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In this paper, we develop a new image denoising method based on block-matching and transform-domain filtering. The developed method is derived from the current state-of-the-art denoising method (BM3D). We separate the 3D transform in the original method to two steps 1D transform, to further enhance the sparsity for signals whose elements are highly similar and to weaken the sparsity for those signals whose elements are dissimilar. Because the 1D filtering is on highly similar elements and the 2D filtering on image blocks are all removed, the image details can be better reserved and fewer artifacts are introduced than original method. Experimental results demonstrate that the developed method is competitive and better than some of the current state-of-the-art denoising methods in terms of peak signal-to-noise ratio, structural similarity, and subjective visual quality.

The crucial problem of DKDP crystal for third harmonic generation (THG) is its low laser-induced damage threshold with respect to KDP, which greatly limits energy fluence of the output laser and crystals' useful life. In order to study the relation between wavelength and laser-induced damage of DKDP, we carried out some related experiments in present work. DKDP crystal was conventionally grown from 80%-deuterated solution of high pure materials and the crystal was cut to tripler sample of type II. Laser-induced damage threshold of DKDP crystal for THG was measured under different wavelengths and the effect of laser annealing was also investigated. The experiment shows that laser annealing could obviously improve laser-induced damage threshold of DKDP crystal. The threshold is improved to 1.4, 1.9 or 2.7 times that before annealing for fundamental, second or third harmonic, respectively. Thus laser annealing is an effective approach to enhance laser-induced damage resistance of DKDP crystal.

This paper shows DKDP crystals of different deuterium content are cut for type I non-critical phase-matching with the direction at 90° to the crystal Z axis (=90°) and at 45° to the crystal X axis (=45o), and are measured at the FHG experiments with fundamental frequency wavelength 1064nm and 1053nm, respectively. The optimum deuterium content of DKDP crystal, that can achieve non-critical phase-matching at FHG experiments, is confirmed by measuring the relationship of deuterium content and phase-matching angle.