reconstruction to wavelength and to the orientation of the readout beam is calculated, and experimental results are given.

Microscopy by Wavefront Reconstruction

Magnification by the wavefront-reconstruction imaging method is discussed. An analysis is given of the aberrations which arise in this type of imagery. Conditions are derived which lead to aberration-free reconstructions.

Two-dimensional imaging through diffusing media using 150-fs gated electronic holography techniques

We combine 150-fs holographic gating with specifically adapted electronic holography techniques to produce transmission images of objects embedded in diffusing material. The technique captures, without the use of scanning procedures, complete two-dimensional images with 150-fs temporal resolution, thereby yielding submillimeter spatial resolution through diffusing objects several centimeters thick.

Imaging through scattering media with holography

Various holographic methods for imaging through scattering media such as biological tissue are described. The methods utilize light of either reduced spatial coherence or reduced temporal coherence.

Correction of Lens Aberrations by Means of Holograms

Holograms are made of a wavefront emerging from a lens having spherical aberration. The hologram, when used in combination with the lens, serves as a corrector plate for the lens. Experimental results are given, followed by a third-order analysis.

Space-invariant achromatic grating interferometers: theory

A general analysis of an n-grating interferometer under various conditions of illumination is presented, where n = 1,...,4. Conditions for fringe localization and effects of misalignment are given. The lesser known phenomenon of the imaging of a grating by a second grating is described from which the fringe forming capacity of multiple-grating interferometers stems; this can occur regardless of the coherence of the source.

Quasi-holographic techniques in the microwave region

Various microwave processes, including synthetic-aperture radar and linearly frequency-modulated pulse compression, are described as analogs of holography. The holographic viewpoint often leads to a new understanding and to new methods of signal processing.