Key Points from each presentation at the MagLab Free Electron Laser workshop Held in Gainesville, FL October 27, 2005

1. Key Points from each presentation at the MagLab Free Electron Laser workshop Held in Gainesville, FL October 27, 2005 -John Singleton, chief scribe

2. The JLab IR Demo FEL and Its LegacyGeorge R. Neil and the Jefferson Lab Team • The JLab IR Demo established power records for FELs and tunable lasers by producing > 1 kW of average power in the 3 to 6 micron region. • Cryomodule- allows high power compared to copper accelerator (continuous stream of micropulses @ 75 MHz, 37.5 MHz, 18.75 MHz). Pumped Liquid Helium required (no problem with Hybrid experience). • Energy-Recovering Linac (ERL); recovers beam energy, greatly saving on RF energy. Beam dump non-radioactive. But tunability not so convenient. If TLH system can live with lower powers (factor 5), may be more convenient with no ERL. • Pulse FT limited: detuning- play off pulse length (time) versus pulse width (wavelength). • New machine: broad-band THz- versatile, high-intensity source for FTIR and pump-probe. • Can we use Compton to get time-resolved X-ray in the long term? desiderata: Thermionic versus Laser Supported by: U.S. Department of Energy - Contract DE-AC02-98CH10886 U.S. Department of Defense - ONR, AFOSR and ARO-NVESD Southeastern Universities Research Association - SURA

3. The UCSB Electrostatic-Accelerator FEL as a Prototype for NHFML G. Ramian, UCSB • With recirculation, accelerator can sustain currents ~ 2 amps for ~10s of microseconds. • Low photon energies: convenient for wavelengths 2.3 mm-63 microns (2 wigglers working well in present 6 MV machine); NHMFL machine could be run at lower voltages. • Time structure very long (microsecond) pulses. • FEL oscillator starts stochastically: many modes within gain bandwidth- need for injection locking. • Suitable for specialized applications, e.g. pulsed EPR?

4. Issues at a University Based FEL Center • T. Smith • Stanford Picosecond Free Electron Laser Center • W.W. Hansen Experimental Physics Laboratory • Stanford University, Stanford, CA 94305-4085 • The Center’s goal is to produce the best possible science. Other issues are guided by this principle. • Cryomodule-driven non-ERL system. Two undulators, 12 m cavities- MIR (3-12 microns, 0.7-3 ps), FIR (15-100 microns, 2-10 ps). Thermionic cathodes- no disadvantage wrt to laser bunch gen. • Good tunability - 4-5 different, stable wavelengths per hour • Center infrastructure: synchronised lasers, FTIR, OPAs • Two-user capability- either two undulators simultaneously or beam switching with two wavelengths/time structures of pulses. • User support system similar to NHMFL (involved scientist)

5. Regenerative Amplifier FELDinh Nguyen (LANL) • The Regenerative Amplifier FEL (RAFEL) is a high-gain amplifier with feedback driven by a compact, room-temperature RF linac. Can be moved on semi truck. • The Advanced/RAFEL facility operated from 1993 to 1999 in the spectral range 3.8 and 20 microns. Presently inactive, it requires minor modifications to be suitable for applications at the NHMFL. • The RAFEL has achieved the following performance specifications: • Wavelength range: 3.8 – 20 microns ( wiggler period = 1 – 2 cm). Could be extended to 30 microns • Micropulse energy: 2 mJ (in 15 ps micropulse) • Micropulses (1-15 ps) separated by 9 ns. • Macropulse energy: 2 J (in 20 microsecond macropulse) • Bandwidth: 6% in free running mode; expected to be narrower with the use of a pair of gratings in the feedback loop. • Modifications required for spectral purity- cylindrical grating in cavity. • The RAFEL allows early users’ experiments at NHMFL • Enable users’ experiments at NHMFL while designing the final FEL • Provide both IR and THz beams simultaneously

6. L van der Meer, FELIX • FELIX: Copper accelerator: no recycling. Two wigglers- 250 microns to 5 microns coverage. Rapid tuning (e.g. scans from 5-20 microns). • 100 ms macropulse spacing, 10 microsecond macropulse length. • Micropulses 0.3-5 ps, rep. period 1 ns to 40 ns. • 9 user stations: ancilliary equipment: synchronised lasers, OPAs, pump-probe, FTICR. • Both high brightness (e.g semiconductor spectroscopy) and high fluence (molecular beams) experiments. • FELICE- intracavity experiments (3-100 microns, several mJ). • Narrow bandwidth radiation from linac-driven FEL: continuous tunability is possible but a complex issue.

