Experimental generation of an optical field with arbitrary spatial coherence properties

Abstract

We describe an experimental technique to generate a quasi-monochromatic field with any arbitrary spatial coherence properties that can be described by the cross-spectral density function, W (r 1 , r 2 ). This is done by using a dynamic binary amplitude grating generated by a digital micromirror device (DMD) to rapidly alternate between a set of coherent fields, creating an incoherent mix of modes that represent the coherent mode decomposition of the desired W (r 1 , r 2 ). This method was then demonstrated experimentally by interfering two plane waves and then spatially varying the coherence between them. It is then shown that this creates an interference pattern between the two beams whose fringe visibility varies spatially in an arbitrary and prescribed way.

Pseudo-Schell model sources

“…In both cases, the physical meaning of the above expansion is that a partially coherent source can be thought of as the superposition of a set of mutually uncorrelated, perfectly coherent, and suitably weighted fields. Of course, this also represents a way to physically synthesize partially coherent source [19,22,23,26,40,63], especially when they are not of the Schell-model type [6,44,45]. The superposition usually involves an infinite number of coherent fields but for practical applications a finite number is often enough for a good representation of the CSD function [27,44].…”

Besinc Pseudo-Schell Model Sources with Circular Coherence

“…When a Laguerre-Gaussian intensity at the source plane is considered (see Equation (9)), a pseudo-modal expansion [27] of the CSD has been found. Then, these kinds of sources can be synthesized by superposing a large enough number of pseudo-modes [32,33]. Peculiar behavior of the intensity profile with the propagation distance has been found: the profile becomes sharper and the maximum intensity is reached after a propagation distance from the source plane, the latter corresponding to the waist.…”

“…However, for values of the ratio δ c /w 0 lower than, approximately, 1 (2) for m = 0 (m = 1), the first pseudo-eigenvalue is not the highest one, and the contribution of higher-order modes becomes more and more significant for decreasing values of δ c /w 0 . From Figures 3 and 4, it can be concluded that the proposed pseudo-Schell model sources with circular coherence (Equations (3) and (7)) can be synthesized (with the desired precision) just by superposing a sufficiently large number of pseudo-modes with appropriate weights [32,33].…”

Spatial coherence modulation using plane waves generated with a digital micromirror device

“…Therefore, the condition of a switching time τs much faster than the integration time τi of the detector must be fulfilled. Additionally, to ensure a stochastic superposition, avoiding time correlation between states, switching time must be larger than the coherence time τc of the light source [21]. These sampling conditions can be summarized as…”

“…On the other hand, DMDs have been applied for modulating spatial coherence by means of the superposition of optical modes generated by binary phase and amplitude holograms [21]. However, there was no measurement of spatial coherence or any property to distinguish between the blurring due to spatial coherence from the blurring produced in the holographic reconstruction of a blur object.…”