A new generation of very efficient high power laser diodes has been developed. The design was optimized for efficient operation of a long cavity device necessary to reduce electrical and thermal resistance. CW operation of a 100µm wide laser at 25C yielded slope efficiency as high as 1.14W/A and 64% electrical-to-optical conversion efficiency. Optical powers as high as 13.5W for thermally limited CW operation and 17.3W for pulsed operation were also recorded.