• T. Watanabe, D.F.L. Liu, J.B. Murphy, J. Rose, T.V. Shaftan, T. Tsang, X.J. Wang, L.-H. Yu
  BNL, Upton, Long Island, New York
• P. Sprangle
  NRL, Washington, DC

Funding: Work supported by the Office of Naval Research.

A laser seeded near IR FEL amplifier experiment was initiated at the BNL SDL [1] to explore various schemes of FEL efficiency improvement and generation of short Rayleigh length (SRL) FEL output. The FEL achieved first SASE lasing at 0.8 μm on May 6, 2005. The experimental characterization of the laser seeded FEL output power, spectrum and transverse mode structure evolution will be presented.

[1] A. Doyuran et al., PRSTAB, Vol. 7, 050701 (2004).

• T. Watanabe, D.F.L. Liu, J.B. Murphy, I.P. Pinayev, J. Rose, T.V. Shaftan, J. Skaritka, T. Tanabe, T. Tsang, X.J. Wang, L.-H. Yu
  BNL, Upton, Long Island, New York
• S. Reiche
  UCLA, Los Angeles, California
• P. Sprangle
  NRL, Washington, DC

The design of a Short Rayleigh Length (SRL) FEL amplifier based on the strong focusing VISA undulator [1] is presented in this study. The SRL FEL amplifier will be operating in the IR (0.8 - 1 μm), and consists of a two-meter VISA undulator with a peak seed laser power of about 1 kW. The FEL power and transverse mode evolution along the undulator were investigated using the three-dimensional numerical code GENESIS1.3. The evolution of the FEL output from the undulator exit to the first downstream optics is also studied. The possibility of using the proposed amplifier for a two-stage cascaded HGHG FEL [2] at the BNL SDL is also explored. The design parameters and the numerical results will be presented.

[1] R. Carr et al., PRSTAB, Vol. 4, 122402 (2001). [2] J. Wuard and L.H. Yu, NIMA 475, 104 (2001).