Compact ERL-FEL/Pulse Stacker Cavity configurations: new high rep rate, high intensity driver sources for High Field Applications ? Mufit Tecimer THz-FEL Group, University of Hawai’i at Manoa KEK, Tsukuba, Japan April 20, 2012

The rationale of the presented study is an old idea regarding electron beam based radiation sources:  To tap on the (high) power deposited in the electron beam by elaborating on schemes with high extraction efficiency,  Use of the generated radiation in Applications relevant to the current research/ technological development.

High Field Applications I.) Upfrequency conversion in the x-ray region phase-matched High order Harmonic Generation (HHG) attosecond science x-ray Parametric Amplification (XPA) II.) Laser driven plasma-based electron accelerators Laser Wake Field Accelerator (LWFA) III.) Inverse Compton Scattering (ICS).....

Generation of coherent X-Ray pulses by HHG Three-Step Model (Corkum 1993) Popmintchev et al., OSA/ CLEO 2011 (single atom HHG)

requirements imposed on drive lasers (Popmintchev et al.) : Phase-matched HHG in keV region photons needs:  preferably few cycle (CEP stabilized) to ~10 cycle drive laser pulses in NIR/MIR,  intensities in the range of 1-5x10 14 W/cm 2,  noble gas filled hollow waveguide apertures: ~100m-200m, (He) gas pressure: tens of atm) Generation of coherent X-Ray pulses by HHG OPCPA’s NIR sub-10 fs with 70 mJ energy at 100kHz. NIR sub-10 fs multi-kHz, multi-mJ Mid-IR (~3  m) sub-100 fs with a few micro-Joule energy at 100kHz 3.9  m sub-100 fs with ~9 mJ at 20Hz The idea of using Mid-IR (ERL) FELs as drivers for HHG thought of or considered by Kapteyn /Murnane (JILA), Foehlisch (Bessy) and others …

Popmintchev et al., PNAS 106, (2009) Curves normalized to phase-matched λ 0 = 6µm, 10 MHz rep. rate (He) estimated Photon flux : ~ ph/sec = 3.9µm, 1 kHz rep. rate ( atm. He) Photon flux : ~10 8 ph/sec (1.0%BW) (based on experiments) Popmintchev et al., OSA/ CLEO 2011 Phase matched  m, 6cycle, 20 Hz HHG - Predictions & Measurements (single atom HHG) M. Tecimer, FHI-Berlin (FEL Seminar), Sep. 29, 2011

HHG - Predictions & Measurements to be published by Kapteyn/Murnane Group (JILA) in Science He driven by 20 μm mid-IR lasers may generate bright 25 keV beams. [Ref.: Kapteyn/Murnane, Quantum Physics and Nonlinear Optics at High Energy Densities]

XPA Experiments synchronized FEL pulses (figure modified from H.Kapteyn, Quantum Physics and Nonlinear Optics at High Energy Densities) B. Aurand et al., NIM A 653, 130 (2011) A claimed maximum gain of about 8000 at 50eV photon energy is demonstrated. Amplified spontaneous emission Amplifier with a seed J. Seres et al., Nature Phys. 6, 455 (2010).

FEL pulse Tens of TWatts few optical cycles synchronized FEL pulses Reference: C.B. Schroeder, E. Esarey, C.G.R. Geddes, C. Benedetti, and W.P. Leemans, Phys. Rev. ST Accel. Beams 13, (2010). e - beam GeV multiple stages " Modified " Cascaded/Staged LWFA using FEL d r iver pulses J. S. Liu et al., PRL 107, (2011) (Figure modified from 'High Power Laser Technology',Wim Leemans, LBNL) Joule level driver laser ~1  m n~ cm -3 ~  m (?) electrons are repeatedly accelerated by the laser wakefields in a manner similar to the conventional accelerators... ..

