Laser-based profile monitor for electron beams

High performance TeV energy electron/positron colliders (LC) are the first machines to require online, non-invasive beam size monitors for micron and submicron for beam phase space optimization. Typical beam densities in the LC are well beyond the threshold density for single pulse melting and vaporization of any material, making conventional wire scanners ineffective. Using a finely focused, diffraction limited high power laser, it is possible to devise a sampling profile monitor that, in operation, resembles a wire scanner. Very high resolution laser-based profile monitors have been developed and tested, first at FFTB (SLAG) and later at SLC and ATF. The monitor has broad applicability and we review here the technology, application and status of ongoing research programs.