Incoherent Space Beam Combining of Fiber-Transmitted Semiconductor Lasers for Oil Well Laser Perforation

This paper demonstrates a 19 x 1 incoherent space beam combiner tailored for oil well laser perforation, which is used for an incoherent laser beam combining of 19 fiber-transmitted semiconductor lasers around a wavelength of 972 nm. The parameters of the combiner and its used optical lens are optimized, which is attributed to the theoretical analysis of the variation law between the radii, the spacing of collimating laser beams, and the spot overlap rate of the combined laser beam, respectively, and the simulation of the cross-sectional energy distribution of the beam combiner. A beam combining the power of 10.159 kW is achieved with an average beam combining efficiency of higher than 98.2%, a beam combining length of 300 mm, and a focal spot diameter of 21 mm. A laser perforation experiment is performed for a granite sample using a 10-kW space incoherent beam laser, and a perforation depth of 960 mm is obtained. This paper underscores the design philosophy of the incoherent space beam combiner with ultra-high laser power, a long beam combining length, a simple structure, and a high downhole transmission safety, and builds the foundation for applications of the incoherent space beam combined laser in the oil well perforation.