x-ray free electron laser seeded by ir laser driven high -order...

JuhaoJuhao Wu Wu LINAC Coherent Light Source,LINAC Coherent Light Source,

SLAC National Accelerator Laboratory SLAC National Accelerator Laboratory Paul R. BoltonPaul R. Bolton

Photo Medical Research Center,Photo Medical Research Center,Japan Atomic Energy Agency, JapanJapan Atomic Energy Agency, Japan

XX--ray Free Electron Laser seeded ray Free Electron Laser seeded by by irir laser driven highlaser driven high --order order

harmonic generationharmonic generation

Talk given at UCLA Workshop on X-ray Science at the Femtosecond to Attosecond Frontier, May 18th ~ 20th , 2009

http://home.physics.ucla.edu/calendar/Workshops/CFC _FEL_2009/index.html

May 18-20, 2009UCLA Workshop on X-ray Science

Juhao Wu [email protected]

Smaller and Faster

Bridge the High-order Harmonic Generation (HHG) gro up and seeded Free Electron Laser (FEL) group

One of the scientific research frontiers



Much higher brightness and fluxFree Electron Lasers (from IR to X-ray) Storage rings (Terahertz)

Sources exploiting coherent emission :

( )( ) ( )[ ]ωω gNgNpP 21 +−=

Shorter Pulse Lengths: Femto (10 -15) and Attosecond (10 -18)

Future of Synchrotron Radiation

Courtesy of F. Sannibale, LBNL

Undulator radiation + feed back (instability) Free electron laser

Start from undulator radiation / shot noise Self-Amplified Spontaneous Emission (SASE) exponential growth

Start from a coherent seed Seeded Free Electron Laser

Free Electron Laser



Different configurations:

Oscillator: close to atomic laser

Difficult to find mirror for short-wavelength

SASE: can reach x-ray

Poor longitudinal coherence

Seeded FEL

No x-ray seed

Harmonic Generation

HG FEL

Free Electron Laser





Experimentally verified advantages:Experimentally verified advantages: [Yu [Yu et al.et al. , , ScienceScience , (2000), , (2000), PRLPRL(2003), Wang (2003), Wang et al.et al. , , Proceedings of FELProceedings of FEL ’’06 (2006)06 (2006)]]

Much better Temporal Coherence; Much better Temporal Coherence; An orderAn order --ofof --magnitude narrower bandwidth;magnitude narrower bandwidth;High signalHigh signal --toto --noise ratio;noise ratio;Central wavelength is controllable, and more stable;Central wavelength is controllable, and more stable;Pulse length is controllable;Pulse length is controllable;

Some more:Some more:Less stringent requirement on Electron Beam Less stringent requirement on Electron Beam EmittanceEmittance ;; [[SchnitzerSchnitzerand and GoverGover , 1985] , 1985]

Short total Short total undulatorundulator lengthlength [[BonifacioBonifacio et al., (1992)] et al., (1992)]

Output power is more stableOutput power is more stable [Wu & Yu, NIMA (2001)] [Wu & Yu, NIMA (2001)]

Tunability [Wang (2007)]

Advantages of a seeded HG FEL



Single stage HG FEL

The dream or the hope of a seeded FEL: transform limited photon beam

L.H. Yu, et al. , Science (2000)

SASE power times 106

L.H. Yu, et al. , PRL (2003)



Seed LaserNonlinear harmonic conversion extends to ~150 nm.

Courtesy of X.J. Wang, BNL



Observed – late 1980’s (MainFray, Rhodes, L’Huillier , Salieres, Agostini, Kulander, Corkum, Kapteyn, Murnane….)

Interaction of intense ir laser pulses with low dens ity gas targets yields coherent harmonics of high order and at high repetition rates xuv & soft xray coherent sources

High-order Harmonic Generation (HHG)



Excitation of e- wavepacket via Optical Field Ionizat ion (OFI)Continuum interaction of wavepacket with strong lase r field (ellipticity dependent continuum dynamics begin at i onization time)Rescattering of wavepacket with parent ion (ir laser c ontrols):

Elastic (e – e) accounts for hot tail of ATI electro n spectra (dephasing collisions)Inelastic (e – 2e) accounts for correlated two-elect ron ejectionRadiative emission (recombination) accounts for HHG

Single active electron model of time-dependent dipo le moment & nonlinear polarizability is then coupled to ioniza tion

Semiclassical, Single Atom, 3-Step Model of HHG: Nonperturbative Nonlinear Optics *

•+ •e-

•-

* P. Corkum PRL 71 ,1994 (’93)



Double slit results using 7 th to 17th harmonic orders (one at a time)

