Beam profile monitors for very small transverse and longitudinal dimensions using laser interferometer and heterodyne techniques

In future e(+)e(-) linear colliders of 0.5-1 TeV center-of-mass energy region, very small beam sizes will be used at the interaction region in order to get enough beam-beam luminosity. Typical design parameters assume a cross section of 3-5 nm by 300 nm in vertical and horizontal, respectively, and a bunch length of 0.1 mm. In order to measure the nanometer vertical size, we use laser interference fringes. By scanning the electron beam over the fringe pattern and monitoring the high-energy gamma rays due to Compton scattering, beam information can be obtained. The modulation depth in the gamma-ray flux gives the spot size information. This method was used in the Final Focus Test Beam (FFTB) test at SLAC, and a 70-nm spot was measured. To measure the longitudinal bunch length, a new method, utilizing a laser-heterodyne technique, will be proposed in this paper.