7. 4GLS - the UK’s fourth generation light source project W Flavell • 4GLS combines superconducting ERL, SR and FEL technology in a fully integrated multi-source facility covering THz - soft X-ray • The 4GLS prototype, ERLP, will be Europe’s most intense broadband THz source and will be operational from summer 2006 • The science planned in the THz/IR includes • THz spectroscopy and imaging of biological material • Studies of molecular IVR via pump-probe • Studies of the evolution of excitons in nanoparticulate systems • Coherent manipulation of semiconductor qubits • Use of THz to start surface reactions (various probes) • Very wide range of combined NIR/ MIR and THz pump-probe applications: chemistry, semiconductors, nanophysics

8. Science at the JLab FEL Gwyn P. Williams and the Jefferson Lab team. • JLab operates a 75MHz, 1-10 micron, 120 microjoule/pulse, sub-ps FEL, and also a 100W broadband THz line. • User science programs take advantage of tunability, ultrafast pulses, & high repetition rate. 100 microJ per pulse, 75 MHz. • High rep rate gives very good statistics for vibrational mode and impurity spectroscopy. Also useful in catalysis. • Bio/nano applications demand high resolution and tunability in NIR. Some bio experiments demand rapid tuning as sample reacts to incident photons. • Large FEL monochromatic power needed for low cross-section experiments (gas phase experiments). • Burgeoning number of applications (bio, nano, magnetic) for broadband THz

9. Ultrafast Time-resolved Spectroscopy of Semiconductors in High FieldsDavid Reitze, UF Physics • High Field Semiconductor ‘Quantum Optics’ • Fundamental light-matter interactions in semiconductors • Probe of semiconductor analogs of atomic systems ‘Exotic’ quantum optical phenomena • Spin Physics • Novel spintronic materials, DMS systems • Time-resolved MOKE • Quantum Control of Carrier, Spin Dynamics in High Magnetic Fields • Ultrafast shaped pulse interactions with semiconductors Controlling decoherence using strong magnetic fields • Manipulate electronic states via fluence, wavelength, field • Higher fields in combination with MIR-NIR for CR, excitons. • 1 micron to 1000 micron, 1 ps pulse, rep rate 10-30 MHz, quasi-CW operation, Power 100 W, pulse-pulse fluctuations 0.5 %, Polarization linear, circular, user friendly (novel magnets).

10. Wish List for IR FEL Source (Reitze) • Spectral Range: 1 mm – 1 mm (10-3 eV – 1 eV) • Spectral filtering before sample • Pulse Duration: 1 ps or shorter • Repetition rate: 10 – 30 MHz • Quasi-CW operation • Beam quality: • Diffraction-limited focusing at all wavelengths • Power: • Average output power > 100 W (with attenuation capability!) • Pulse-pulse fluctuations: < 0.5% rms • Polarization: linear, circular • Synchronization: Electronic synchronization with lasers, lock-ins, etc… • Up-time • User Friendliness • Magnet/beam interface (optics, positioning) • Faraday, Voigt geometries

11. Optically-pumped Magnetic Resonance at High-Fields, J Singleton, LANL • Very important to have widely tunable pump energy (MIR, FIR) followed by time-delayed broad-band THz pulse plus high magnetic fields (45 T). • Enables Optically-Pumped Magnetic Resonance (OPMR), where “magnetic resonance” includes Cyclotron Resonance (CR) and Electron Paramagnetic Resonance (EPR). • OPMR explicitly probes magnetically-split excited states, even optically-dark states, giving their energy structure and time dependence. • Wide range of adjustable parameters- pump wavelength, pump intensity, field (splits excited state and tunes groundstate), probe time delay, probe intensity. • OPMR can probably be used in quite a general way to look at ps time dependence of carrier transient populations, optically/heat initiated chemical reactions, biological reactions

12. Terahertz magneto-optics in semiconductors with the UCSB FELs: Rabi oscillation of impurity-bound electrons M. S. Sherwin, UCSB 1: Pulse slicing Pulse duration variable from fractions of a ns to a few s 2: Rabi oscillations of impurity-bound electrons Frequency ~ 1.5 THz, times ~10s to 100s of ns. 3: Optical readout of impurity state Resonant elastic light scattering 4: Lifetime measurements Preliminary measurements of population relaxation times (T1 ?) Plans for photon echo (T2) Experimental issues New opportunities

