Optical and thermal performance of a toroidal compound parabolic concentrator.

The design, construction, and ray simulation of a new compound parabolic concentrator based on a toroidal shape (toroidal compound parabolic concentrator, TCPC) are addressed. Such analysis indicates that the amount of concentrated radiation is independent of the Sun trajectory. Thus, the TCPC has the advantage of concentrating Sun rays in a spot, and if positioned with an inclination corresponding to the latitude, a solar tracker would not be needed. Experimental measurements with a prototype model are shown to be in good agreement with the simulation results. The possibility of a variety of applications, as natural illumination for this TCPC device, is also pointed out. The simple design, fabrication, and implementation of the TCPC make it an excellent alternative for low concentration in a spot. We present the analysis of the TCPC in natural illumination as one of these applications.

Creation of optical speckle by randomizing a vortex-lattice.

We investigate the number of vortices embedded in a carrier beam needed to produce a speckle pattern and the necessary conditions in terms of their initial distribution and topological charges. A spatial light modulator is used to imprint arrays of vortices in a Gaussian beam, which is propagated in free space for a given distance and then focused in order to induce interaction among the vortices in the focal region. The resulting optical field is analyzed after propagation up to a transverse plane where the carrier beam would recover its initial size in the absence of vortices. The role of different control parameters for obtaining ordered and disordered patterns is discussed. Our experimental study is complemented with a thorough numerical analysis, from which the statistical properties of the disordered patterns are characterized, and the conditions for obtaining well-developed speckle are determined. We also discuss the creation and annihilation of vortex pairs, depending on the initial conditions.

Analytical expressions for Z-scan with arbitrary phase change in thin nonlocal nonlinear media.

Analytical expressions for the normalized transmittance of a thin material with simultaneous nonlocal nonlinear change in refraction and absorption are reported. Gaussian decomposition method was used to obtain the formulas that are adequate for any magnitude of the nonlinear changes. Particular cases of no locality are compared with the local case. Experimental results are reproduced (fitted) with the founded expressions.