Multilevel Spiral Axicon for High-Order Bessel-Gauss Beams Generation.

This paper presents an efficient method to generate high-order Bessel-Gauss beams carrying orbital angular momentum (OAM) by using a thin and compact optical element such as a multilevel spiral axicon. This approach represents an excellent alternative for diffraction-free OAM beam generation instead of complex methods based on a doublet formed by a physical spiral phase plate and zero-order axicon, phase holograms loaded on spatial light modulators (SLMs), or the interferometric method. Here, we present the fabrication process for axicons with 16 and 32 levels, characterized by high mode conversion efficiency and good transmission for visible light (λ = 633 nm wavelength). The Bessel vortex states generated with the proposed diffractive optical elements (DOEs) can be exploited as a very useful resource for optical and quantum communication in free-space channels or in optical fibers.

Automated imaging, identification, and counting of similar cells from digital hologram reconstructions.

This paper presents our method, which simultaneously combines automatic imaging, identification, and counting with the acquisition of morphological information for at least 1000 blood cells from several three-dimensional images of the same sample. We started with seeking parameters to differentiate between red blood cells that are similar but different with respect to their development stage, i.e., mature or immature. We highlight that these cells have different diffractive patterns with complementary central intensity distribution in a given plane along the propagation axis. We use the Fresnel approximation to simulate propagation through cells modeled as spheroid-shaped phase objects and to find the cell property that has the dominant influence on this behavior. Starting with images obtained in the reconstruction step of the digital holographic microscopy technique, we developed a code for automated simultaneous individual cell image separation, identification, and counting, even when the cells are partially overlapped on a slide, and accurate measuring of their morphological features. To find the centroids of each cell, we propose a method based on analytical functions applied at threshold intervals. Our procedure separates the mature from the immature red blood cells and from the white blood cells through a decision based on gradient and radius values.

Method of determination of light-scatterer distribution in edge-lit backlight units using an analytical approach.

We present a method to find the optimum distribution of scatterers in an edge-lit lightguide plate (LGP) for rendering a uniform distribution of the outcoupled light. We propose a simple mathematical model describing the light propagation in a waveguide with a distribution of scattering elements located on the lower surface of the waveguide. We have found a differential equation giving the distribution of scattering elements leading to a uniform irradiance along the LGP, and we propose a method to determine the value of the outcoupling coefficient of an individual scattering element from the irradiance (or radiance) measurements. We have verified the validity of this model by performing ray tracing simulations on an LGP with the scattering elements distributed according to the solution of the proposed differential equation, and we have found a quantitative agreement between the analytical results and the simulated ones. Also this model has been used to directly calculate the output power of a given embossed LGP.