Attosecond Transient Absorption Spectroscopy of Atoms and ...
Generation of intense attosecond x-ray pulses using Echo...
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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”
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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!