Coherent combination of two Tm-doped fiber amplifiers

The efficient coherent combination of two ultrafast Tm-doped fiber amplifiers in the 2-μm wavelength region is demonstrated. The performance of the combined amplifiers is compared to the output characteristics of a single amplifier being limited by the onset of detrimental nonlinear effects. Nearly transform-limited pulses with 830-fs duration, 22-μJ pulse energy, and 25-MW peak power have been achieved with a combining efficiency greater than 90%. Based on this result, it can be expected that 2-μm-ultrafast-fiber-laser systems will enter new performance realms in the near future.