Laser beam alignment is very important for high-power laser facility. Long laser path and large-aperture lens for alignment are generally used, while the proposed alignment system with a wedge by far-field sampling technique reduces both space and cost requirements. General alignment system for large-aperture laser beam is long in distance and large in volum because of taking near-field sampling technique. With the development of laser fusion facilities, the space for alignment system is limited. A new alignment system for large-aperture laser beam is designed to save space and reduce operating costs. The new alignment for large-aperture laser beam with a wedge is based on far-field sampling technique. The wedge is placed behind the spatial filter to reflect some laser beam as signal light for alignment. Therefore, laser beam diameter in alignment system is small, which can save space for the laser facility. Comparing to general alignment system for large-aperture laser beam, large-aperture lenses for near-field and far-field sampling, long distance laser path are unnecessary for proposed alignment system, which saves cost and space greatly. This alignment system for large-aperture laser beam has been demonstrated well on the Muliti-PW Facility which uses the 7th beam of the SG-Ⅱ Facility as pump source. The experimental results indicate that the average near-field alignment error is less than 1% of reference, and the average far-filed alignment error is less than 5% of spatial filter pinhole diameter, which meet the alignment system requirements for laser beam of Multi-PW Facility.
We investigate the random phase fluctuations of coherent laser propagate through the turbulent atmosphere, and introduce a model of its impact on optical heterodyne reception free space coherent laser optical communication (FSO) system. A polarization based shearing interferometer is used to detect the distorted laser wave-front and reconstruct the wave-front after propagate through a 1Km near-ground atmospheric channel. Further, the heterodyne efficiency of the heterodyne reception system would be given under special consideration of the mismatch between the signal field and the local oscillator. By analyzing the heterodyne efficiency data and the real-time atmospheric coherence length data, a mathematical model of the effects of atmospheric turbulence on FSO system performance is given.