Neil Thompson

Transform-limited X-ray pulse generation from a high-brightness self-amplified spontaneous-emission free-electron laser

A method to achieve high-brightness self-amplified spontaneous emission (HB-SASE) in the free-electron laser (FEL) is described. The method uses repeated nonequal electron beam delays to delocalize the collective FEL interaction and break the radiation coherence length dependence on the FEL cooperation length. The method requires no external seeding or photon optics and so is applicable at any wavelength or repetition rate. It is demonstrated, using linear theory and numerical simulations, that the radiation coherence length can be increased by approximately 2 orders of magnitude over SASE with a corresponding increase in spectral brightness. Examples are shown of HB-SASE generating transform-limited FEL pulses in the soft x-ray and near transform-limited pulses in the hard x-ray. Such pulses may greatly benefit existing applications and may also open up new areas of scientific research.

An XUV-FEL amplifier seeded using high harmonic generation

A detailed design of a free electron laser (FEL) amplifier operating in the extreme ultra violet (XUV) and seeded directly by a high harmonic source is presented. The design is part of the 4th generation light source (4GLS) facility proposed for the Daresbury Laboratory in the UK which will offer users a suite of high brightness synchronised sources from THz frequencies into the XUV. The XUV-FEL will generate photons with tunable energies from 8 to 100 eV at giga-watt peak power levels in near Fourier-transform limited pulses of variable polarisation. The designs of the high harmonic generation (HHG) seeding, FEL amplifier and synchronising systems are presented. Numerical simulations quantify the FEL output characteristics.

Short wavelength regenerative amplifier free electron lasers

In this paper we discuss extending the operating wavelength range of tunable Regenerative Amplifier FELs to shorter wavelengths than current design proposals, notably into the XUV regions of the spectrum and beyond where the reflectivity of broadband optics is very low. Simulation studies are presented which demonstrate the development of good temporal coherence in generic systems with a broadband radiation feedback of less than one part in ten thousand.

A design for the generation of temporally-coherent radiation pulses in the VUV and beyond by a self-seeding high-gain free electron laser amplifier

A proposal for a self-seeding, tunable free-electron laser amplifier operating in the vacuum ultra-violet (VUV) region of the spectrum is presented. Full three-dimensional (3D) modelling of the free electron laser and the optical feedback system has been carried out. Simulations demonstrate the generation of near transform limited radiation pulses with peak powers in the hundreds of megawatts. Preliminary 1D simulations show that by using a similar system it may be possible to extend such operation beyond the VUV to higher photon energies.

High harmonic attosecond pulse train amplification in a free electron laser

It is shown using three-dimensional simulations that the temporal structure of an attosecond pulse train, such as that generated via high harmonic generation in noble gases, may be retained in a free electron laser amplifier through to saturation using a mode-locked optical klystron configuration. At wavelengths of ~12 nm, a train of attosecond pulses of widths ~300 as with peak powers in excess of 1 GW are predicted.

Design for an Infra-Red Oscillator FEL for the 4GLS Energy Recovery Linac Prototype

Publisher Summary This chapter presents the design for an infra-red oscillator free-electron laser (FEL) for the Fourth Generation Light Source (4GLS) Energy Recovery Linac Prototype. The injector of infra-red FEL (IR-FEL) is a photocathode design with a high repetition frequency and the electron bunches are accelerated in a superconducting linac. The FEL wavelength varies between 6μm at beam energy of 30MeV and 2μm at 50MeV. This leads to an extraction efficiency of approximately 0.4% and a full induced energy spread (6σ) in the electron beam of about 4%. This is a minimum requirement for the energy acceptance of the return arc. Insertable scraper mirror outcoupling allows the optimization of the outcoupling fraction as the wavelength range is scanned and the mode size on the mirrors changes. The attraction of 4GLS is the synchronization of multiple sources. It is, therefore, proposed to use the ERLP to undertake the synchronization and timing studies of the ERLP IR-FEL output in conjunction with the outputs of the other ERLP photon sources.

A time-preserving soft X-ray monochromator for a FEL source: design optimisation using Genesis simulations and wavefront propagation

A design concept for a soft X-ray monochromator that can preserve the length of a FEL pulse at the femtosecond level is presented. The design is based around a plane diffraction grating in a classical mount operating in collimated light. Designing the beamline requires a thorough knowledge of the source behaviour, which is achieved by wavefront propagation of the simulations of the FEL output. The effect on the spectral filtering on the pulse profile has been explored and is found to improve the contrast ratio without significantly reducing the peak power.