Chromato-axial memory effect through a forward-scattering slab

Abstract

Light propagation through scattering samples involves long optical path lengths typically resulting in short spectral correlation widths. Here, we demonstrate experimentally and theoretically a chromato-axial memory effect through volumetric forward-scattering slabs of thickness lying in the range between the scattering mean free path and the transport mean free path: a spectral shift of the impinging collimated beam results in an axial homothetic dilation of the speckle pattern over large spectral widths. The center of the homothety is shown to lie at a virtual plane located at 1/(3n) of the slab thickness L, before the output surface. These results provide new tools to blindly control wavefields through scattering samples.

Memory effect assisted imaging through multimode optical fibres

“… 17 , 40 , refocussing can be achieved by taking advantage of this symmetry and adding a quadratic ‘lensing’ phase term directly to the field that is generated by the DMD. We note this input transformation is also related to the recently reported ‘chromato-axial’ memory effect studied in other forward scattering media 41 . Therefore we actually create fields corresponding to defocussed spots at the distal facet of the fibre, which then focus onto the resolution target.…”

Local Surface Chemistry Dynamically Monitored by Quantitative Phase Microscopy

“…The core part of DIPSI is the addition of a thin diffuser between the microscope exit and the CCD sensor, at a distance d (typically 3 mm) from the sensor, leading to the formation of a random speckle‐like pattern, as described in detail elsewhere. [ 43 ] Briefly, due to the so‐called angular memory effect, [ 43,71,72 ] a tip/tilt of the incident wavefront results in a translation of the speckle pattern. Therefore, the local phase gradient can be extracted by tracking the local translation of the speckle grains.…”

Chromato-axial memory effect in step index multimode fibers

“…It has been shown experimentally that a chromatic shift induces an axial drift of a beam focused by wavefront shaping behind 1 mm-thick brain tissues, over spectral widths as large as ∼ 100 nm [27]. Theoretical modeling established that this broadband chromato-axial (χ-axial) ME is a characteristic of forward scattering media thinner than the transport mean free path [28], where the product λz (wavelength, axial plane), is specifically conserved when illuminated by a plane wave [28,29]. In essence, the χ-axial ME is due to the conservation of the transverse component of the wave-vector under spectral detuning.…”

“…Based on the cylindrical symmetry of MMF, rotational ME could be demonstrated [25,26]. Recently, the concept of ME has even been broadened to the spec-tral domain [27,28]. It has been shown experimentally that a chromatic shift induces an axial drift of a beam focused by wavefront shaping behind 1 mm-thick brain tissues, over spectral widths as large as ∼ 100 nm [27].…”

“…The χaxial ME is not only observed for an engineered focused spot, but also when coupling random light patterns to the fiber. In this case, the similarity of speckles can be observed by computing the zero-mean cross-correlation products between output speckles [28]:…”