Generation of periodic and quasi-periodic two-dimensional non-diffractive beams with inhomogeneous polarization.

In this work, two-dimensional periodic and quasi-periodic non-diffractive spatial inhomogeneous polarization optical fields are generated, numerically and experimentally, by the superposition of multiple plane waves with different polarizations. For the experimental implementation of the fields, synthetic phase holograms are employed in conjunction with half-wave and quarter-wave retarder films as polarization modulators. The obtained spatially inhomogeneous polarization optical fields show good quality and are in good agreement with numerical results. The proposed method is highly efficient for the generation of these types of optical fields.

Simple techniques to generate binary periodical polarization fields.

We report two new, to the best of our knowledge, methods to generate polarization gratings, whose basic cells are formed by sections that are orthogonally polarized. One of the methods employs a spatial filtering setup that modulates the diffraction orders in the Fourier domain of a Ronchi grating, with two orthogonal polarizations. In the second method, a binary phase modulation, generated by a liquid crystal device, is converted into orthogonal polarizations in different zones of an incident beam. The analysis of the generated polarization states is made at 1/4 of the Talbot distance of the generated gratings. The experimental results are in good agreement with the theoretical description.

Optical manipulation using optimal annular vortices.

We discuss a simple method to generate a configurable annular vortex beam (AVB) with the maximum possible peak intensity, employing a phase hologram whose transmittance is the phase of a Bessel beam. Due to its maximum intensity, the AVB provides the optimal density of the orbital angular moment. Another attribute of the generated AVB is the relatively high invariance of the intensity profile when the topological charge is changed. We demonstrate the advantages and flexibility of these AVBs for optical trapping applications.

Optimum generation of annular vortices using phase diffractive optical elements.

An annular vortex of arbitrary integer topological charge q can be obtained at the Fourier domain of appropriate phase diffractive optical elements. In this context we prove that the diffractive element that generates the vortex with maximum peak intensity has the phase modulation of a propagation-invariant qth order Bessel beam. We discuss additional advantages of this phase element as annular vortex generator.

Liquid crystal microlens arrays recorded by polarization holography.

We report the characterization of diffractive microlens arrays (MAs) using a polarization holographic approach assisted by a spatial light modulator (SLM), in a nematic liquid crystal (NLC) cell. The MAs were recorded in the photoaligning substrates of the cell and then replicated in the NLC bulk, through the surface interactions. The transparency of the NLC on a wide range of wavelengths and the ability to tune its optical birefringence, through an external voltage, allowed us to create MAs with high efficiency. We have presented the results obtained for diverse MAs configurations, composed by spherical and cylindrical microlenses and characterized by different focal lengths. The efficiency reaches a value of 90%, at a wavelength of 633 nm.

Comparing efficiency and accuracy of the kinoform and the helical axicon as Bessel-Gauss beam generators.

We compare two phase optical elements that are employed to generate approximate Bessel-Gauss beams of arbitrary order. These elements are the helical axicon (HA) and the kinoform of the desired Bessel-Gauss beam. The HA generates a Bessel beam (BB) by free propagation, and the kinoform is employed in a Fourier spatial filtering optical setup. As the main result, it is obtained that the error in the BBs generated with the kinoform is smaller than the error in the beams obtained with the HA. On the other hand, it is obtained that the efficiencies of the methods are approximately 1.0 (HA) and 0.7 (kinoform).

Pure two-dimensional polarization patterns for holographic recording.

Two-dimensional (2D) polarization patterns are achieved by the interference of two pairs of beams with perpendicular planes of incidence and orthogonal polarizations (i.e. linear or circular). In both cases, imposing a phase shift of π/2 between consecutive beams contains the amplitude modulation of the optical field in the superposition region and, thus, pure 2D polarization patterns are created. The recording of these interference fields in a polarization-sensitive material, namely an amorphous azopolymer, creates reconfigurable 2D periodic microstructures with peculiar diffraction properties.

Single-step polarization holographic method for programmable microlens arrays.

Optical microsystems have become important tools for imaging, optofluidics, and sensor applications. Here we show a versatile method to create microlens arrays (MAs) exploiting spatial-light-modulator-assisted polarization holography, which enables an efficiency of diffraction up to 100%. We demonstrate the large flexibility of the proposed approach by codifying mixed MAs, i.e., composed of spherical and cylindrical lenses with different focal lengths, either positive or negative. Reconfigurable MAs with 70% total diffraction efficiency have been recorded on a photosensitive polymer that exhibits linear photoinduced birefringence with long time stability as well as optical and thermal reversibility. The good quality of the MA has been shown by a digital holographic test.

Efficient generation of periodic and quasi-periodic non-diffractive optical fields with phase holograms.

The superposition of multiple plane waves with appropriate propagation vectors generates a periodic or quasi-periodic non-diffractive optical field. We show that the Fourier spectrum of the phase modulation of this field is formed by two disjoint parts, one of which is proportional to the Fourier spectrum of the field itself. Based on this result we prove that the non-diffractive field can be generated, with remarkable high accuracy and efficiency, in a Fourier domain spatial filtering setup, using a synthetic phase hologram whose transmittance is the phase modulation of the field. In a couple of cases this result is presented analytically, and in other cases the proof is computational and experimental.

Generation of Airy solitary-like wave beams by acceleration control in inhomogeneous media.

We investigate the propagation of Airy beams in linear gradient index inhomogeneous media. We demonstrate that by controlling the gradient strength of the medium it is possible to reduce to zero their acceleration. We show that the resulting Airy wave beam propagates in straight line due to the balance between two opposite effects, one due to the inhomogeneous medium and the other to the diffraction of the beam, in a similar way as a solitary wave in a nonlinear inhomogeneous medium. Going even further we were able to invert the sign of the acceleration of the beam.

Periodic and quasi-periodic non-diffracting wave fields generated by superposition of multiple Bessel beams.

We discuss a computer generated hologram whose transmittance is defined in terms of the Jacobi-Anger identity. If the hologram is implemented with a continuous phase spatial light modulator it generates integer-order non-diffracting Bessel beams, with a common asymptotic radial frequency, at separated propagation axes. On the other hand, when the hologram is implemented with a low-resolution pixelated phase modulator, it is possible to generate multiple Bessel beams with a common propagation axis. We employ this superposition of multiple Bessel beams to generate non-diffracting periodic and quasi-periodic wave fields.

Quality management in health care: a 20-year journey.

In this article, the total quality programme in the Spanish healthcare system (1986-1992) and the subsequent quality improvement steps that have led to definition and implementation of such an integrated framework, seeking a quality management system and patient safety, are discussed.

Efficient generation of an arbitrary nondiffracting Bessel beam employing its phase modulation.

We report a highly efficient method for generation of any high-order nondiffracting Bessel beam employing a phase hologram whose transmittance coincides with the phase modulation of such a beam. It is remarkable that the Bessel beam generated by this hologram, at the plane of this device, has peak amplitude higher than the amplitude of the beam employed to illuminate it.

Pixelated phase computer holograms for the accurate encoding of scalar complex fields.

We discuss a class of phase computer-generated holograms for the encoding of arbitrary scalar complex fields. We describe two holograms of this class that allow high quality reconstruction of the encoded field, even if they are implemented with a low-resolution pixelated phase modulator. In addition, we show that one of these holograms can be appropriately implemented with a phase modulator limited by a reduced phase depth.