We have demonstrated direct and stable flat-top beam emission from a passively Q-switched microchip laser, featuring an intracavity spot-defect for mode selecting. By adjusting the distance between the focusing lens and the microchip laser, the Gaussian, flat-top, and doughnut-shaped mode can be achieved separately. The flat-top mode is obtained due to the equally weighted superposition of Gaussian and doughnut-shaped mode. By using the self-injection seeding technique, the timing jitter of these three kinds of mode can be reduced effectively.

Absolute phase retrieval has been widely studied, as it is not much influenced by the discontinuity and occlusion of objects in phase-measuring profilometry. In the practical measurement, however, fringe order determination is by no means easy when the grayscale of deformed patterns is degraded because of uneven reflectivity or the large curvature of measured objects. We introduce a phase-shifting coding (PSC) method to overcome that problem. In the PSC method, fringe order is encoded by the phase-shifting amounts of additional fringe patterns, and the decoding algorithm to retrieve absolute phase is designed on the basis of phase difference and neighborhood consistency. The special statistical filtering and self-correcting filtering methods are utilized to eliminate absolute phase errors. Experiment results demonstrate that the proposed PSC method is effective and has strong robustness in grayscale degradation regions.