Laser diode array with diffraction limited divergence

The development of laser weapons has a profound impact on military missions throughout the services. An ideal laser system must be capable of delivering hundreds of kilowatts of average power to a target at multi-kilometer ranges through adverse atmospheric conditions. The highest power within diffraction limited divergence was demonstrated with solid state and fiber lasers. However, development of multi-gain media systems where gain media (crystal or fiber) pumped by laser diodes reduces the overall efficiency of the laser system and therefore increases the total power requirements. On the other hand, high power laser diode (LD) arrays that demonstrate highest efficiency and compactness suffer from high divergence resulted from inevitable multimode regime. The new approach we propose levels of LD control and integration. It includes a new design of a semiconductor waveguide and an external cavity geometry with volume Bragg gratings (VBGs) providing spectral narrowing and angular divergence down to diffraction limit for high pumping currents; coherent combining by means of multiplexed VBGs that enable efficient radiation exchange between individual LDs and phase locking to provide a coherent LD array; spectral combining of coherent LD arrays by a sequence of multiplexed VBGs.