LONGITUDINAL COHERENCE IN AN FEL WITH A REDUCED LEVEL OF SHOT NOISE

Abstract For a planar free electron laser (FEL) configuration we study self-amplified coherent spontaneous emission driven by a gradient of the bunch current in the presence of different levels of noise in bunches. We calculate the probability density distribution of the maximum power of the radiation pulses for different levels of shot noise. It turns out that the temporal coherence quickly increases as the noise level reduces. We also show that the FEL based on coherent spontaneous emission produces almost Fourier transform limited pulses and the time-bandwidth product is mainly determined by the bunch length and the interaction distance in an undulator. We also propose a scheme that permits the formation of electron bunches with a reduced level of noise and a high gradient of the current at the bunch tail to enhance coherent spontaneous emission. The presented scheme uses effects of noise reduction and controlled microbunching instability and consists of a laser heater, a bunch compressor, and a shot noise suppression section. The noise factor and microbunching gain of the overall proposed scheme with and without laser heater are estimated

Towards single-cycle attosecond light from accelerators

The Free-Electron Laser (FEL) is a cutting-edge, accelerator-based instrument that has the potential to provide simultaneous access to the spatial and temporal resolution of the atomic world. In a FEL, ultra-short electron bunches from an accelerator are passed through a long undulator magnet to generate coherent light. Recently, scientists from SLAC demonstrated the first generation of attosecond hard X-ray pulses, using the Linac Coherent Light Source. Now, as described in the review article by Alan Mak et al. [1], researchers are proposing developments that will make the FEL a fully coherent, singlecycle (attosecond) X-ray laser. The new concepts build upon a strong nexus between linear accelerators, FELs and quantum lasers, to produce extreme attosecond pulses with controllable waveforms

Attosecond single-cycle undulator light : a review

Research at modern light sources continues to improve our knowledge of the natural world, from the subtle workings of life to matter under extreme conditions. Free-electron lasers, for instance, have enabled the characterization of biomolecular structures with sub-angstrom spatial resolution, and paved the way to controlling the molecular functions. On the other hand, attosecond temporal resolution is necessary to broaden our scope of the ultrafast world. Here we discuss attosecond pulse generation beyond present capabilities. Furthermore, we review three recently proposed methods of generating attosecond x-ray pulses. These novel methods exploit the coherent radiation of microbunched electrons in undulators and the tailoring of the emitted wavefronts. The computed pulse energy outperforms pre-existing technologies by three orders of magnitude. Specifically, our simulations of the proposed Soft X-ray Laser at MAX IV (Lund, Sweden) show that a pulse duration of 50-100 as and a pulse energy up to 5 μJ is feasible with the novel methods. In addition, the methods feature pulse shape control, enable the incorporation of orbital angular momentum, and can be used in combination with modern compact free-electron laser setups

Matter manipulation with extreme terahertz light: Progress in the enabling THz technology

Terahertz (THz) light has proven to be a fine tool to probe and control quasi-particles and collective excitations in solids, to drive phase transitions and associated changes in material properties, and to study rotations and vibrations in molecular systems. In contrast to visible light, which usually carries excessive photon energy for collective excitations in condensed matter systems, THz light allows for direct coupling to low-energy (meV scale) excitations of interest, The development of light sources of strong-field few-cycle THz pulses in the 2000s opened the door to controlled manipulation of reactions and processes. Such THz pulses can drive new dynamic states of matter, in which materials exhibit properties entirely different from that of the equilibrium. In this review, we first systematically analyze known studies on matter manipulation with strong-field few-cycle THz light and outline some anticipated new results. We focus on how properties of materials can be manipulated by driving the dynamics of different excitations and how molecules and particles can be controlled in useful ways by extreme THz light. Around 200 studies are examined, most of which were done during the last five years. Secondly, we discuss available and proposed sources of strong-field few-cycle THz pulses and their state-of-the-art operation parameters. Finally, we review current approaches to guiding, focusing, reshaping and diagnostics of THz pulses. (C) 2019 The Author(s). Published by Elsevier B.V

Giant single-cycle THz pulsesfor pump-probe experiments

Strong-field single-cycle THz pulses are an invaluable tool forprobing and controlling low-energy excitations in matter such asmagnons, plasmons, phonons and Josephson waves. A novel scheme isproposed to generate quasi-half-cycle GV/m THz pulses with a mutlikilohertzrepetition rate. It makes use of coherent spontaneous emissionfrom a pre-bunched electron beam traversing an optimally taperedundulator. The scheme is the further development of the novel conceptof the slippage control in free-electron lasers [T. Tanaka, PRL 114 (2015)044801]. The pump-probe THz/X-ray/optical configuration is discussed

An approach to characterization of the Lorentz transfer function of ESS spoke cavities at FREIA

In this memo we discuss the physics of ponderomotive effects in superconducting cavities and identify the preparations needed to be done for performing measurements of Lorentz transfer functions atthe FREIA laboratory. Specifically, it turns out that we need a stub tuner for increasing the externalquality factor of the spoke cavity in order to be able to measure Lorentz transfer functions. Electronics required for measurements is also discussed.</p

Giant single-cycle THz pulsesfor pump-probe experiments

Strong-field single-cycle THz pulses are an invaluable tool forprobing and controlling low-energy excitations in matter such asmagnons, plasmons, phonons and Josephson waves. A novel scheme isproposed to generate quasi-half-cycle GV/m THz pulses with a mutlikilohertzrepetition rate. It makes use of coherent spontaneous emissionfrom a pre-bunched electron beam traversing an optimally taperedundulator. The scheme is the further development of the novel conceptof the slippage control in free-electron lasers [T. Tanaka, PRL 114 (2015)044801]. The pump-probe THz/X-ray/optical configuration is discussed

Quasi-half-cycle pulses of light from a tapered undulator

Strong-field few-cycle terahertz (THz) pulses are an invaluable tool for engineering highly non-equilibrium states of matter. A scheme is proposed to generate quasi-half-cycle GV/m-scale THz pulses with a multikilohertz repetition rate. It makes use of coherent spontaneous emission from a prebunched electron beam traversing an optimally tapered undulator. The scheme is the further development of the slippage control in free-electron lasers [T. Tanaka, Phys. Rev. Lett. 114, 044801 (2015)]. An explicit condition for the spectral amplitude of undulator radiation and a phase condition for the electron density distribution, required for the generation of desired pulses, are presented. The amplitude condition is met by proper undulator tapering, and a generic optimal undulator profile is found analytically. In order to meet the phase condition, the distance between the adjacent bunches is varied according to the instantaneous resonant undulator wavelength. A 3D analytical theory is complemented by a detailed numerical study based on a direct solution to the 3D wave equation

Giant single-cycle THz pulsesfor pump-probe experiments

Strong-field single-cycle THz pulses are an invaluable tool forprobing and controlling low-energy excitations in matter such asmagnons, plasmons, phonons and Josephson waves. A novel scheme isproposed to generate quasi-half-cycle GV/m THz pulses with a mutlikilohertzrepetition rate. It makes use of coherent spontaneous emissionfrom a pre-bunched electron beam traversing an optimally taperedundulator. The scheme is the further development of the novel conceptof the slippage control in free-electron lasers [T. Tanaka, PRL 114 (2015)044801]. The pump-probe THz/X-ray/optical configuration is discussed