Phase difference integrated over driver pulse duration ,

& maintains fringe visibility

Multiple HHG sources can be phase-locked

Highest orders are most coherent and most synchronous

ρ•δ

•L

( ) ( ) rad 8.021 ≤− tt φφoτ

( ) ( )( )

( )( ) ( ) ( ) ( ) 21212121

212121

;

;,;

;cos2

ββββφφβφ

ρδδρφφ

−≈−+−≡−+≡

<<≡∆

−+∆++≈

oo

ioii

t

bbqtt

qbt

LL

l

ttlkIIIII

HHG Coherence

Zerne et al PRL 79 , 1006 (1997)Gibson et al IEEE J. of Sel. Topics in Quant. Elec. 10 , 1339 (2004))



HHG pulses have attosecondstructure that repeats every half irlaser period

harmonics in a phase-locked ‘cluster’ can add to form a train of attosecond ‘pulselets’ spaced by half the fundamental (ir) period

HHG efficiency has strong ir laser ellipticity (polarization state) dependence (effect of 4% ellipticitycan be two orders of magnitude)

Single pulselet formation can be achieved with adequately short durations of linear polarization

Attosecond Structure

A. L’Huillier, Lund Group Website and Lopez-Martens et al PRL 94 , 033001 (2005)



HHG Summary

HHG seeding of FEL can be done using ‘plateau’harmonic orders that are generated with modest laser and gas target parameters

Other HHG experts are considering seeding applications to FELs (eg. for 4GLS & ARC-En-CIEL)

Proof-of-principle seed investigation neededStart with time-integrated measurementsOptimize HHG efficiency for specific order(s)Subsequent investigations address temporal resolution and pulse train control (# of pulselets)



Proof-of-principle Experiment

HHG seeding with the 5 th harmonic ( 800 nm 160

nm)[Collabration between Japan and France ]G. LAMBERT et al, Nature Physics 4 , 296 (2008)



Proof-of-principle Experiment

HHG seeding with the 5th harmonic [Collabrationbetween Japan and France ]

G. LAMBERT et al, Nature Physics 4 , 296 (2008)

HHG seed on LCLS-type electron beam in LCLS-type injector / accelerator / undulator system

HHG seed is attractive, being considered by a few laboratories over the world

Ultrashort

VUV to soft x-ray

Supperradiance mode

HHG-HGHG with LCLS-type electron beam FELUltrashort

Hard x-ray

Powerful

ProposalProposal




HHG Seeded HG FELHHG seeded cascaded HGHG FEL (Cascade from VUV to x -ray): use a UV laser produced by harmonic generatio n (HHG); short pulse (10s fs) seeded FEL + harmonic generation X-ray

Due to slippage (light travels fast than the electr ons) attosecond pulselet can be smeared soon

Wu-Bolton-Murphy-Zhong, App.Phys.Lett., (2007)

Wu-Bolton, FEL’06, p.186 (2006).


Ignoring the attosecond structure

Cascaded HGHG 30 nm 0.3 nm n = 100

Noise degradation seed 5 MW noise << 0.5 kW

HHGHHG--HGHG FELHGHG FEL





19

Starting from conventional laser requires stringent noise-to-signal ratio due to n2 amplification. Hand waving argument on the spectrum contents in the HG FEL:

Initial laser seed phase imperfectness imprints on th e electron beam energy modulation

n th –harmonic generation, phase multiplication n

Yet, a more rigorous discussion about the noise, on e has to consider the noise inside the seeded FEL bandwidth , but not all the SASE which spreads out in a much la rger bandwidth [ Wu-Bolton-Murphy-Zhong, Appl. Phys. Lett. (2007) ]

Noise in HG FELNoise in HG FEL

( ) ( )[ ]

( ) ( )[ ] 4])sin[()()1()]sin(sin[

4])sin[()()1()]sin(sin[

22201

2201

αααωααω

αααωααω

nnJnJtmnnJtntn

JJtmJtt

mm

m

mm

m

≈⇒Ω+−=Ω+

≈⇒Ω+−=Ω+

∑

∑

∞

−∞=

∞

−∞=

HHG seeding can start from EUV 30 nm, yet weak

Conventional laser Ti:Sapphire seed at 240 nm

Comparison of two approachesComparison of two approaches

M. Gullans et al, Optics Communications 274 , 167 (2007)





HHG seeding requires noise-to-signal (NTS) ratio of 1/1000

Conventional laser asks NTS 1/50,000 n2 dependence

21

Comparison of two approachesComparison of two approaches

M. Gullans et al, Optics Communications 274 , 167 (2007)


Question: in the first approach, HHG takes care of 240 nm 30 nm; while in the second approach, HG FEL takes care of the 240 nm 30 nm. In generating 3.75 nm HG FEL, the total harmonic up-conversion n = 240/3.75 = 64 in both cases, so can we conclude the same noise amplification as n2 = 4096?

