Areas of interest Mid-IR FELs Mid-IR FELs THz FELs THz FELs phase-matched HHG for the generation of attosecond range X-ray (100 eV-multiple keVs) pulses with high average brightness FEL schemes to realize (low jitter, multi-color) pump-probe experiments mid-IR Enhancement Cavity to boost up pulse energies Photonic crystal mirrors with tunable reflectivity for high power THz FELs (broad band outcouplers with nearly 100% efficiency) realization of THz pulse stacker cavity tunable Filters and Modulators for intracavity applications

Generation of coherent X-Ray pulses by HHG (A.Foehlisch///Murnane&Kapteyn): FELs as drivers for HHG based coherent X-Ray sources ? 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 1-5x1014 W/cm2 , noble gas filled hollow waveguide apertures: ~100mm-200mm, (He) gas pressure: tens of atm) 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 ~9 mJ at 20Hz

HHG - Predictions & Measurements Popmintchev et al., PNAS 106, 10516 (2009) Curves normalized to phase-matched HHG @ λ0=0.8µm @ l= 6µm, 10 MHz rep. rate (He) estimated Photon flux : ~1013-14 ph/sec (1.0%BW) @ l= 3.9µm, 1 kHz rep. rate (35 atm. He) Photon flux : ~108 ph/sec (1.0%BW) (based on experiments) Phase matched HHG @3.9mm, 6cycle, 20 Hz Popmintchev et al., OSA/ CLEO 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 mm-7mm) (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)

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 (single spike, high gain superradiant FEL osc.) Generation of short electron pulses (JLab)

Suggested (3-6mm) MIR FEL & Pulse Stacker Cavities stretcher compressor PLE dielectric mirror NIR/MIR FELO mode matching telescope I.) II.) 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 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 !

FSU-NHMFL NIR/MIR/FIR (&broadband THz) FEL Proposal E ~ 60 MeV (NIR/MIR) E ~ 13 MeV (FIR) 135 pC pulses sz ~ 0.5 – 4 ps 10.7 MHz (21.4 MHz FIR) 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

system parameters JLab IR FEL BERLinPro (not uptodate) Beam parameters FEL (1.6mm) Units Beam Energy 115 MeV Bunch charge 110 (135) pC s_z rms 150 fs Peak current ~300 A s_e rms (uncorrelated) 0.1% (correlated) 0.5% nor. trans. Emit. 8 mrad rep. rate ~75 MHz Trim Quads reading Coherent OTR interferometer autocorrelation scans for bunch length measurements

Enhancement Cavity @ JLab Brewster W. vacuum vessel Opt. Switch mount Folded cavity FEL Input Coupler High Reflector 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)

FEL Osc. sensitivity to temporal jitter Dt/t = dL/L + df/f e- bunch 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.

FEL Osc. sensitivity to temporal jitter Jitter 5 fs rms Jitter 10 fs rms w/o initial Jitter A case study / simulations Peak power fluctuations ~4-5% rms Pulse width fluctuations limited to a few % timing jitter ~ ±20 fs (optical pulse)

Layout of a 30-100 MeV ERL Beamline Beam Dump Extractor LINAC Module II LINAC Module I Merger Injector Cavity Egun Arc I Arc II Straight Section I FEL I FEL II DBA Pump-probe NIR-MIR-FIR/THz combinations (Coherent (broadband) THz generation) (CBS X-Ray source)

Pump-Probe NIR-MIR-FIR/THz combinations