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Generation of Ultrafast Mid-IR pulses using a 100 MeV ERL-FEL (Drivers for tunable HHG based coherent X-Ray sources ?). Phase matched HHG using mid-IR lasers (Experiments). T. Popmintchev, nature photonics | VOL 4 | DECEMBER 2010. Generation of coherent X-Ray pulses by HHG.

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slide1

Generation of Ultrafast Mid-IR pulses using a 100 MeV ERL-FEL

(Drivers for tunable HHG based coherent X-Ray sources ?)

slide2

Phase matched HHG using mid-IR lasers (Experiments)

T. Popmintchev, nature photonics| VOL 4 | DECEMBER 2010

Generation of coherent X-Ray pulses by HHG

  • Idea (A.Foehlisch): Can we drive HHG by a compact ERL(FEL)?
  • requirements imposed on drive lasers :

- HHG (phase matched) needs preferably few cycle to ~10 cycle drive laser pulses in NIR/MIR and intensities in the range of 1-5x1014 W/cm2(noble gas filled hollow waveguide apertures: ~100mm-200mm )

  • OPCPA’s
  • NIR sub-10 fs with 70 mJ energy at 100kHz.
  • NIR sub-10 fs multi-kHz, multi-mJ
  • Mid-IR (~3mm) sub-100 fs with a few micro-Joule energy at 100kHz
  • 3.9 mm sub-100 fs with 6 mJ at 10-20Hz
slide3

Outline :

  • short term: carrying out the HHG experiments on an existing FEL facility that meets the requirements set on the mid-IR drive laser, verifying the theory throughout the mid-IR (and beyond 10 mm if necessary) (JLab ???)
  • long term: mid-IR ERL-FELs should be able to perform better than atomic lasers in terms of :
  • tunability (throughout the nir/mid IR and beyond)
  • rep rate (MHz) in generating mJ(s) of ultrafast pulses with high average power (problems in CEP stabilization???)
  • simulation study has been and still is mainlyfocused on the latter and on the question:
  • What system requirements will be imposed on a compact ERL, (particularly concerning timing jitter budget)
slide4

Ultrashort Pulse Generation in (Mid IR) FELs

  • Chirped pulse generation in a FEL oscillator using a chirped electron beam and pulse compression (JLab)
  • Mode-locking techniques in FELs
  • -Active mode-locking (multiple OK sections used in a
  • cavity)
  • - Passive mode-locking (JAERI, lasing at l~22 mm)
  • (single spike, high gain superradiant FEL osc.)
  • Generation of short electron pulses (JLab)
slide5

E ~ 60 MeV (NIR/MIR)

E ~ 13 MeV (FIR)

135 pC pulses

sz ~ 0.5 – 4 ps

10.7 MHz (21.4 MHz FIR)

FSU-NHMFL NIR/MIR/FIR (&broadband THz) FEL Proposal

X

FIR

NIR

inclusion of a HHG based coherent X-Ray source ?

MIR/FIR

Parameter NIR FEL MIR FEL FIR FEL

Wavelength (μm) 2.5 to 27 8 to >150 100 to 1100

Wawenum (cm−1) 400 to 4000 < 70 to 1300 9 to 100

slide6

Trim Quads reading

system parameters

JLab IR FEL

BERLinPro

Coherent OTR interferometer autocorrelation

scans for bunch length measurements

slide7

compressor

stretcher

mode matching telescope

PLE

dielectric mirror

NIR/MIR FELO

Suggested (3-6mm) MIR FEL & Pulse Stacker Cavity

  • - Beam Energy: 100 MeV
  • - Bunch Charge: 80 pC
  • - Rep rate: 40 MHz
  • - Outcpl.Pls. Energy: 50-70mJ
  • -Cav. Enhancement: 80-100
  • Pulse width: ~100-200fs (fwhm)
  • IL~ 1x1014 – 3.5x1014W/cm2

Mode-locked

NIR Laser

  • high-Q enhancement cavity (EC) smoothes out power and timing jitter of the injected pulses inherent to FEL interaction.
  • allows fs (10 -100 ?) level synchronization of the cavity dumped mid-IR pulse with the mode-locked switch laser.

- Depending on the recombination time of the fast switch, sequence of micropulses with several ns separation can be ejected from the EC !

slide8

Folded cavity

vacuum vessel

Input Coupler

FEL

Opt. Switch mount

High Reflector

Brewster W.

