The phased fiber laser array is an important technique for achieving high power and high beam quality laser output. The adaptive fiber-optics collimator (AFOC) is a key element of the phased fiber laser array, which is used to transfer the laser from fiber to free space and precisely control the direction of the outgoing collimating beam. To achieve kilowatt-level and higher power laser output from AFOC, it is necessary to design the collimating lens group to meet the high-power demand and analyze the optical-mechanical-thermal coupling effect of this device. According to the dynamic range of AFOC, a large aperture collimating lens group adapted to large deflection angle is presented in this paper. By using the finite element analysis method, the laser is simplified as the body heat source, and the temperature field and stress field at each lens of the AFOC at 1kW-10kW are simulated, and distribution is Gaussian. The wavefront phase analysis of the outgoing beam shows that the aberrations caused by heat absorption of the optical mirror group are mainly spherical aberrations and defocusing terms. At a laser power level of 6kW, the beam quality factor β of the collimated beam can be reduced from 4.6 to 1.6 by compensating thermal defocusing. This study provides a theoretical basis for the design and optimization of high-power AFOC and offers theoretical support for evaluating their reliability.
High-power and high-quality pulsed fiber lasers with low repetition frequency are widely applied to various fields ranging from basic science to industrial applications. Coherent beam combining (CBC) is a significant method to obtain that beam, but few methods used for large-scale CBC of pulsed fiber lasers with low repetition frequency were presented. To realize it, a new method based on a continuous carrier was designed, where the continuous wave worked as the beacon signal, and the stochastic parallel gradient descent algorithm was employed for phase locking and tilt correction. The beam combining experiment revealed that the combining efficiency of two lasers with a repetition frequency of 15 kHz and a pulse width of 100 ns was 95%, and the fringe contrast in the center of the far-field spot was improved about three times. This method promises to be furtherly applied to combine the pulsed lasers with lower repetition frequency and narrower pulse width. These results pave the way for large-scale CBC of high-power and high-quality pulsed fiber lasers.
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