A nanometer beam size monitor for ATF2

We developed an electron beam size monitor for nanometer scaled beam sizes. It uses a laser interference fringe for a scattering target with the electron beam. The target beam size for the monitor is 25–6000 nm to achieve and confirm the 37 nm design beam size of ATF2, a final focus test facility for the ILC. Resolution of less than 10% for the full range is shown to be realistic, with a precise fringe control system. We describe the overall design, implementation, and performance of the monitor.