  Laser brightness is a measure of the ability to de- liver intense light to a
target, and encapsulates both the energy content and the beam quality. High
brightness lasers requires that both parameters be maximised, yet standard
laser cavities do not allow this. For example, in solid-state lasers multimode
beams have a high energy content but low beam quality, while Gaussian modes
have a small mode volume and hence low energy extraction, but in a good quality
mode. Here we over- come this fundamental limitation and demonstrate an optimal
approach to realising high brightness lasers. We employ intra- cavity beam
shaping to produce a Gaussian mode that carries all the energy of the multimode
beam, thus energy extraction and beam quality are simultaneously maximised.
This work will have a significant influence on the design of future high
brightness laser cavities.
