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Diamond‐based concept for combining beams at very high average powers

Ever since the laser's invention, there has been great interest in increasing beam output power without detriment to its coherence. Despite great advances having been obtained through the use of a diverse range of approaches, steady‐state beam powers above ten kilowatts remain a significant challenge for solid‐state lasers due to the heightened impact of detrimental nonlinear effects such as thermal lensing. Multiplexing several lasers using beam combination represents a method for surpassing the power barriers of single lasers. Here we propose and demonstrate a novel approach to beam combination and power scaling based on Raman conversion in diamond. Power from multiple non‐collinear pump beams is efficiently transferred onto a single Stokes beam in a single‐pass amplifier. Using three mutually‐independent nanosecond pulsed beams from a free‐running‐linewidth 1064 nm laser, 69% of the total peak pump power of 6.7 kW was transferred onto a TEM00 Stokes seed pulse at 1240 nm in a 9.5 mm long diamond crystal. Compared to other beam combination techniques, diamond beam combination has advantages of relaxed constraints on pump beam mutual coherence, while enabling narrowband output. Thermal considerations for extending from low duty‐cycle to continuous wave operation and higher power levels are discussed.