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An efficient two-scan connected component labelling (CCL) algorithm is proposed for a general purpose graphics processing unit (GPGPU). Compared to other GPU CCL algorithm, this algorithm has three distinct features. First, block-based and run-based strategies are combined in the first scan to simplify the equivalence label resolving process. Secondly, a novel labelling method for the GPU is introduced by constructing a forest of rooted trees using only 16-bit value for each node. Thirdly, the whole algorithm can be implemented in the GPU shared memory and minimise global memory bandwidth consumption. Experiments show that the algorithm achieves a speedup of between two and five times compared to other state-of-the-art GPU and CPU CCL algorithms.

A method for selective excitation of InceGaussian modes is presented. The method is based on the spatial distributions of Ince-Gaussian modes as well as the transverse mode selection theory. Significant diffraction loss is introduced in a resonator by using opaque lines at zerointensity positions, and this loss allows to excite a specific mode; we call this method ''loss control.'' We study the method by means of numerical simulation of a half-symmetric laser resonator. The simulated field is represented by angular spectrum of the plane waves representation, and its changes are calculated by the two-dimensional fast Fourier transform algorithm when it passes through the optical elements and propagates back and forth in the resonator. The output lasing modes of our method have an overlap of over 90 % with the target Ince-Gaussian modes. The method will be beneficial to the further study of properties and potential applications of Ince-Gaussian modes.

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