13. Infrared magneto-optics of correlated electron matter D.N. Basov University of California, San Diego 1: High-Tc superconductors vortex state “floating phases” inhomogeneous condensate 2: Electrostatic doping of materials and FET structures An IR probe of charge injection 2D electron gas in organic and inorganic FETs graphene and graphite Bright sources and time resolution important Go as far as MIR 3: Heavy electron fluids quantum criticality: hybridization gap, optical mass, very low reflectivity. FEL @ NHMFL Experimental issues New opportunities

14. FEL@NHMFL and Correlated Electron Matter D.Basov, UCSD • Instrumental requirements: • broad w range spectroscopy: sub-THz – mid-IR • high stability of intensity; • R(w) uncertainty 0.1-0.3 % T(w) uncertainty 0.01 % • 0.3 K – 300 K • Micro-sample capabilities 10mm • Faraday and Voigt • Polarization analysis • Circular polarization? • Spectroscopic ellipsometry? • Pump-probe experiments ?

15. Time domain EMR with a FELJ van Tol – LC Brunel • Time domain coherent excitation of magnetic dipole (spin) transitions in the 200-1500 GHz (1.5 – 0.20 mm) frequency range. • High frequency gives better resolution and entanglement. • For fast measurements (short T2 systems) the power should be ~1 kW for a 500 ps-1 ns pulse. Q = 1000 cavity. • Applications: quantum information, spintronics, coupled spin systems, distance measurements in biology. • From discussion- can we do the same thing (i.e. construct a nanosecond pi or pi/2 “pulse” using a train of closely-spaced coherent micropulses)? There are good precedents in NMR. Adjacent pulses are known to be coherent (FELIX, Stanford). • Detection scheme?

16. High-field/frequency EMR: Applications to molecularconductors,superconductorsandmagnets Stephen Hill, University of Florida, Physics • Cyclotron resonance and related • Probe electronic structure of novel conductors/superconductors • Split-gap magnet/ flexible geometry needed for angle-dependent effects. • High frequencies, high fields, extend CR to cuprates and other dirty things • Field-induced phenomena (phase transitions induced by field): pulsed fields? • Quantum dynamics of magnetic nanostructures • High-frequency (large zero-field splittings ~300 GHz), high field (> 10 T) pulsed EPR • Coherent quantum control • Control of singlet/triplet populations by high fields • GHz/THz spectroscopy • Summary of what is needed: 10s GHz to 1 THz

17. Precision spin manipulation with ESR A Ardavan, Oxford • * A high-power pulsed infrared source makes us think straight away of • doing pulsed magnetic resonance. • * Using the FEL, we can get component pulses of complex sequences using • one of two basic approaches: •         (1) beam-split a single pulse, or •         (2) use successive FEL pulses. • * Which is better depends critically on whether we can ensure phase • coherence between pulses, and how good the phase coherence is. • * There are various strategies that one can adopt to measure the quality • of and the nature of the errors in the pulses using sequences like • CP/CPMG and SPAM. These might provide a useful tool for characterizing • the inter-pulse phase coherence of the FEL. • Pulse-pulse coherence? • Multiplexer? • Errors in A?Errors in? • Systematic or random errors? • Detection scheme? • Learn from conventional EPR techniques: FEL ENDOR etc.

18. Applications of Free-Electron Laser Based Instrumentation in Optical Microscopy and Cell Biology Michael W. Davidson, Optical Microscopy, NHMFL • Infrared Tissue Ablation (Vanderbilt FEL ~ 5-7 mm) • Laser Microsurgery (Ophthalmology and Neurosurgery) • Infrared Near-Field Scanning Optical Microscopy • Time-Resolved Spectroscopy (Pulsed IR and UV Lasers) • Coherent Imaging of Biomolecules, Viruses and Bacteria • Need some zero-field user stations? • Or is this better served at some other FEL? • Might the requirements of a zero-field tail wag the “FEL for high field experiments” dog (or dawg)? • G. S. Edwards, et al, Photochem. Photobiol. 81: 711 (2005) • G. S. Edwards, et al, Rev. Sci. Instr. 74: 3207 (2003) • S. Krishnagopal, et al, Current Science 87: 1066 (2004) • D. Vobornik, et al, Infrared Phys. Technol. 45: 409 (2004) • SNOM