Well, HHG scheme does not show this n2 amplificationIntroducing phase noise in the ir laser, (equivalent a t the 240 nm seed)

Investigate the spectrum deviation in the HHG

Noise in HHGNoise in HHG

)]( )(sin[)( 0)(

0

220 tstteEtE tt

s αωτ +−= −−

)(

)()()(

ωωωωη

I

II s −=

B. Sheehy et al, Nucl. Instrum. Methods Phys. Res. A , 593, 21(2008)


HHG scheme does not show this n2 amplification

Noise in HHGNoise in HHG

B. Sheehy et al, Nucl. Instrum. Methods Phys. Res. A , 593, 21(2008)



Generation of powerful hard x-ray ultrashort laser pulses in a single-pass free-electron laser

Schroeder, et al., J. Opt. Soc. Am. B, 2002 two stage chirped pulse compression

Emma et al. PRL, 2004 thin foil with slit to spoil most of the electrons but the middle slice Attosecond pulse

Saldin et al., Opt. Commun. 2004 undulator tapering together with electron chirp in the electron bunch best slice

Zholents et al., PRL 2004 Laser interacts with electron pulse to slice ultrashort pulse

24

Harmonic Generation Free Electron Laser





Chirps in a seeded Free Electron Laser (FEL) in general

Frequency chirp along the seed pulse

Energy chirp along the electron bunch

Intrinsic frequency chirp developed during FEL process

Interplay of the chirps

ABCD formalism

High-order Harmonic Generation (HHG) seed for attosecond pulse

Ultrashort, VUV to soft x-ray, attosecond pulse train (APT)

smearing of APT and APT restoration

LCLS-type high brightness electron bunch seeded by HHG Ultrashort, powerful, hard x-ray FEL

Interplay of the chirps in a seeded FEL and chirped pulse compression

Ellipse evolution

Wu-Murphy-Emma-Wang-Watanabe-Zhong, J. Opt. Soc. Am. B 24 , 484 (2007)





27

APT HHG seeded FEL

Wu-Bolton-Murphy-Wang, OPTICS EXPRESS 15, 12749(2007)


Transform limited bandwidth achieved with narrow seed. Transform limited bandwidth achieved with narrow seed.

Spectral Control by the Seed Laser

3 ps seed laser 6 ps seed laser

X.J. Wang J.B. Murphy, et al., Source Development L ab(SDL)/NSLS/BNL, 2008

Wu-Murphy-Emma-Wang-Watanabe-Zhong, J. Opt. Soc. Am. B 24 , 484 (2007)


HHG Seeded HG FEL

Great progress made in laser seeded harmonic FEL, i t will be the workhorse in VUV and soft X-Ray regimes . Laser seeded Harmonic FEL

Laser seeded harmonic is tunable.FEL spectral can be controlled by the seed laserReduce the jitter between the seed and the FEL, hel pful for pump-probe experiment

Higher harmonic in single stage HG FELCascadingChirped pulse compression for few-cycle ultrashortcoherent x-raySuperradiance [Wu-Bolton-Murphy-Wang, OPTICS EXPRESS 16 , 3255(2008)]



13 nm Seeded HG FEL

We keep the ir component, and focus on the 59 th

harmonics with 5 adjacent harmonics in the simulati onAssuming ir laser (790 nm) to be 40 mJ to optimize fo r the 13 nm, which is about 40 nJ [ OPTICS LETTERS 32, 722 (2007) ]

We assume the 5 adjacent harmonics are in phase and the intensity is about 80% of that of the 13 nm har monic [APPLIED PHYSICS LETTERS, 84, 4 (2004)]Convert into peak power, and assuming loss (1-order of magnitude) due to various reasons, we assume 13 nm has peak power of 0.2 MW, and the other 4 adjacent harmonics have 0.16 MW peak power.The ir is assumed to have 2 GW peak power





13 nm Seeded HG FEL

Illustration of the seed laserWith the ir

Without the ir(attosecond pulse train)



13 nm Seeded HG FEL

FEL is a narrow bandwidth filter, so even though th e harmonics are in group of a few harmonics, only one is being amplified.It might be interesting trying to get one attosecon dpulselet from the APT

One might consider manipulating the electron bunch energy profile, in particular, chirpHowever, due to slippage, the shortest time scale should be on the order of fs


13 nm Seeded HG FEL

The time-domain adjacent attosecond pulselets (AP) are separated by half of the ir laser wavelength

Requirement 1: The energy chirp should be large enough, so that the relative energy difference betw een the adjacent APs should be larger than a few times of ρρρρRequirement 2: Yet, the energy chirp should be smal l enough so that along the electron bunch, no frequen cy-domain adjacent harmonics can be excited

