The requirements on laser power sources for advanced accelerator concepts are formidable. These requirements are driven by the need to deliver 5 TeV particles at luminosities of 1033 -- 1034 cm-2 sec-1. Given that optical power can be transferred efficiently to the particles these accelerator parameters translate into single pulse laser output energies of several kilojoules and rep rates of 1-10 kHz. The average laser output power is then 10-20 MW. Larger average powers will be needed if efficient transfer proves not to be possible. A laser plant of this magnitude underscores the importance of high wall plug efficiency and reasonable cost in $/Watt. The interface between the laser output pulse format and the accelerator structure is another area that drives the laser requirements. Laser accelerators break up into two general architectures depending on the strength of the laser coupling (ratio of particle accelerating field to the laser optical electric field). For strong coupling mechanism (beat wave and grating linac), the architecture requires many "small" lasers powering the accelerator in a staged arrangement. For the weak coupling mechanisms (inverse free electron laser and inverse Cherenkov), the architecture must feature a single large laser system whose power must be transported along the entire accelerator length. Both of these arrangements have demanding optical constraints in terms of phase matching sequential stages, beam combining arrays of laser outputs and optimizing coupling of laser power in a single accelerating stage.