Refining common path interferometry with a spiral phase Fourier filter

Author(s): Christian Maurer , Stefan Bernet, Monika Ritsch-Marte

Abstract:

“Recently, spiral phase filtering for isotropic edge enhancement and for optical thickness measurements of phase samples has been implemented in microscopy, using gray value images on a spatial light modulator (SLM) placed in a Fourier plane of the sample. In a common path interferometer, the light going through the central part of the helical phase hologram is overlapped with the light passing through the periphery of the phase filter. Replacing the center by a disk of uniform phase leads to pseudo-relief images, with the apparent illumination direction depending on the gray level of the central area. If one uses such images to reconstruct the optical thickness of phase objects, the reference wave through the central part ideally should have a plane wavefront. This is normally not the case, especially when the imaging setup requires a relatively large central area around the DC Fourier component. This paper shows how a direct measurement of the amplitude of the reference beam, which can be done in the given setup by simply changing the image on the SLM, can increase the accuracy of phase measurement, allowing one to determine the refractive index with a relative error below 0.6%.”

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Publication: Journal of Optics A
Issue/Year: J. Opt. A: Pure Appl. Opt. (2009) 11 094023
DOI: 10.1088/1464-4258/11/9/094023

A Review of Incoherent Digital Fresnel Holography

Author(s): Joseph Rosen, Gary Brooker, Guy Indebetouw, Natan T. Shaked

Abstract:

“We review three different methods of generating digital Fresnel holograms of 3-D real-existing objects illuminated by incoherent light. In the first method, a scanning hologram is generated by a unique scanning system in which Fresnel zone plates (FZP) are created by a homodyne rather than the common heterodyne interferometer. During the scanning, the FZP projected on the observed object is frozen rather than varied as previously. In each scanning period, the system produces an on-axis Fresnel hologram. The twin image problem is solved by a linear combination of at least three holograms taken with three FZPs with different phase values. The second hologram reviewed here is the digital incoherent modified Fresnel hologram. To calculate this hologram, multiple-viewpoint projections of the 3-D scene are acquired, and a Fresnel hologram of the 3-D scene is directly computed from these projections. This method enables to obtain digital holograms by using a simple digital camera, which operates under regular light conditions. The last digital hologram reviewed here is the Fresnel incoherent correlation hologram. In this motionless holographic technique, light is reflected from the 3-D scene, propagates through a diffractive optical element (DOE), and is recorded by a digital camera. Three holograms are recorded sequentially, each for a different phase factor of the DOE. The three holograms are superposed in the computer, such that the result is a complex-valued Fresnel hologram that does not contain a twin image. ”

Link to Publications Page

Publication: Journal of Holography and Speckle
Issue/Year: Journal of Holography and Speckle, Volume 5, Number 2, August 2009 , pp. 124-140(17)
DOI: 10.1166/jhs.2009.1006