For example of seeding with 13 nm, we have ρρρρ ~ 2.3E-3. For ir at 768 nm, requirement 1 sets the chirp to be larger than 6 (mm -1), and requirement 2 sets the chirp to be smaller than 11 (mm -1) – seems to have solutionThis is very larger chirp indeed – about 5 MeV per 40 0 nm


13 nm Seeded HG FEL

Convention RF is impossible to provide such a large chirp along the electron bunchOne might consider to use laser to modulate the electron bunchHow about the ir laser generating the HHG

In the following, we assume the ir laser is at 768 n mThe 59th harmonic which is about 13 nm is accompanied with the 55 th, 57th, 61st, 63rd harmonicsWe use LCLS measured beam parameters, emittance0.5 mm-mrad, peak current 1 kA, energy 2 GeV, and relative energy spread 1.0E-4.



13 nm Seeded HG FEL

Schematic plot

Genesis simulation for the above scheme

Electron Electron

PhotonPhoton

ir Laser local chirp, energy modulation buncher

13 nm

3.25 nm



Energy modulation at ir laser wavelength

13 nm Seeded HG FEL

Chirp about 11 mm -1

spectrum





Evolution in the modulator 13 nm Seeded HG FEL

spectrum power

The final 3.25 nm FEL



3.25 nm FEL

spectrum power

We might finally get sub-fs pulse

Acknowledgement

Thanks orgnizers for kind invitationThanks for collaborators





[1] J. Wu and L.H. Yu, “Eigenmodes and mode competition in a high-gain free-electron laser including alternating-gradient

focusing”, Nucl. Instr. and Meth. A 475, 79 (2001).

[2] J. Wu and L.H. Yu, “Coherent hard X-ray production by cascading stages of High Gain Harmonic Generation”, Nucl. Instr. and

Meth. A 475, 104 (2001).

[3] L.H. Yu and J. Wu , “Theory of high gain harmonic generation: an analytical estimate”, Nucl. Instr. and Meth. A 483, 493

(2002).

[4] L.H. Yu and J. Wu , “Simulations for the FERMI@ELETTRA proposal to generate 40- and 10-nm coherent radiation using the

HGHG scheme”, Nucl. Instr. and Meth. A 507, 455 (2003).

[5] J.B. Murphy, J. Wu, X.J. Wang, and T. Watanabe, “Longitudinal Coherence Preservation and Chirp Evolution in a High Gain

Laser Seeded Free Electron Laser Amplifier”, Brookhaven National Laboratory Report BNL-75807-2006-JA, and SLAC-

PUB-11852 (2006)

[6] J. Wu, P.R. Bolton, “Coherent X-Ray Production by Cascading Stages of High Gain Harmonic Generation Free Electron

Lasers Seeded by IR Laser Driven High-Order Harmonic Generation ”, Proceedings FEL’06 p. 186 (2006).

[7] J. Wu, P.R. Bolton, J.B. Murphy, and X. Zhong, “Free electron laser seeded by ir laser driven high-order harmonic

generation”, Appl. Phys. Lett. 90, 021109 (2007).

[8] J. Wu, J.B. Murphy, P.J. Emma, X.J. Wang, T. Watanabe, and X. Zhong, “Interplay of the chirps and chirped pulse

compression in a high-gain seeded free-electron laser”, J. Opt. Soc. Am. B 24, 484 (2007).

[9] J. Wu, P.R. Bolton, J.B. Murphy, and K. Wang, “ABCD Formalism and Attosecond Few-cycle Pulse via Chirp Manipulation of

a Seeded Free Electron Laser”, Optics Express 15,12749 (2007).

[10] J. Wu, J.B. Murphy, X. Wang, and K. Wang, “Exponential growth, superradiance, and tunability of a seeded free electron

laser”, Optics Express 16, 3255 (2008).

[11] J. Wu, A.W. Chao, and J.J. Bisognano, “The Electron Bunch Initial Energy Profile on a Seeded Free Electron Laser

Performance”, Proceedings LINAC’08, TUP049 (2008).

[12] A.A. Lutman, G. Penco, P. Craievich, and J. Wu, “Impact of an initial energy chirp and an initial energy curvature on a

seeded free electron laser: the Green’s function”, J. Phys. A 42, 045202 (2009).

[13] A.A. Lutman, G. Penco, P. Craievich, and J. Wu, “Impact of an initial energy chirp and curvature on a seeded free electron

laser II: free electron laser properties”, J. Phys. A 42, 085405 (2009).

Collaborators and References

x-ray free electron laser seeded by ir laser driven high -order...

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