Coherent Beam Combining by Noncollinear Sum-Frequency Generation

Summary form only given. Despite rapid development of fiber laser technologies, highest pulse peak power achievable from fiber lasers eventually approaches limits which are not easy to overcome. Therefore, there is growing interest in methods, which would allow to combine outputs from multiple pulsed fiber lasers into single diffraction-limited beam, and by this enable further scaling. For this reason, numerous coherent and incoherent beam combining methods are being proposed and investigated [1]. Not so well investigated class of beam combining methods is beam combing based on nonlinear interaction. In our earlier work, we have demonstrated beam combining by multiplexing pulses in time, using second-order nonlinear crystal set in noncollinear phase-matching configuration [2]. However, such configuration allows to scale only average power of the beam, leaving pulse energy unchanged (in case of 50 % conversion efficiency). In order to scale pulse energy and peak power, pulses have to be also combined in time, and for this, phase control is needed. Such approach was first proposed by Michailovas et al. [3] and first proof of concept demonstrated by Zhang et al. [4]. However, in previous demonstrations, low-power beams were combined with very low combining efficiency (<; 0.4 % for 4 beams). Here we apply this method to more realistic scenario and demonstrate combining of pulsed beams from 4 high-power fiber amplifiers with efficiency up to 49 %. Moreover, we demonstrate pulse energy and peak power improvement in the combined beam, exceeding peak-power limitations of single fiber amplifier.