Trim Quads reading Beam parameters FEL (1.6  m ) Units Beam Energy115MeV Bunch charge110 (135)pC  _ z rms 150fs Peak current~300A  _ e rms (uncorrelated) 0.1%  _ e rms (correlated) 0.5% nor. trans. Emit.8  rad rep. rate~75MHz Coherent OTR interferometer autocorrelation scans for bunch length measurements [S. Zhang et al., FEL 09 Conf. Proceedings] System parameters used in the Simulations JLab IR FEL M. Tecimer, Bessy-Berlin (Machine Group Seminar), Apr. 12, 2011

Outline of the project:  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 (particularly at around 6  m-7  m) (JLab, FHI-FEL, …?)  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) - high rep rate (MHz) in generating mJ(s) of ultrafast pulses with high average power Ongoing simulation work is mainly focused on the latter : (system requirements imposed on a compact ERL) M. Tecimer, Bessy-Berlin (Machine Group Seminar), Apr. 12, 2011

stretcher compressor PLE dielectric mirror NIR/MIR FELO mode matching telescope  high-Q enhancement cavity (EC) smoothes out power and timing jitter of the injected pulses inherent to FEL interaction.  allows ~fs level synchronization of the cavity dumped mid-IR pulse with the mode-locked switch laser. Mode-locked NIR Laser  Depending on the recombination time of the fast switch, sequence of micropulses with several ns separation can be ejected from the EC ! Suggested (3-6  m) MIR FEL & Pulse Stacker Cavities II.) I.) M. Tecimer, Bessy-Berlin (Machine Group Seminar), Nov.04, 2010 & Apr. 12, 2011

Brewster W. vacuum vessel Opt. Switch mount Folded cavity FEL Input Coupler High Reflector T. Stanford IR-FEL achieved enhancement of ~ using an external pls stacker cavity (1996) Q ~ 40 (Finesse ~ 300 ) enhancement :~90 Q~ 50 enhancement :~ estimated JLab ~ 100 Enhancement JLab M. Tecimer, Bessy-Berlin (Machine Group Seminar), Apr. 12, 2011

Chirped pulse generation in a FEL oscillator using a chirped electron beam and pulse compression Mode-locking techniques in FELs -Active mode-locking - Passive mode-locking Generation of short electron pulses Ultrashort (few cycles) Pulse Generation in (IR-THz) FELs M. Tecimer, Bessy-Berlin (Machine Group Seminar), Nov. 04, 2010

Passive modelocking in conventional (atomic) laser : - Kerr Lens modelocking - Semiconductor Saturable Absorber Mirrors (SESAM) - Does FEL have a self (passive) modelocking mechanism ? (for instance intensity dependent absorber) Ultrashort Pulse Generation by passive modelocking Synchrotron Osc. Freq. : M. Tecimer, Bessy-Berlin (Machine Group Seminar), Nov. 04, 2010 Nonlinear reflectivity data for a representative SESAM sample (figure added to the original) FEL oscillator with perfectly synchronized cavity (single spike, high gain superradiant FEL oscillator)

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 ~22  m) (single spike, high gain superradiant FEL osc.) Generation of short electron pulses (JLab) Ultrashort Pulse Generation in (Mid-IR) FELs M. Tecimer, Bessy-Berlin (Machine Group Seminar), Apr. 12, 2011

Further studies: - cascaded oscillator schemes (problem: large momentum spread for the beam transport/energy recovery) - use of (assistant) SESAM mirrors - checking the results with other well established codes High Gain (superradiant) FEL Oscillator operating at cavity synchronization M. Tecimer, Bessy-Berlin (Machine Group Seminar), Nov. 04, 2010

coupled FEL oscillators U(1) = U(2) (better U(1) > U(2) ) Mirror coupling ratios of are optimized I.) II.) FEL oscillators with perfectly synchronized cavity relatively large Outcoupling

U(1) = U(2) > U(3) = U(4) … U(1) > U(2) > U(3) > U(4) … Mirror coupling ratios of are optimized Amplifier stage follows the coupled FEL oscillators I.) II.) Cascaded system of coupled oscillators

Time domain multi-mode appraoch using SVEA Space-frequency representation of the electromagnetic fields and current sources Exact first order ordinary differential equations of the axial dimension without the need of introducing any approximations. Inverse Fourier Transform is necessary to construct the fields used to determine particle’s motion.

