YAG bonded:One can be used to improve the thermal lens effect in during the laser excitation, on the other hand can reduce the size of the laser, the laser miniaturization,integration.
Diffusion Bonded Crystals are crystals consisting of two, three or more parts with different doping levels or different dopant, usually one laser crystal and one or two undoped crystals combined by optical contact and further bonded under high temperature. The Bonded laser chips are generally manufactured from Nd:YAG and Cr:YAG diffusion bonded together and laser 1064nm while pumped at 808nm either by trabsversal pumping or longitudinal pumping setups. Experiments show that the bonded crystals can effectively reduce the temperature of the laser crystal, reducing distortion caused by the end of the thermal lens effect.
Advantages of YAG Bonded Crystals 
 High damage threshold Improve beam quality Decrease thermal effect Improve efficiency Compact size,etc.
Standard Diffusion Bonded Crystals
Cr4+:YAG +Nd:YAG
YAG + Nd:YAG + YAG
YAG+Nd:YAG+Cr4+:YAG+YAG
YAG+Nd,CE:YAG+Cr4+:YAG+YAG