Observation of self-amplified spontaneous emission in the near-infrared and visible wavelengths

We report evidence of self-amplified spontaneous emission (SASE) at 1064 and 633 nm. To our knowledge, these are the first measurements of SASE at such a short wavelength and employ the smallest period wiggler, 8.8 mm, used to date in a successful SASE experiment. The experiments were performed with the MIT microwiggler at the Accelerator Test Facility at BNL. Single-pass, on-axis microwiggler emissions within a 25 nm bandwidth have been recorded as a function of beam charge and show a clear enhancement over spontaneous emission. For the measurement at 1064 nm, a single micropulse at 34 MeV with a variable charge of 0 endash 1 nC and less than 5 ps full width at half maximum bunch length was passed through the microwiggler and emissions into a limited solid angle and bandwidth, selected by an aperture and interference filter, were focused onto a silicon photodiode. Enhancement of the emissions, from 2 to 6 times the spontaneous emission level, was observed at the highest charges. In addition, we observed SASE gain at a wavelength of 633 nm at a beam energy of 48 MeV, without detailed measurements. copyright 1998 The American Physical Society