Effects of mitigation of pixel crosstalk in the encoding of complex fields using the double-phase method

We report on unwanted effects of pixel cross-talk and its mitigation on the experimental realization of the double-phase method with phase-only spatial light modulators. We experimentally demonstrate that a generalized sampling scheme can reduce nonuniform phase modulation due to the pixel cross-talk phenomenon and, consequently, improve the quality of amplitude and phase images obtained with this encoding method. To corroborate our proposal, several experiments to reconstruct amplitude-only as well as fully independent amplitude and phase patterns under different spatial sampling schemes were carried out. We also show how a convenient implementation of the well-known polarization-based phase-shifting technique can be employed to measure the encoded complex field using only a conventional CMOS camera

Encoding of arbitrary micrometric complex illumination patterns with reduced speckle

In nonlinear microscopy, phase-only spatial light modulators (SLMs) allow achieving simultaneous two-photon excitation and fluorescence emission from specific regionof-interests (ROIs). However, as iterative Fourier transform algorithms (IFTAs) can only approximate the illumination of selected ROIs, both image formation and/or signal acquisition can be largely affected by the spatial irregularities of the illumination patterns and the speckle noise. To overcome these limitations, we propose an alternative complex illumination method (CIM) able to generate simultaneous excitation of large-area ROIs with full control over the amplitude and phase of light and reduced speckle. As a proof-of-concept we experimentally demonstrate single-photon and second harmonic generation (SHG) with structured illumination over large-area ROIs

Second-harmonic illumination to enhance multispectral digital lensless holographic microscopy

Multispectral digital lensless holographic microscopy (MDLHM) operating with second-harmonic illumination is shown. Added to the improvement of the spatial resolution of the previously reported MDLHM operating with near-infrared illumination, this second-harmonic MDLHM shows promise as a tool to study the behavior of biological samples under a broad spectral illumination. This illumination is generated by focusing a highly spatially coherent ultrashort pulsed radiation into an uncoated Type 1 β-BaB2O4 (BBO) nonlinear crystal. The second-harmonic MDLHM allows achieving multispectral images of biological samples with enhanced micrometer spatial resolution. The illumination wavelength of the second-harmonic MDLHM can be tuned by displacing a focusing optics with respect to a pinhole; spatially resolved information at different wavelengths of the sample can then be retrieved.Ministerio de Economía y Competitividad (MINECO) (FI2013-40666-P); Generalitat Valenciana (ISIC 2012/03, PROMETEO 2012-021); Universitat Jaume I (P1-1B2012-55); Universidad Nacional de Colombia (UN) (Hermes 28751)

Diffractive control of 3D multifilamentation in fused silica with micrometric resolution

We show that a simple diffractive phase element (DPE) can be used to manipulate at will the positions and energy of multiple filaments generated in fused silica under femtosecond pulsed illumination. The method allows obtaining three-dimensional distributions of controlled filaments whose separations can be in the order of few micrometers. With such small distances we are able to study the mutual coherence among filaments from the resulted interference pattern, without needing a two-arm interferometer. The encoding of the DPE into a phase-only spatial light modulator (SLM) provides an extra degree of freedom to the optical set-up, giving more versatility for implementing different DPEs in real time. Our proposal might be particularly suited for applications at which an accurate manipulation of multiple filaments is required.We acknowledge support from Generalitat Valenciana through the programme PROMETEO-2012-021, University Jaume I through the project P1·1B2013-53, and Ministerio de Economía y Competitividad (MINECO) through the project FIS2013-40666-P. The authors are also very grateful to the SCIC of the Universitat Jaume I for the use of the femtosecond laser

The effects of lasers on bond strength to ceramic materials: A systematic review and meta-analysis

