We propose a technique for measuring the length of an electron bunch from a linear accelerator without interrupting the electron beam. Bunch lengths are measured by observing off-axis undulator radiation. The wavelength of undulator radiation increases with the angle of emission. At angles as large as 10 degrees, the wavelength may be longer than the electron bunch, and as a result coherence ef...

3 Paul Scherrer Institute, Villigen PSI, 5232, Switzerland Abstract Energy extraction efficiency of a free electron laser (FEL) can be increased when the undulator is tapered after the FEL saturation. By use of ray equation approximation to combine the one-dimensional FEL theory and optical guiding approach, an explicit physical model is built to provide insight to the mechanism of the electron...

The productions of positrons in sufficient quantities is one of the necessities for either the TESLA or the S-Band Linear Collider project. One of the promising possibilities is to guide the high energy electron beam through a superconducting helical undulator producing synchrotron radiation which would in turn be directed onto a target for positron production [1]. A helical undulator has two a...

We analyze properties of electromagnetic radiation in helical undulators with a particular emphasis on the orbital angular momentum of the radiated photons. We demonstrate that all harmonics higher than the first one radiated in a helical undulator carry an orbital angular momentum. We discuss some possible applications of this phenomenon and the ways of effective generation of these photons in...

We describe a proposed all-dielectric laser-driven undulator for the generation of coherent short wavelengths and explore the required electron beam parameters for its operation. The key concept for this laser-driven undulator is its ability to provide phase synchronicity between the deflection force from the laser and the electron beam for a distance that is much greater than the laser wavelen...

We report experimental studies of the effect of undulator tapering on superradiance in a single-pass highgain free-electron laser (FEL) amplifier. The experiments were performed at the Source Development Laboratory (SDL) of National Synchrotron Light Source (NSLS). Efficiency was nearly tripled with tapering. Both the temporal and spectral properties of the superradiant FEL along the uniform an...

The first lasing in the mid infrared (IR) at the ELBE FEL [1, 2] allows us to specify the parameters of an additional undulator for longer wavelengths to complement the U27 undulator which is useful up to about 25 microns at most. In the longer wavelength range FELs constitute a unique radiation source with appealing properties. Radiation quanta in this range are appropriate for the lowenergy s...

We review the coherence properties of the self-amplified spontaneous emission (SASE). Temporally, SASE is similar to the spontaneous undulator radiation except that the spectral bandwidth is about ten times narrower compared with typical undulator radiation. The situation is quite different in the transverse dimension, where SASE is fully coherent. INTRODUCTION Several laboratories are pursuing...

Five SASE FEL’s and five spontaneous undulator systems are proposed for the FEL lab at TESLA. The SASE systems are the longest. Their total length can be in excess of 300m. In order to keep the beam size small over the whole system a strong focusing FODO lattice is needed. The parameters for the X-ray FEL’s allow to separate between the undulators and the strong focusing. This has the advantage...