Attosecond X-ray free electron laser

For a real, meaningful pump-probe experiment with attosecond temporal resolution, an isolated attosecond pulse is in demand. In this vein we report the generation of an isolated ~ 148 attosecond pulse duration radiation pulse at 0.1 angstrom wavelength using current enhanced self-amplified spontaneous emission free electron laser. We consider the 10-GeV PAL-XFEL e-beam for enhanced self-amplified spontaneous emission (ESASE) scheme. In ESASE, X-ray SASE FEL is combined with a femtosecond laser system. An 800 nm wavelength, 5 fs FWHM carrier envelope phase stabilized laser was employed in ESASE scheme.


Introduction
Current synchrotrons are limited up to picosecond time duration x-ray pulses, which are not capable to follow the electron dynamics in atoms, molecules and nanoscopic systems.These investigations demand tools with attosecond temporal and nanometer spatial resolutions.
Future hard x-ray FEL facility either have been proposed or are under construction [1][2][3].The first successful single pass SASE FEL at 32 nm with a pulse duration of 25 femtosecond FWHM has been reported in 2006 [4].Later the operation at 13.7 nm was reported [5].In the saturation regime, the peak energy of 170 µJ was obtained.The average energy per pulse reached 70 µJ.The pulse duration was in the region of 10 femtosecond, and the peak power of 10 GW was achieved.SPring-8 Compact SASE source (SCSS) in Japan demonstrated the saturation at wavelengths ranging from 51 to 61 nm with a maximum pulse energy of 30 µJ from a 55 m long compact SASE source operating at a low acceleration energy of 250 MeV [1].In the hard x-ray region, LCLS at Stanford Linear accelerator (SLAC) is the first hard x-ray FEL machine, which is in operation since 2009.This facility has tunable radiation wavelength from 2.2 to 0.12 nm by varying the electron energy in the range of 3.5 to 15 GeV [6].The interaction of carrier envelope phase (CEP) stabilized few-cycle laser with electron-bunch in a wiggler magnet with single or double period prior to x-ray undulator in SASE FEL was employed.It was noticed that the interaction plays a vital role for the generation of isolated attosecond x-ray pulses with FEL [7-9]

ESASE scheme for hard X-ray pulse generation
We consider a simpler enhanced SASE scheme as shown in Fig. 1.An electron beam from a linear accelerator is sent to a double-period wiggler magnet.At the same time, a few-cycle CEP This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.EPJ Web of Conferences stabilized laser co-propagates to induce the energy modulation in the electron beam inside the wiggler.Only small a longitudinal section of the electron beam interacts with the las beam now enters into a chicane, which introduces dispersion in a chicane: the higher the electron energy is, the shorter it travels.In general, this leads to the density modulation, producing the microbunching of the electrons at a laser wavelength spacing and periodic current peaks.electron-bunch enters into a long undulator to produce perfect microbunches and radiation at x wavelength via standard SASE process.3 Isolated Attosecond pulse generation

Generation of single current spike by energy and spatial profile of e
We have studied the effect of laser wavelength on the current profile to obtain an attosecond hard x-ray pulse, using electron beam parameters similar to those of the electron beam of the PAL XFEL [3]: a beam energy of 10 GeV, a total electron-bunch charge 0.2 nC, a beam normalized emittance of 0.5 µm-rad, an electron-bunch average-current of 3 kA or higher.A duration 7.5 femtosecond FWHM is used to modulate the electron beam energy.The laser is CEP stabilized.The beam waist at focus is 250 µm.The wiggler magnet is a two 1.1459 Tesla and λ w = 55 cm.The electron beam properties a dimensional particle tracking code, ELEGANT [10].
Three different energy distributions of electron-bunch are µm (~ 66 fs) long electron-bunch with an average current of 3 kA (Fig.
long electron-bunch with an average current of 4 kA (Fig.
electron-bunch with an average current 6 kA (Fig. 2 generated by using ELEGANT code.The momentum compaction factor R good quality of electron beam and the size of chicane.These three electron distributions are utilized for ESASE scheme.

Conferences
propagates to induce the energy modulation in the electron beam inside the wiggler.Only small a longitudinal section of the electron beam interacts with the laser.The electron beam now enters into a chicane, which introduces dispersion in a chicane: the higher the electron this leads to the density modulation, producing the wavelength spacing and periodic current peaks.Finally, the bunch enters into a long undulator to produce perfect microbunches and radiation at x-ray ESASE scheme for attosecond pulse generation.

Attosecond pulse generation energy and spatial profile of e-bunch
We have studied the effect of laser wavelength on the current profile to obtain an attosecond hard parameters similar to those of the electron beam of the PAL XFEL bunch charge 0.2 nC, a beam normalized emittance of current of 3 kA or higher.A 1200 nm, ~ 13 GW laser, pulse is used to modulate the electron beam energy.The laser is CEP m.The wiggler magnet is a two-period magnet with B 0 = = 55 cm.The electron beam properties are calculated by using the six- bunch are studied which are as follows: (1) ~ 20 bunch with an average current of 3 kA (Fig. 2

Single isolated Attosecond radiation pulse generation
We present x-ray radiation for three different electron section.The electron bunch is sent into a 100-m long undulator modulated electron bunches in the undulator is computed b FEL code GENESIS [11].A 1200 nm and 7.5 femtosecond FWHM laser have modified these bunches.Since the SASE radiation is based on the build different behaviors, different saturation points, and different oscillation pattern.
Figure 3 (a) shows the plot of the radiation power generated at z = bunch of 3 kA.The typical peak power is 10 GW. Figure power generated at z = 55 meter for an electron-bunch of on average.Figure 3 (c) shows the plot of the radiation power measured at z = 34 meter for an average current of 6 kA.For this electron beam only a 34 meter long undulator produce the saturated power.The pulse duration of this peak is ~ 146 attosecond FWHM and the typical peak power is 58 GW.The saturation position is the point where the exponential growth of the radiation power stops.The space charge effects are severe in the low energy e account in the gun part of PAL-XFEL.10 GeV is quite high energy so that space charge effects are not so important

Summary
The optimization of laser parameters (wavelengths and pulse durations) shows that 1200 nm and 7.5 femtosecond FWHM and 0.2 mJ are optimal laser parameters for producing a single attosecond current peak with a high contrast for a given 10 GeV electron beam of the PAL XFEL.It is demonstrated in simulation that the manipulation of electron energy distribution can produce a high contrast single peak in an electron bunch.Using the PAL XFEL parameters, we have shown that an isolated 146 attosecond, 58 GW peak at 0.1 nm is expected to be generated in a 34-meter long undulator Conferences DOI: 10.1051/ C Owned by the authors, published by EDP Sciences,