Lasers have recently been introduced as an alternative means of conditioning dental ceramic surfaces in order to enhance their adhesive strength to cements and other materials. The present systematic review and meta-analysis aimed to review and quantitatively analyze the available literature in order to determine which bond protocols and laser types are the most effective. A search was conducted in the Pubmed, Embase and Scopus databases for papers published up to April 2017. PRISMA guidelines for systematic review and meta-analysis were followed. Fifty-two papers were eligible for inclusion in the review. Twenty-five studies were synthesized quantitatively. Lasers were found to increase bond strength of ceramic surfaces to resin cements and composites when compared with control specimens (p-value < 0.01), whereas no significant differences were found in comparison with air-particle abraded surfaces. High variability can be observed in adhesion values between different analyses, pointing to a need to standardize study protocols and to determine the optimal parameters for each laser type

Diffraction-Based Phase Calibration of Spatial Light Modulators With Binary Phase Fresnel Lenses

We propose a simple and robust method to determine the calibration function of phase-only spatial light modulators (SLMs). The proposed method is based on the codification of binary phase Fresnel lenses (BPFLs) onto an SLM. At the principal focal plane of a BPFL, the focal irradiance is collected with a single device just able to measure intensity-dependent signals, e.g., CCD camera, photodiodes, power meter, etc. In accordance with the theoretical model, it is easy to extract the desired calibration function from the numerical processing of the experimental data. The lack of an interferometric optical arrangement, and the use of minimal optical components allow a fast alignment of the setup, which is in fact poorly dependent on environmental fluctuations. In addition, the effects of the zero-order, commonly presented in the diffraction-based methods, are drastically reduced because measurements are carried out only in the vicinity of the focal points, where main light contributions are coming from diffracted light at the BPFL. Furthermore, owing to the simplicity of the method, full calibration can be done, in most practical situations, without moving the SLM from the original place for a given application.This work was supported in part from MINECO under Grant FIS2013–40666-P, Generalitat Valenciana under Grants PROMETEO2012–021 and ISIC 2012/013, and Universitat Jaume I (P1-1B2012-55)

Simulación y control de un sistema de caracterización de pulsos ultracortos

Màster Universitari en Sistemes Intel.ligents (Pla de 2013). Codi: SIU043. Curs acadèmic 2014-2015El objetivo del trabajo presentado es el de diseñar y desarrollar un software capaz de caracterizar temporalmente pulsos de femtosegundo. Adicionalmente, y como trabajo previo, se ha propuesto también el desarrollo de un software capaz de simular este tipo de pulsos. En el caso de la simulación se ha desarrollado un software que genere la traza resultado de aplicar un barrido de dispersión (D-Scan) a partir de los parámetros iniciales y que sea capaz de obtener los parámetros a partir de la traza. Para caracterizar pulsos reales, el software real mide los parámetros accesibles y genera la traza con ellos, para luego calcular el resto

Complex spatial shaping of femtosecond pulses with phase-only spatial light modulators

This thesis is focused on spatial manipulation of laser beams with a single phase only SLM. To achieve it, it is essential to arbitrarily modify a complex field with this kind of devices. In addition, it is intended to introduce new methods to improve existing techniques. In that sense, the experimental implementation of a method known as double-phase is improved and optimized. With that goal in mind, the behavior of SLMs is studied in order to adapt, as far as possible, the experimental response of these devices. Finally, the optimized method is used in several applications to obtain real results comparable to other well-known optical methods.La posibilidad de definir, de forma arbitraria, parámetros como el patrón de irradiancia o la fase de un haz láser ha contribuido a adecuar las fuentes de luz a los requisitos concretos de cada usuario para sus distintas aplicaciones. Como resultado, el desarrollo de nuevas técnicas que permitan realizar este tipo de control se ha convertido en un tema esencial que beneficia a gran cantidad de aplicaciones. Los moduladores espaciales de luz (SLMs por sus siglas en inglés) son dispositivos que permiten control directo de estas propiedades. Generalmente, los SLMs son capaces de modular en tiempo real y de forma programable uno de estos parámetros (amplitud o fase). No obstante, para controlar los dos parámetros al mismo tiempo es necesario el empleo de varios dispositivos o el desarrollo de alguna técnica que permita realizar este control con un solo dispositivo.Programa de Doctorat en Cièncie