ANL, Argonne
X-ray free electron lasers (FELs) are well suited to pursue a long-standing goal of studying matter in a transient state that is far from equilibrium. This state often determines the functions of materials and, thus, holds a key to understanding how to control them. The natural time scale for most of the dynamic processes involving atoms is of the order of 100 femtoseconds, and existing x-ray FELs have already surpassed this mark. The natural time scale for dynamic processes driven by electrons is of the order of 100 attoseconds, and this is the next Rubicon for FELs. In this talk I will review the state of the art in generation of femtosecond x-ray pulses using FELs and will discuss a number of new ideas en route to sub-femtosecond x-ray pulses.
DESY, Hamburg
The Free Electron Laser in Hamburg (FLASH) is a SASE FEL user facility and in addition serves as a prototype for the European XFEL. The recent upgrade of FLASH with a higher harmonic RF module opens a new possibility for ultra-short low charge operation. The advantage of small transverse emittance at low charges can be used only with strong, linearized bunch compression. At this report we consider simulations of the beam dynamics at low charges and estimate the expected properties of the radiation at FLASH and the European XFEL. We present first experimental results at FLASH.
SLAC, Menlo Park, California
There is a growing interest in the generation and characterization of femtosecond and sub-femtosecond pulses from linac-based free-electron lasers (FELs). In this paper we study a simple longitudinal transformation* for measuring a very short electron bunch. We show that this method can be applied in a straightforward manner at x-ray FEL facilities such as the Linac Coherent Light Source by slightly adjusting the second bunch compressor followed by running the bunch on an rf zero-crossing phase of the final linac. After taking into account the linac wakefield, we find the condition under which the final beam energy spread corresponds directly to the compressed bunch length. When used in conjunction with a high-resolution electron spectrometer, this method potentially reveals temporal information of femtosecond and sub-femtosecond electron bunches used by such FELs.
* K. Ricci and T. Smith, Phys. Rev. ST-AB 3, 032801 (2000).
ELETTRA, Basovizza
University of Nova Gorica, Nova Gorica
FERMI@Elettra will have two different seeded FELs for covering the spectral range between 80 and 4nm. The shorter wavelength FEL, namely FEL-2, will cover the spectral range between 20 and 4 nm, and will be based on a double cascade high gain harmonic generation scheme. Moreover, the system has been designed to allow the implementation of other seeding schemes, like seeding with high-order harmonics generated in gas and echo-enhanced harmonic generation (EEG). In this work, we present the studies on the possible implementation on FERMI of the EEHG, reporting about the expected performance. The number of photons per pulse and the FEL bandwidth are calculated by means of time dependent start-to- end simulations.
Diamond, Oxfordshire
JAI, Oxford
The production of short pulse radiation of 1fs or below would open up many new areas of research. Saldin et al recently proposed a scheme to generate such pulses, in which a laser pulse consisting of only a few optical cycles is used to give a short energy chirp to the electron bunch and uses a tapered undulator to compensate the chirped region. In this paper we study the application of this scheme to a soft x-ray free electron laser, including the results of fully start to end simulations and an assessment of the sensitivity to jitter.
SINAP, Shanghai
A SASE experiment has been done at SDUV-FEL(SINAP), the spontaneous radiation and exponential growth regime are observated. The results are compared with the SASE theory.
ISIR, Osaka
Femtosecond electron beam, which is essential for pump-probe measurement, was generated with a 1.6-cell S-band photocathode rf gun. The rf gun was driven by femtosecond UV laser pulse (266 nm), which was generated with third-harmonic-generation (THG) of Ti:Sapphire femtosecond laser (800 nm). The longitudinal and transverse dynamics of the electron bunch generated by the UV laser was investigated. The bunch length was measured with the dependence of energy spread on acceleration phase in a linac, which was set at the downstream of the rf gun. Transverse emittance at the linac exit was also measured with Q-scan method.
UCLA, Los Angeles, California
SLAC, Menlo Park, California
Success in commissioning the world's first x-ray (0.15-1.5 nm) free electron laser (FEL) - the LINAC Coherent Light Source (LCLS) - at SLAC National Accelerator Laboratory opens the gate for new science. Further improving the FEL spectrum bandwidth, shortening the FEL pulse temporal duration, and generating even higher energy x-ray photons are urged by various potential users. In this paper, we study the possibility of generating femtosecond duration X-ray pulses with a variable photon energy from 1.5 to 48 keV, using an electron beam with the same characteristics of the LCLS beam, and a planar undulator with additional focusing. We assume that the beam energy can be changed, and the undulator has a variable gap, allowing the undulator parameter to be changed from zero to a maximum value. It is assumed to be operated in an ultra-low charge and ultra-short pulse regime.
PSI, Villigen
DESY, Hamburg
Electro Optical (EO) sampling is a promising non-destructive method for measuring ultra short (sub picosecond) electron bunches. A prototype of a compact EO bunch length monitor system for the future SwissFEL facility was designed and built at PSI. Its core components are an optical setup including the electro optically active crystal and an Ytterbium fiber laser system which emits broadband pulses at 1050nm. The new monitoring system is described in detail and first experimental results from the SLS injector are presented.
DESY, Hamburg
PSI, Villigen
Electro Optical (EO) sampling is a promising non-destructive method for measuring ultra short (sub-ps) electron bunches. The FEMTO slicing experiment at the Swiss Light Source modulates about 3 pC of the 5 nC electron bunch longitudinally. The coherent synchrotron radiation (CSR) emitted by this substructure was measured in a single shot EO technique in gallium phosphide (GaP) using pulses from an Yb fiber laser. The arrival time jitter and the broadening of this ps long structure over several turns of the synchrotron could be measured with sub-ps resolution.
MAX-lab, Lund
The MAX IV injector is funded and under construction. It is designed to drive a Short Pulse Facility generating spontaneous incoherent photon pulses in the keV range with pulse lengths below 100 fs in the first phase of the project. This source will with minor modifications be able to drive a Free Electron Laser down into the soft X-ray region and with an extended energy a full X-ray FEL at 1-2 Å. The key feature of the system is the availability of a 3-3.5 GeV linac, a low emittance photo cathode RF-gun and two bunch compressors including sextupoles for linearization. By extracting pulses of 0.1-0.2 nC charge, normalized emittances below 1 mm mRad and peak currents above 3 kA can be achieved. Such pulses are very well suited for a FEL facility. We describe the MAX IV injector system and discuss the options and perspectives for an X-ray FEL at the MAX IV facility.
European XFEL GmbH, Hamburg
DESY, Hamburg
In this paper we describe a measurement technique capable of resolving femtosecond X-ray pulses from XFEL facilities. Since these ultrashort pulses are themselves the shortest event available, our measurement strategy is to let the X-ray pulse sample itself. Our method relies on the application of a "fresh" bunch technique, which allows for the production of a seeded X-ray pulse with a variable delay between seed and electron bunch. The shot-to-shot averaged energy per pulse is recorded. It turns out that one actually measures the autocorrelation function of the X-ray pulse, which is related in a simple way to the actual pulse width. For implementation of the proposed technique, it is sufficient to substitute a single undulator segment with a short magnetic chicane. The focusing system of the undulator remains untouched, and the installation does not perturb the baseline mode of operation. We present a feasibility study and we make exemplifications with typical parameters of an X-ray FEL.