1

SummarySummary

Maximum Intensity Maximum desired beam current is 10 nC/pulse. Minumum photocathode QE before replacement is .5%. This requires 9.4 µJ/pulse at the photocathode.

Maximum pulse length 4 stacked gaussian pulses, each with RMS = 2.3 psec (FWHM = 5.4 psec), separated by 2.3 psec yields a pulse with RMS = 6.3 psec (FWHM = 20.8 psec). Intensity variation at flattop is <±5%.

Minimum pulse length RMS = 2.3 psec (FWHM = 5.4 psec). This is the minimum the laser system can deliver.

Maximum spot size Photocathode is 5 mm in diameter, so maximum spot size is 5 mm FW of any shape.

Minimum spot size RMS = 1.0 mm (FW = 4.0 mm) "flat" transverse profile @ 3.2 nC/pulse, 4 stacked gaussians; RMS = ?? mm "flat" transverse profile, @ ?? nC/pulse

Maximum pulse train 3000 pulses @ 5 Hz

Minimum pulse train 1 pulse @ 1 Hz

Pulse-to-pulse intensity fluctuation ??% RMS

Notes -- Generation of laser pulses with a flattened transverse profile requires the use of an iris, which diminishes intensity. -- Stacking 4 gaussian pulses is ~70-80% efficient. (J. Ruan) -- Transport efficiency from uv target to photocathode is 10-20% (J. Ruan) -- Trade offs are between intensity, transverse emittance, momentum spread, and bunch length

2

Stacked GaussiansStacked Gaussians

0.0000000

0.0500000

0.1000000

0.1500000

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t [ps]

0.0000000

0.0500000

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0.3500000

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t [ps]

4 gaussians @ σ=2.3 ps; separation=2.3 ps

FWHM=20.8 ps; RMS=6.4 ps

4 gaussians @ σ=2.3 ps; separation =1.4 ps

FWHM=13.0 ps; RMS=4.3 ps

with spot size = 1.2mm RMS (flat distribution, 4.8mm dia.) and 3.2 nC/pulse yields 3.5E-6 emittance, dp/p (FW) = ±3.2%, and RMS bunch length = 320 µm after bunch compression (no 3rd harmonic cavity)

3

Irised GaussianIrised Gaussian

σ = 2.85mm; iris = 4.8mm dia

intensity reduced to 30%; phase space density variation of ±17.5%

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x [mm]

irised gaussian

flat distribution

gaussian