Contrasting approaches used for FEL simulation First Stage (master oscillator) a.)b.)c.) d.)e.)f.) 1D SVAE (complex field amplitude of a carrier wave) 3D non-averaged, multifrequency (multimode) code M. Tecimer, PRST-AB 15, (2012)

Simulated temporal/spectral characteristics of mid-IR pulses I.) II.) III.)

~ 5x10 -4 ~5 – 10% of optimum output pulse energy ~10 -7 feed back ~65-70% of optimum output, feed back reduced to less than to reach nearly the optimum output, limit cycle oscillations reduce strongly feedback ~5x10 -4 Beam & Optical Pulse locking Optical Pulse locking Partial bilateral Coupling of FEL Oscillators

Master Oscillator: beam longitudinal phase space a.) b.) Undulator exit

a.) Slave FEL Oscillator: beam longitudinal phase space b.) Undulator entrance Undulator exit

? Slave FEL Oscillator: beam longitudinal phase space Undulator entrance Undulator exit

 : timing jitter L : cavity length  L: cavity length detuning f : bunch rep. frequency (perfectly synchronized to L)  : cavity roundtrip time ( 2L/c)  /  =  L/L +  f/f e- bunch FEL Osc. sensitivity to temporal jitter  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. M. Tecimer, Bessy-Berlin (Machine Group Seminar), Apr. 12, 2011

FEL Osc. sensitivity to temporal jitter ~ 6 m jitter 2.5 fs rms w/o initial jitter jitter 2.5 fs rms M. Tecimer, Bessy-Berlin (Machine Group Seminar), Apr. 12, 2011

The presented coupled oscillator scheme should be applicable to longer mid-IR (THz) wavelengths by using the low loss, high reflectivity dielectric mirrors developed for THz- FEL applications. High Reflectivity Dielectric Mirrors for the mid-IR & THz regions M. Tecimer, K. Holldack and L. Elias, PRST-AB 13, (2010)

Summary MeV range superconducting ERL driven mid-IR FELs hold great promise in filling a unique niche for generating multi-mJ level (possibly much higher), ultrashort ( <10 cycles) pulses tunable within the entire mid-IR region (and beyond) with at least many tens of MHz repetition rates. Because of their ability in providing high peak intensities with excellent temporal and transversal coherence characteristics at unprecedented high repetition rates across the entire NIR/MIR spectral range, they have the potential to become attractive tools in various strong field applications alone or in combination with high finesse enhancement cavities.

References: HHG: T. Popmintchev et al., Nature Photon. 4, 822 (2010). M.-C. Chen et al., Phys. Rev. Lett. 105, (2010). G. Andriukaitis,T. Balciunas, S. Alisauskas, A. Pugzlys, A. Baltuska, T. Popmintchev, M. C. Chen, M. M. Murnane, and H. C. Kapteyn, Opt. Lett. 36, 2755 (2011). Henry Kapteyn and Margaret Murnane, Quantum Physics and Nonlinear Optics at High Energy Densities - Applications in Plasma Imaging R. J. Jones, K. D. Moll, M. J. Thorpe, and J. Ye, Phys.Rev. Lett. 94, (2005). XPA: J. Seres et al., Nature Phys. 6, 455 (2010). L. Gallman, Nature Phys. 6, 406 (2010). LWFA: J. S. Liu et al., PRL 107, (2011). Wim Leemans, LBNL,White Paper of the ICFA-ICUIL Joint Task Force – High Power Laser Technology for Accelerators. and references in M. Tecimer, PRST-AB 15, (2012)

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