seeding of free electron lasers by various techniques a. meseck

Seeding of free electron lasers by various techniquesA. Meseck

*CLASSE-Seminar Nov. 2009 A. Meseck


Synchrotron RadiationTHz


Synchrotron Radiation Sources


Wiggler and Undulator TrajectoryUndulatorparameter Res. Wavelength:


FEL- InteractionInterchange between electron beam and radiation field:


FEL- Equation of Motion


Amplification ( Low Gain ) The amplification of radiation intensity depends on the electron density.

For small electron densities the amplification per turn is small.

For > 0 a net intensity amplification is expected.


Madey -Theorem:The amplification (Gain) is proportional to the negative derivative of the resonance-curve of the spontaneous undulator spectrum. Low Gain


Low Gain FEL


JLAB ERL-FEL


Mirrors for FELs


High Gain - SASE FEL Extremely high electron densities lead to a permanent amplification of the radiation intensity. The electrons are bundled into packages: Micro-bunching The electrons radiate coherently.


Spectral Properties of the SASE -FELsZeit [s]


HGHG SASE Power [GW]Spectrum [a.u.]Advantages of Seeding


Short Laser Pulse (Ti:Sa) brilliant electron beamHigh Gain Harmonic Generation (HGHG)*Dispersive sectionRadiator*Developed by L.-H. Yu et al.,BNL Phys. Rev. A44/8 (1991) 5178


Cascaded HGHG-FEL LasersFinal Amplifierr1= s/n1r2= s/n1 /n2f= r2


Down-conversion of the seeding wavelength to the desired wavelength.

With fresh bunch technique - Classical HGHG a) with final amplifierb) with an extended last radiator

Without fresh bunch technique - Modulator cascade - Radiator cascade- Combination of modulator and radiator cascade - Superradiant cascade Cascading towards < 1nm


Imprinted energy modulation Energy modulationOutput powerTotal energy spreadin radiator Dispersion chicane modulator and radiator



The seeded bunch part is no longer suitable for a further seeding process .Use a long bunch and shift interaction region for each stage2nd StageFinal Amplifier1st StageElectron bunchseed


Ensure that the phase correlation and pulse length are conserved!

the shot-noise effects are suppressed!* E. Saldin et a., Opt. Comm. 202 (2002) 169 Limits the total harmonic number

High seed power required


Classical High-Gain Harmonic-Generation Cascade using Fresh Bunch Technique and Final AmplifierBessy FEL : LE-Line


Classical High-Gain Harmonic-Generation Cascade using Fresh Bunch Technique ChicaneChicaneFB-ChicaneSTARS


Modulator Cascade


Split Modulators Cascade


Split Modulators Cascade


Modulator Cascade ECHO Scheme Modulator 1 + Chicane 1Modulator 2 + Chicane 2


Modulator Cascade ECHO Scheme Modulator 1 + Chicane 1Modulator 2 + Chicane 2


Radiator Cascade


Modulator and Radiator Cascade ** DEVELOPMENTS IN CASCADED HGHG-FELsB. Kuske , A. Meseck, http://accelconf.web.cern.ch/AccelConf/FEL2008/papers/tupph058.pdf


Superradiant Radiator Cascade






The ratio between superradiance parameter S = s Nw / lband the slippage parameter k = lc /lb(bonifaccio-definitions) is the key-parameter.

If the slippage is too small (=> short wavelength), there is no benefit from the superradiant pulse for harmonic generation. Limit of Superradiant cascades


With fresh bunch technique- Classical HGHG a) with final amplifierb) with an extended last radiator

Without fresh bunch technique - Modulator cascade - Radiator cascade- Combination of modulator and radiator cascade

- Superradiant cascade

Cascading towards < 1nmnoise-amplification => HHG seeds ?Increased energy spread too small slippage (=> short wavelength)DEVELOPMENTS IN CASCADED HGHG-FELsB. Kuske , A. Meseck, http://accelconf.web.cern.ch/AccelConf/FEL2008/papers/tupph058.pdf


40nm800MeV-1200 MeVs=40nms=40nms=20nms=10nmExtension: Classical HHG Seeding


40nm800MeV-1200 MeVs=40nms=40nms=8nmExtension of Classical HHG Seeding II


calibration and OTR screens on7Match and 3SUND1ORS Experiment at FLASH*OTR screens on 2SUND2


ORS Experiment at FLASH*


FROG Trace, ORS Experiment


ERL driven Seeded FELs?


Cornell-ERL Mode A : X-ray


Cornell-ERL Mode A: Soft X-ray


Mode A: Soft X-ray ; Higher Current

Bunch Compression


Cornell-ERL Mode C: Soft X-ray


Cornell-ERL Mode D: Soft X-ray Space chargedominated beam


Seeding Example Mode D- Seed powerHHG-Seed?


Mode D- Seed power and Bunching (funda.)


Mode D- Energy spread and Bunching (funda.)


Coherent EmissionDetermined by the desired wavelength range,L .Bunching depends mainly on energy deviation.Bunching at the entrance of the radiator of thesecond stage of STARS with and without space charge force.


SummarySeeded FELs providereproducible, stable radiation (in terms of wavelength and Intensity)better control on pulse shape and pulse durationtransverse and longitudinal coherence

Short wavelength seeds (HHG) with high Intensities are still not state-of-the-art=> Several cascading scheme, e.g. HGHG, modulator and/or radiator cascades, are proposed or already under construction

Seeding can also be used for beam diagnostics, ORS

A seeded FEL can also be driven by an ERL

seeding of free electron lasers by various techniques a. meseck

Documents

amplification gain

meseck modulator cascade

mesecklow gain fel

meseckhigh gain sase

high electron densities

meseckamplification

long bunch

electron density