arXiv subjects

Bernard Gorzkowski

Publications and source records attributed to Bernard Gorzkowski.

4 recordsLinked to original sources

arXiv2024

Low Photon Number Non-Invasive Imaging Through Time-Varying Diffusers

Optical imaging plays a crucial role in advancing science and technology, enabling applications in fields ranging from biomedicine to astronomy. However, imaging through scattering media such as biological tissues, fog, or turbulent atmosphere remains a major challenge. Light scattering and absorption in such media make imaging challenging; in the case of time-varying scatterers and low light regime imaging of incoherent objects has not been demonstrated so far. We present the first demonstration of such non-invasive imaging of dim objects hidden behind dynamic scattering layers, obtaining robust reconstruction even at extremely low photon counts per frame. We achieve this by developing a new data-processing approach. In our experiment, we utilize a photon number resolving camera to capture a sequence of frames, containing on average, fewer than one photon per pixel. We validate our approach in microscopy, where we reconstruct images of biological samples stained with standard fluorescent dyes. Beyond microscopy, our approach can be applied in different imaging techniques, such as endoscopy based on multicore fibers or ground-based astronomical observations.

physics.optics↗

arXiv2024

Canonical and Poynting currents in propagation and diffraction of structured light: tutorial

Local propagation and energy flux in structured optical fields is often associated with the Poynting vector. However, the local phase gradient (i.e., local wavevector) in monochromatic fields in free space is described by another fundamental quantity: the canonical momentum density. The distributions of the Poynting and canonical momentum densities can differ significantly from each other in structured fields. We examine the role of these quantities in the propagation and diffraction of structured optical fields, exemplified by various circularly-polarized vortex beams carrying orbital angular momentum. We describe the canonical and Poynting momentum distributions in such beams, experimentally measure the local transverse momentum density by Shack-Hartmann wavefront sensor, and investigate fine features of the diffraction of various vortex beams on a knife-edge aperture. In all cases, the measured local momentum density and local beam evolution are consistent with the canonical momentum distribution rather than the Poynting vector. Furthermore, we introduce the local angular velocity in vortex beams and determine the universal integral $\pi$ angle of azimuthal rotation in an arbitrary (yet circularly-symmetric) propagating and diffracting vortex beam. Finally, we discuss the "supermomentum" and "backflow" effects; both of these phenomena are examples of superoscillations and are related to the properties of the canonical momentum. Our results reveal the profound role of the canonical momentum in the evolution of light and demonstrate the importance of distinguishing between it and the Poynting vector in structured light.

physics.optics↗

arXiv2023

Azimuthal backflow in light carrying orbital angular momentum

M.V. Berry's work [J. Phys. A: Math. Theor. 43, 415302 (2010)] highlighted the correspondence between backflow in quantum mechanics and superoscillations in waves. Superoscillations refer to situations where the local oscillation of a superposition is faster than its fastest Fourier component. This concept has been used to demonstrate backflow in transverse linear momentum for optical waves. In this work, we examine the interference of classical light carrying only negative orbital angular momentum and observe in the dark fringes of such an interference, positive local orbital angular momentum. This finding may have implications for the studies of light-matter interaction and represents a step towards observing quantum backflow in two dimensions.

physics.optics↗

arXiv2022

Demonstrating backflow in classical two beams' interference

The well-known interference pattern of bright and dark fringes was first observed for light beams back in 1801 by Thomas Young. The maximum visibility fringes occur when the irradiance of the two beams is equal, and as the ratio of the beam intensities deviates from unity, fringe visibility decreases. An interesting outcome that might not be entirely intuitive, however, is that the wavefront of such unequal amplitude beams' superposition will exhibit a wavy behavior. In this work, we experimentally observe the backflow phenomenon within this wavy wavefront. Backflow appears in both optics (retro-propagating light) and in quantum mechanics where a local phase gradient is not present within the spectrum of the system. It has become an interesting subject for applications as it is closely related to superoscillations whose features are used in super resolution imaging and in a particle's path manipulations. The first successful attempt to observe backflow was made only recently in an assembly of optical fields, by synthesizing their wavefront in a complex manner. Yet, backflow is perceived as hard to detect. Here, by utilizing interference in its most basic form, we reveal that backflow in optical fields is robust and surprisingly common, more than it was previously thought to be.

physics.optics↗