Coherent beam combining (CBC) is one of the methods for power scaling of high power lasers . In the scientific literatures a low power narrow linewidth source is used for CBC, however in this report, a low cost diode laser source (spectral bandwidth <10 MHz) is used to fabricate near diffraction-limited 300 W fiber laser with CBC method. The diode laser is amplified by a preamp fiber amplifier and then divided in to three channels. Each channel is amplified to achieve 120W output with homemade power amplifiers. A 1×3 diffractive optical element is used to combine the output of the amplifiers with ~83% efficiency. Fig. 1 shows the schematic of our experimental setup. Active phase locking is achieved with the stochastic parallel gradient descent (SPGD) method.
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