With high-temporal coherence and low-phase noise, narrowlinewidth lasers have important applications in spectroscopy, holography, and coherent detection. At present, ultra-narrowlinewidth lasing is generated by solid-state, optical fiber, and semiconductor lasers, which serve as a good light source for scientific research and industrial applications. In this article, we summarize the fundamental techniques and review recent developments in narrow-linewidth lasers. Moreover, typical applications of narrow-linewidth lasers are discussed to provide reliable and easy-to-use references for comparing the performance of narrow-linewidth lasers.
Uniform illuminance over the expanded exit pupil is an important requirement for waveguide display systems with a wide field of view (FOV). To address this issue, we develop a monochromatic binocular waveguide display in this paper. Two surface-relief diffraction gratings are designed as in-couplers and out-couplers. The parameters of the gratings are optimized to achieve uniform diffraction efficiency distributions over a broad angular range. The grating couplers enable the system to realize a diagonal FOV of 40°. A freeform surface prism is designed as the projection optics. The diameters of the two exit pupils are 12 mm in the expanding direction at an eye relief of 19 mm.
Point clouds registration is an important step for laser scanner data processing, and there have been numerous methods. However, the existing methods often suffer from low accuracy and low speed when registering large point clouds. To meet this challenge, an improved iterative closest point (ICP) algorithm combining random sample consensus (RANSAC) algorithm, intrinsic shape signatures (ISS), and 3D shape context (3DSC) is proposed. The proposed method firstly uses voxel grid filter for down-sampling. Next, the feature points are extracted by the ISS algorithm and described by the 3DSC. Afterwards, the ISS-3DSC features are used for rough registration with the RANSAC algorithm. Finally, the ICP algorithm is used for accurate registration. The experimental results show that the proposed algorithm has faster registration speed than the compared algorithms, while maintaining high registration accuracy.
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