arXiv subjects

Eitan Edrei

Publications and source records attributed to Eitan Edrei.

4 recordsLinked to original sources

arXiv2018

Focusing through scattering medium: a fundamental trade-off between speckle size and intensity enhancement

Focusing light through highly scattering materials by modifying the phase profile of the illuminating beam has attracted a great deal of attention in the past decade paving the way towards novel applications. Here we discovered a tradeoff between two seemingly independent quantities of critical importance in the focusing process: the size of the focal point obtained behind a scattering medium and the maximum achievable brightness of such focal point. We theoretically derive and experimentally demonstrate the fundamental limits of intensity enhancement of the focal point and relate them to the intrinsic properties of the scattering phenomenon. We demonstrate that the intensity enhancement limitation becomes dominant when the focusing plane gets closer to the scattering layer thus limiting the ability to obtain tight focusing at high contrast, which has direct relevance for the many applications exploring scattering materials as a platform for high resolution focusing and imaging

physics.optics↗

arXiv2018

Sensor-less adaptive optics for Brillouin micro-spectroscopy

Brillouin spectroscopy is a powerful optical technique for viscoelastic characterization of samples without contact. However, like all optical systems, Brillouin spectroscopy performances are degraded by optical aberrations, and have therefore been limited to homogenous transparent samples. To correct for aberrations, adaptive optics (AO) methods have been previously integrated into a variety of optical modalities ranging from ground-based telescopes to super-resolution microscopes. In this work, we developed an adaptive optics configuration designed for Brillouin scattering spectral analysis. Our configuration doesn't require direct wave-front sensing and the injection of a 'guide-star'; hence, it can be implemented without the need for sample pre-treatment. We used our AO-Brillouin spectrometer in aberrated phantoms and biological samples; consistent with previous AO systems, we demonstrate effective correction of optical aberrations yielding 2.5-fold enhancement in Brillouin signal strength and 1.4-fold improvement in axial resolution.

physics.optics↗

arXiv2018

Diffraction-limited plenoptic imaging with correlated light

Traditional optical imaging faces an unavoidable trade-off between resolution and depth of field (DOF). To increase resolution, high numerical apertures (NA) are needed, but the associated large angular uncertainty results in a limited range of depths that can be put in sharp focus. Plenoptic imaging was introduced a few years ago to remedy this trade off. To this aim, plenoptic imaging reconstructs the path of light rays from the lens to the sensor. However, the improvement offered by standard plenoptic imaging is practical and not fundamental: the increased DOF leads to a proportional reduction of the resolution well above the diffraction limit imposed by the lens NA. In this paper, we demonstrate that correlation measurements enable pushing plenoptic imaging to its fundamental limits of both resolution and DOF. Namely, we demonstrate to maintain the imaging resolution at the diffraction limit while increasing the depth of field by a factor of 7. Our results represent the theoretical and experimental basis for the effective development of the promising applications of plenoptic imaging.

quant-ph↗

arXiv2017

Integration of spectral coronagraphy within VIPA-based spectrometers for high extinction Brillouin imaging

VIPA-based spectrometers have enabled rapid Brillouin spectrum measurements and current designs of multi-stage VIPA spectrometers offer enough spectral extinction to probe transparent tissue, cells and biomaterials. However, in highly scattering media or in the presence of strong back-reflections, such as at interfaces between materials of different refractive indices, VIPA-based Brillouin spectral measurements are limited. While several approaches to address this issue have recently been pursued, important challenges remain. Here we have adapted the design of coronagraphs used for exosolar planet imaging to the spectral domain and integrated it in a double-stage VIPA spectrometer. We demonstrate that this yields an increase in extinction up to 20dB, with nearly no added insertion loss. The power of this improvement is vividly demonstrated by Brillouin imaging close to reflecting interfaces without need of index matching or sample tilting

physics.ins-det↗