Why are lasers inefficient? Is it because of the heat lost during lasing? Why couldn't there be thermocouples or turbines in parts of the cooling circuits to extract something out of that heat?
Not all lasers are inefficient. Infrared diodes are quite efficient. This paper shows 64% electrical to optical conversion efficiency: http://www.jdsu.com/ProductLiterature/paper_hipower_910_980_laser_diodes.pdf
An argon gas laser on the other hand is quite inefficient.