Harmonic lasing in the LCLSII SXR beamline

G. Marcus, Y. Ding, Z. Huang11/21/2013

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Outline

• Motivation

• Beamline geometry

• Steady-state analysis• 3rd harmonic

• Time-dependent GENESIS• 3rd harmonic of Eγ = 1.24 keV• Various configurations (intra-undulator phase shifts)

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Motivation

• Harmonic lasing can be a cheap and relatively efficient way to extend the photon energy range of a particular FEL beamline

• In comparison to nonlinear harmonics, can provide a beam that is more• Intense• Stable• Narrow-band

• Suppression by• Phase shifters• Spectral filtering

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Beamline geometry – nominal layout

Quad Phase shifter Undulator

Modeled in GENESIS using AD parameter in drift

5Insert Presentation Title in Slide Master

Simulation parameters – ideal beam

• e-beam• E = 4 GeV• I = 1.0 kA • εn ~ 0.45 μm

• σE ~ 500 keV• <β> = 12 m

• Undulator• λu = 39 mm

• Nper = 85• L = 3.315 m• Lbreak = 1.17 m (30 per)

- Simulated half for slippage• K ~ 2.07• λr = 1 nm

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Time-dependent, nonlinear harmonics

Psat ~ 2.8 GW

FWHM ~ 0.68 eV

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Time-dependent, nonlinear harmonics

Psat ~ 39 MW

FWHM ~ 1.76 eV

Relative spectral bandwidth is roughly constant5.4e-4 vs 4.7e-4

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Harmonic lasing, phase shift of 2π/3 (λ/3), steady-state

Phase shifters kill the fundamental

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Harmonic lasing, time-dependent

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Beamline geometry – 1 break

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Beamline geometry – 2 breaks

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Beamline geometry – 3 breaks

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Harmonic lasing – 3rd harmonic

P ~ 342 MW FWHM ~ 0.99 eV

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Spectral comparison at saturation points