Off-axis configuration In the off-axis configuration, a small angle between the reference and the object beams is used to prevent overlapping of the cross-beating contributions between the object and reference optical fields with the self-beating contributions of these fields. These discoveries were made by
Emmett Leith and
Juris Upatnieks for analog holography, and subsequently adapted to digital holography. In this configuration, only a single recorded digital interferogram is required for image reconstruction. Yet, this configuration can also be used in conjunction with temporal modulation methods, such as phase-shifting and frequency-shifting for high sensitivity measurements in low light.
Phase-shifting holography The phase-shifting (or phase-stepped) digital holography process entails capturing multiple
interferograms that each indicate the optical phase relationships between light returned from all points on the illuminated object and a controlled reference beam of light. The optical phase of the reference beam is shifted from one sampled interferogram to the next. From a linear combination of these interferograms, complex-valued holograms are formed. These holograms contain amplitude and phase information of the optical radiation diffracted by the object, in the sensor plane.
Frequency-shifting holography Through the use of electro-optic modulators (Pockel cells) or acousto-optic modulators (Bragg cells), the reference laser beam can be frequency-shifted by a tunable quantity. This enables
optical heterodyne detection, a frequency-conversion process aimed at shifting a given radiofrequency optical signal component in the sensor's temporal bandwidth. Frequency-shifted holograms can be used for narrowband
laser Doppler imaging.
Multiplexing of holograms Addressing simultaneously distinct domains of the temporal and spatial bandwidth of holograms was performed with success for angular, wavelength, Super-localization of particles can be achieved by adopting an optics/data-processing co-design scheme.
Optical Sectioning in Digital Holography Optical sectioning, also known as sectional image reconstruction, is the process of recovering a planar image at a particular axial depth from a three-dimensional digital hologram. Various mathematical techniques have been used to solve this problem, with inverse imaging among the most versatile.
Extending Depth-of-Focus by Digital Holography in Microscopy By using the 3D imaging capability of Digital Holography in amplitude and phase it is possible to extend the depth of focus in microscopy.
Combining of holograms and interferometric microscopy The digital analysis of a set of holograms recorded from different directions or with different direction of the reference wave allows the numerical emulation of an objective with large
numerical aperture, leading to corresponding enhancement of the resolution.{{cite journal == See also ==