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

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

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  1. Generation of Ultrafast Mid-IR pulses using a 100 MeV ERL-FEL (Drivers for tunable HHG based coherent X-Ray sources ?)

  2. 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

  3. 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)

  4. 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)

  5. 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

  6. Trim Quads reading system parameters JLab IR FEL BERLinPro Coherent OTR interferometer autocorrelation scans for bunch length measurements

  7. 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 !

  8. 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)

  9. 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

  10. 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

  11. 3D (semi-)frequency domain 1½D - SVEA time domain Comparison between two FEL simulation methods (superradiant) FEL Oscillator@ 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.

  12. 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.

  13. 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)

  14. 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)

  15. 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

  16. 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

  17. ~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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