Yu, L.H.
(Li-Hua Yu)

MOAIS03 R&D Experiments at BNL to Address the Associated Issues in the Cascading HGHG Scheme
Li-Hua Yu (BNL, Upton, Long Island, New York)

We discuss several experiments that can be carried out at BNL's DUVFEL to address several issues associated with cascaded HGHG FELs. These include: Chirped Pulse Amplification (CPA); HGHG with seed shorter than electron bunch length; 8th harmonic HGHG (from 800nm to 100nm); Regenerative synchronization of seed pulse and electron bunch; Tuning of HGHG without changing seed, proposed by Timur Shaftan; Cascading using NISUS and VISA: from 400nm to 100nm to 50nm. These experiments may have important impact on the development of multi-stage cascaded HGHG FELs.

WEAIS01 Experimental Demostration of Wavelength Tuning in High-Gain Harmonic Generation Free Electron Laser
Timur Shaftan, Erik Johnson, Sam Krinsky, Henrik Loos, James Murphy, George Rakowsky, James Rose, Brian Sheehy, John Skaritka, Xijie Wang, Zilu Wu, Li-Hua Yu (BNL/NSLS, Upton, Long Island, New York)

We present experimental results on tuning of the HGHG FEL output wavelength while holding the input seed wavelength constant. Using compression of the initially chirped beam in the HGHG dispersion section we have measured the wavelength shift of about 1% around the nominal value of 266 nm. The tuning range is expected to reach 3 % after the dispersive section upgrade at the DUV FEL. An optimized design based on this principle, using additional linac sections, would have the capability of providing full tunability.

WEAOS02 Spectral Phase Modulation and chirped pulse amplification in High Gain Harmonic Generation
Zilu Wu, Erik Johnson, Sam Krinsky, Henrik Loos, James Murphy, Timur Shaftan, Brian Sheehy, Yuzhen Shen, Xijie Wang, Li-Hua Yu (BNL/NSLS, Upton, Long Island, New York)

High Gain Harmonic Generation (HGHG), because it produces longitudinally coherent pulses derived from a coherent seed, presents remarkable possibilities for manipulating FEL pulses. If spectral phase modulation imposed on the seed modulates the spectral phase of the HGHG in a deterministic fashion, then chirped pulse amplification, pulse shaping, and coherent control experiments at short wavelengths become possible. In addition, the details of the “transfer function” will likely depend on electron beam and radiator dynamics and so prove to be a useful tool for studying these. Using the DUVFEL at the National Synchrotron Light Source at Brookhaven National Laboratory, we present spectral phase analyses of both coherent HGHG and incoherent SASE ultraviolet FEL radiation, applying Spectral Interferometry for Direct Electric Field Reconstruction (SPIDER), and assess the potential for employing compression and shaping techniques.

MOPOS67 The Upgrade of the DUV-FEL Facility at the BNL
Xijie Wang, Henrik Loos, James Murphy, George Rakowsky, James Rose, Brian Sheehy, Yuzhen Shen, John Skaritka, Zilu Wu, Li-Hua Yu (BNL/NSLS, Upton, Long Island, New York)

The DUV-FEL at BNL, is the world’s only facility dedicated to laser-seeded FEL R&D and its applications. The HGHG at the DUV-FEL reached saturation at 266 nm with 800 nm seeding [1] in 2002. Since then, the first chemical science experiment – ion pair imaging, was successfully completed [2].The DUV-FEL linac is being upgraded from 200 to 300 MeV to enable the HGHG FEL to produce 100 μJ pulses of 100 nm light. This will establish the DUV FEL as a premier user facility for XUV radiation. The upgraded facility will also enable several critical R&Ds for a future X-ray FEL based on HGHG, such as cascaded HGHG and higher harmonic HGHG (n>5). The upgraded HGHG will operate at the 4th harmonic with the seed laser at 400nm. The increase of the electron beam energy will be accomplished by installing a 5th linac cavity and two 45 MW klystrons. New modulator and dispersion sections vacuum chambers will be manufactured to accommodate new matching optics and 8th harmonic HGHG. The status of the DUV-FEL upgrade and other FEL R&D opportunities will be discussed.

THPOS62 Preliminary Measurements of the High-Gain FEL Radiation Properties along the Radiator
Timur Shaftan, Henrik Loos, Brian Sheehy, Li-Hua Yu (BNL/NSLS, Upton, Long Island, New York)

We present experimental results on evolution of properties of the DUV FEL output radiation along the radiator. Intercepting the electron beam at the different locations inside the undulator we recorded and analyzed transverse profiles, spectra and intensity of the FEL output. Shot-to-shot fluctuations of the FEL radiation may significantly affect the accuracy of measurement. In the paper we present and discuss a single-shot measurement technique, based on a special imaging system.