First observation of optical current noise suppression below the shot-noise limit

In this paper we present experimental results that demonstrate noise suppression in the optical regime, for a rela-tivistic e-beam, below the well-known classical shot-noise limit. Shot-noise amplitude is linear to the e-beam current due to the random nature of particles emission (Pois-son statistics) from the cathode. Plasma oscillations driven by collective Coulomb interaction during beam drift between the electrons of a cold intense beam are the source of this phenomenon [1]. The effect was experimentally demonstrated by measuring Optical Transition Radiation (OTR) power per unit e-beam pulse charge. The noise suppression effect implies beam charge homogenization (sub-Poissonian particle number distribution) and therefore the spontaneous radiation emission from such a beam would also be suppressed (Dicke's subradiance [2]). This can be utilized to suppress SASE radiation emission in FEL [3],[4]) and enhance the coherence [5] of seed-injected FELs [6] beyond the classical coherence limits.