Passive coherent beam combination of three Nd:YAG lasers using cascaded Michelson-type compound cavities.

A coaxial multibeam passive coherent combination of lasers with improved beam quality is proposed and verified using cascaded Michelson-type cavities, in which 4f optical systems are used to compensate for the beam waist separation between the combined adjacent lasers. A proof-of-concept experiment shows that three 65 W Nd:YAG lasers with an M2 factor of about 5.5 were coherently combined into a 124.4 W single-lobed output improving the M2 factor to 1.36. The central lobe accounted for 76% of the total power, corresponding to a total combined efficiency of 66.7%.