Papers by Keyword: Self-Focusing

Abstract: In this paper, we theoretically and experimentally investigated the controllable nonlinear focusing of the weak laser based on the induced nonlinear effects. We obtained an exact analytical solution to the weak laser beam when the high power laser beam is unchangeable during propagation. We also discussed the different pump parameters how to influence the focusing and experimentally partly verify the theoretical analysis. The results show that the focusing of weaker beam was jointly controlled by the power, width and wavelength of pump laser.

Abstract: Guided waves (GW) based methods are a promising tool for structural health monitoring (SHM) of plate-like metallic and composite structures in which high safety standards are required. In this paper we present research with the aim to design and manufacture a prototype of Lamb waves (LW) SHM system. Two approaches can be applied for SHM of plate-like structures. One of them can be based on a sparse array and damage imaging involving incoherent summation of signals envelope. The second approach involves phased arrays with transducers spaced at a distance lower than half wavelength of the excited Lamb-mode. The influence of an arrays parameters on beamforming of Lamb waves is discussed in the case of linear array. It appears that an unequivocal localization of damage on a plate requires a 2D arrays topology; therefore a star-shaped active array was designed and manufactured for the developed SHM system. Two signal processing approaches were applied for that array, the standard one, based on the delay and sum (DAS) synthetic aperture focusing scheme, and the second one, using a self-focusing technique to obtain the separate images for each scatterer existing in the plate.

Abstract: We implement the concept of the distributed electrode, which allows to improve the modal behavior of lasers and to reduce spatial-hole burning effects by preferentially localizing current injection in the center of the structure, hence discriminating the optical mode. We report the first realization of distributed electrode lasers emitting at 808 nm with the measured full width at half maximum (FWHM) angle of the minimal horizontal angle as 3.8° while the maximum continuous-wave output power is up to 4 W and high slope efficiencies as high as 0.95 W/A.