• X.J. Wang, Y. Hidaka, J.B. Murphy, B. Podobedov, H.J. Qian, S. Seletskiy, Y. Shen, X. Yang
  BNL, Upton, Long Island, New York
• B. Hafizi
  Icarus Research, Inc., Bethesda, Maryland
• J. Penano, P. Sprangle
  NRL, Washington, DC

The NSLS Source Development Laboratory (SDL) has been a world leader in the development of laser seeded free electron lasers (FEL). Recently we initiated an experimental program to investigate a Self-Amplified Spontaneous Emission (SASE) FEL in both the exponential gain and the saturation regimes. We have experimentally demonstrated the saturation of a SASE FEL in the visible to near IR. The experimental characterization of the transverse and spectral properties of the SASE FEL along the undulator for a uniformed and tapered undulator will be presented. In addition, an efficiency enhancement concept for a SASE FEL, which involves a step wiggler taper in the exponential gain regime prior to trapping, will be presented. Simulations of the SASE FEL processes will employ the GENESIS FEL code.