Generation of intense attosecond x-ray pulses using Echo-Enabled Harmonic

Generation (EEHG) FEL

Dao Xiang, SLACin collaboration with Z. Huang and G. Stupakov

Presented at the “Workshop on X-ray science at the femtosecond to attosecond frontier, UCLA, May,18~20, 2009”

dxiang@SLAC.Stanford.EDU

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� Outline

� Principles of EEHG FEL

� Applications in generation of attosecond x-ray pulses

� Simulations of EEHG FEL

� Fermi@Elettra FEL

� LBNL FEL

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� Related publications� G. Stupakov, Using the beam echo effect for generation of short-wavelength radiation, Phys. Rev. Lett, 102, 074801 (2009).

� D. Xiang and G. Stupakov, Echo-enabled harmonic generation free electron laser, Phys. Rev. ST-AB, 12, 030702 (2009).

� D. Xiang and G. Stupakov, Running Shanghai soft x-ray FEL with the EEHG scheme, SLAC-PUB-13475, (2008).

� Z. Huang, D. Ratner, G. Stupakov and D. Xiang, Effects of energy chirp effect on echo-enabled harmonic generation FELs, SLAC-PUB-13547, (2009)

� D. Xiang, Z. Huang and G. Stupakov, Generating intense attosecond x-ray pulses using UV-laser-induced microbunching in electron beams, SLAC-PUB-13533, (2009)

� D. Xiang and G. Stupakov, Tolerance study for the echo-enabled harmonic generation free electron laser, Proceedings of PAC09, (2009).

� D. Xiang and G. Stupakov, Coherent soft x-ray generation in the water window using the EEHG scheme, Proceedings of PAC 09, (2009).

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� Principles of HGHG FEL

� Energy modulation in the modulator

� Energy modulation converted to density modulation

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� Principles of HGHG FEL

� Limitation:

Modulator exit

Modulator exit

Chicane exit

Chicane exit

Current distribution

Current distribution

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� The role of a virtual collimator

� Separated energy bands increase the harmonic numbers

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� How to generate separated energy bands?

� Using strong dispersion to generate separated energy bands

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modulator exit

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� The principles of EEHG FEL

classic HGHG FELEEHG FEL

1/3nb n−

� Key advantageSeparated energy bands Separated current bands

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� Steady-state simulation� Fermi@Elettra FEL (240 nm ->10nm)

Main parametersBeam energy: 1.2 GeV

Energy spread: 150 keV

Emittance: 1.5 mm mrad

Peak current: 800 A

Run 1 Run 2 Run 3

A B C

A B C

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� Time-dependent simulation� LBNL soft x-ray FEL (190nm -> 3.8 nm)

Longitudinal phase space

Slice energy spread Current

*Courtesy of J. Qiang and A. Zholents

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� Time-dependent simulation� LBNL soft x-ray FEL (190nm -> 3.8 nm)

Power profiles Spectrum

Phase space Bunching factor evolution Power evolution

Bandwidth: 2.7e-4!

Close to Fourier transform limit.

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� Generating attosecond x-ray pulse using EEHG FEL� Harmonic extension by bunch compression

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� Generating attosecond x-ray pulse using EEHG FEL� Single pulse selection with an intense few-cycle laser

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� Generating attosecond x-ray pulse using EEHG FEL

Before dispersion After dispersion After dispersion

1 2

20 as

X-ray power profile

� Allows one to generate 1nm x-ray from a UV seed laser

� Allows one to generate x-ray pulse beyond the atomic unit of time (~24 as)

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� Summary� EEHG is a new promising working scheme

� EEHG allows one to generate high power soft x-ray with narrow bandwidth close to Fourier transform limit directly from a UV seed laser in a single stage

� Combining EEHG with BC allows one to extend harmonic numbers to a few hundred and make possible the generation of an isolated intense attosecond x-ray pulse from a UV seed laser

We thank A. Chao, Y. Ding, J. Wu, D. Ratner, P. Emma, W. Fawley, A. Zholents, S. Reiche, M. Borland for helpful discussions.

Thanks!