• D. Li, K. Imasaki
  ILT, Suita, Osaka
• G.S. Park, Y. Yang
  SNU, Seoul

A renewed interest of Smith-Purcell system has been raised since J. Urata et.al observed a possible exponential gain in their experiment using electron microscope beam. Several theories were presented to calculate the exponential gain. We analyzed this problem in the way of particle in cell simulation, which provides many details in understanding the physics of the radiation from a grating.

• T. Kanai, K. Awazu, S. Yoshihashi-Suzuki
  Osaka University, Suita

Free Electron Laser (FEL) at Osaka University can be continuously varied in the range of 5.0-20.0 μm. A FEL has a double pulse structure. The structure consists of a train of macropulses of the pulse width 15 μs, and each macropulse contains a train of 330 micropulses of the pulse width 5 ps. The tunability and short pulse afford new medical applications such as investigation of protein dynamics and ablation of soft tissues. Precise control of micropulse train is very important for medical applications using FEL because macropulse with long pulse duration sometimes leads to undesirable thermal effects. FEL pulse control system using an acousto optic modulators (AOM) was developed in order to investigate of non-thermal effect between the FEL and tissue. This system provide a very good efficiency (~60 %) and a fast switching speed (>200 ns). A phosphorylated protein was irradiated with FEL that controlled the pulse. These result confirmed that the thermal effect is controlled by pulse duration. This system will be expected as a novel tool for investigation of interaction between the FEL and normal tissue.

• H. Delsim-Hashemi, O. Grimm, J. Rossbach, H. Schlarb, B. Schmidt, P. Schmuser
  DESY, Hamburg
• A.F.G. van der Meer
  FOM Rijnhuizen, Nieuwegein

Funding: DESY

FEL facilities are pushing to achieve higher peak currents mainly by means of compressing bunches longitudinally. This process defines a machine parameter that has to be fine-tuned empirically. Among the operational types of diagnostic tools for longitudinal phase-space are those based on IR spectroscopy. The most commonly used IR spectrometers at the FEL facilities are operating in the scanning mode and are not fast enough to be applicable for monitoring bunch compression. On the other hand, any non-scanning spectrometer may suffer from the low intensity that is available from coherent IR radiation in short time intervals in different wavelengths. The proposed "Single Shot Spectrometer" is based on using gratings as dispersive elements. Pioneering tests with a transmission grating have shown the feasibility of the concept. In a second step, a version with "Reflective Blazed Grating" will be tested and should allow getting the maximum available signal for the whole spectrum and improved resolution. Parallel to the study of optical parts, an array of pyroelectric detectors with integrated multi-channel readout is under development.

• S. Reiche
  UCLA, Los Angeles, California

The Linac Coherent Light Source operates as a Self-Amplified Spontaneous Emission Free-Electron Laser (SASE FEL), where transverse coherence is achieved by the domination of the FEL Eigenmode with the largest growth rate. However complete transverse coherence is not guaranteed because there are multiple eigenmodes with similar growth rates for a low-diffracting FEL, such as the LCLS. In addition the mode purity can be degraded by collective electron beam motion. In this presentation the transverse coherence for the LCLS pulse is investigated with respect to scattering on crystals. The degradation in the contrast and size of the Bragg peaks is analysed for a step wise improved modeling of the experiment (stead-state, time-dependent and start-end simulations). The impact on diffraction experiments, including the proposed experiment to measure the transverse coherence, is discussed.