Enhancement Cavity @ JLab

Q ~ 40 (Finesse ~ 300 ) enhancement :~90

Q~ 50

enhancement :~130-140

estimated enhancement @ JLab ~ 100

T. Smith @ Stanford IR-FEL achieved enhancement of ~70 - 80 using an external pls stacker cavity (1996)

slide9

3 mm- 6 mm Short Pulse FEL (cavity detuning)

~ 3 mm

100fs (fwhm)

Dw/w~ 4%-5%

  • low time jitter
  • low peak to peak power deviations
  • Outcoupled Pulse Enegies: ~ 50-70 mJ
  • ~ 10 cycle pulses
  • (HHG drive laser)

~ 6 mm

Dw/w~ 4%-5%

200fs (fwhm)

Talk in Nov. 2010

slide10

High Gain (superradiant) FEL Oscillator operating at cavity synchronization

35 - 40fs (fwhm)

Synchrotron Osc. Freq.

lc ~ 45fs

  • nearly an order of magnitude higher outcoupled pulse intensity (despite low outcoupling ratios)
  • FEL efficiency in superradiance mode more than doubled

Talk in Nov. 2010

slide11

3D (semi-)frequency domain

1½D - SVEA time domain

Comparison between two FEL simulation methods

(superradiant) FEL [email protected] synchr.\' case

‘FEL oscillator-cav. detuning\' case

  • good agreement between the models in \'FEL oscillator with cavity detuning\' case
  • (in terms of outcoupled pulse energy, temporal and spectral pulse profiles)
  • Disagreements in the \'superradiant operation at cavity synchronism\' in obtaining self similar pulses following saturation, differences in temporal and spectral pulse profiles.
slide12

e- bunch

Dt/t = dL/L + df/f

FEL Osc. sensitivity to temporal jitter

  • Dt: timing jitter
  • L : cavity length
  • dL: cavity length detuning
  • f : bunch rep. frequency (perfectly synchronized to L)
  • : cavity roundtrip time ( 2L/c)
  • Bunch time arrival variation effectively has the same effect
  • as cavity length detuning.
  • effect of the timing jitter on the FEL performance
  • In slippage dominated short pulse FEL oscillators cavity detuning is necessary to optimize the temporal overlap between optical and e- pulses (Lethargy effect).Timing jitter induces fluctuations on the operational cavity detuning.
slide13

w/o initial Jitter

Jitter 5 fs rms

Jitter 10 fs rms

FEL Osc. sensitivity to temporal jitter

~ 6 mm

~ 6 mm

Simulation using BERLinPro parameters, \'FEL oscillator with cavity detuning\'

  • Peak power fluctuations ~4-5% rms
  • Pulse width fluctuations limited to a few %
  • timing jitter ~ ±20 fs (optical pulse)
slide14

DP~2% rms

100fs (fwhm)

FEL Osc. sensitivity to temporal jitter

l~ 3 mm

Simulation using BERLinPro parameters, \'FEL oscillator with cavity detuning\'

w/o initial jitter

jitter 5 fs rms

  • Peak power fluctuations ~8 -10% rms
  • Pulse width fluctuations limited to a few % rms
  • Timing jitter ~ ±20 fs (optical pulse)
slide15

Timing jitter measurements @ JLab IR-FEL

(P. Evtushenko , ELECTRON BEAM TIMING JITTER AND ENERGY MODULATION MEASUREMENTS AT THE JLAB ERL )

(Beam Current Monitor (cavities) and Signal Source Analyzer employed for power spectrum measurements at harmonics to characterize phase noise)

  • phase noise spectra measured in the vicinity of the wiggler-entrance (behind the bunch compressor)
  • e- bunch length: 150 fs rms
  • average current : 0.5 mA to 4.5 mA (bunch charge ~135 pC kept constant, bunch rep rate varied)
  • measured timing jitter :
  • ~25 fs rms @ 1.5 mA - ~80 fs rms @ 4.5 mA
  • estimated FEL spec (to keep pp-power fluct. below 10 % @ l = 1.6 mm ) on arrival time jitter : dL/L < 3.8x10-8
slide16

jitter 2.5 fs rms

jitter 2.5 fs rms

FEL Osc. sensitivity to temporal jitter

~ 6 mm

1D-SVEA Simulation using BERLinPro parameters, \'superradiant operation at cavity synchronism\'

jitter 2.5 fs rms

w/o initial jitter

jitter 2.5 fs rms

slide17

~5sE

DN/N

~5sE

Dg/gr

DN/N

Dg/gr

Calculated spent beam energy distribution @FEL saturation

  • 8% -10% spent beam momentum spread (full)generated by the FEL interaction
  • large energy spread acceptance is required for beam transport/energy recovery
  • (JLab IR Upgrade acceptance :~15 %)

l=3 mm

l=6 mm

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