19. Magneto-Dynamics with an Accelerator-Based THz Source G. Lawrence Carr National Synchrotron Light Source / Brookhaven National Laboratory (carr@bnl.gov) • THz magneto-spectroscopy with incoherent synchrotron radiation. • Source qualities, program overview (AF resonance, multi-ferroics) • Magnetospectroscopy of superconductors • Quasiparticle dynamics in the mixed state • Linac-based coherent THz pulses • Pulse characteristics (100 microJoule, 840 pC, 10 Hz, 0-2 THz, 1/2 or single-cycle pulses, 300 fs, 1 MV/cm, 3 kG) and detection • Potential for studying transient high-field effects in materials • Pulse can be pump and probe

20. Ultrafast Structural Probe Using Near-Relativistic Electron Bunch. Jim Cao, FSU / NHMFL • Use the sub-ps electron bunch in FEL to do ultrafast diffraction. • Potential to do real single shot measurement of laser-induced ultrafast structural dynamics in solids. • Increases the diffraction signal up to several orders of magnitude while maintaining the ps to sub-ps time resolution. • Melting. • Phonon generation. • Jahn-Teller distortion. • Dynamics of chemical reactions. • Better to use separate 5 MeV accelerator with high beam quality?

21. Infrared Spectra of Gaseous IonsJohn R. Eyler • Infrared Multiple-Photon Dissociation Spectra Obtained in Ion Trapping Mass Spectrometers • Many Successful Experiments Carried Out using NHMFL-Supported FTICR Mass Spectrometer at FELIX in Recent Years • Desired Operating Parameters • Output Range - ~250 – 3600 cm-1 (~ 2.8 – 40 μm) • Output Power - > 500 mW, 50-100 mJ per macropulse (collection of pulses), • more would be good • Constant stream of micropulses good (variable length of irradiation needed = simulated macropulse of widely variable length) • Also Important • Facile Tunability Over Wide Wavelength Range • Experimenter Control Over Wavelength Range, Steps • Travel to Tallahassee would be easier!

22. Application of FELs in Structural Biology N L Greenbaum, FSU 1- Biological processes in the THz frequency range: important information about hydrogen bonding: 0.1 to 10 THz desirable. Intense broadband source, high rep. rate (37 MHz)- good for thick samples. Time dependence and dynamics on nanosecond timescale. 2- Use of FELs for IR Absorption spectroscopy: spectroscopy with high sensitivity in MIR. 3- FELs and Magnetic Resonance (GHz-low THz range): pulsed EPR. Timescales of e.g. photosynthesis 3 ps to 200 microseconds. Pump-probe: probe EPR @ 36 T coupled with FEL pulse pump. 4- ENDOR type experiments (FEL as light source). 5- Circular dichroism/polarization.

23. 1 G. Neil 2 G. Ramian 3 T. Smith 4 D. Nguyen 5 L van der Meer 6 W Flavell 7 G Williams 8 D Reitze 9 J Singleton 10 M Sherwin 11 D Basov 12 LC Brunel 13 S. Hill 14 A Ardavan 15 M Davidson 16 L Carr 17 J Cao 18 J Eyler 19 N Greenbaum Session chairs: T Smith, S. Hill, J Singleton, LC Brunel

24. NHMFL – Free Electron Laser - Project Management NHMFL-FEL Management Oversight Greg Boebinger, NHMFL NHMFL External Advisory Committee NHMFL Executive Committee FEL Business Manager Brian Fairhurst, NHMFL NHMFL Users’ Committee NHMFL-FEL Project Manager Hans Van Tol, NHMFL Chief Budget Officer Terrie Price, NHMFL JLab/UCSB FEL Design Team George Neil, Jefferson Lab FEL Design Integration with NHMFL Facility Bruce Brandt, NHMFL FEL Design Integration with Scientific Vision John Singleton, NHMFL NHMFL User Program Scott Hannahs, NHMFL Condensed Matter Physics John Singleton, NHMFL JLab Experimental Prototype Lab John Singleton, NHMFL Chemistry Nancy Greenbaum, FSU NHMFL Magnets John Miller, NHMFL Electron Magnetic Resonance Louis-Claude Brunel, NHMFL UCSB Experimental Prototype Lab Louis-Claude Brunel, NHMFL Biophysics Krastan Blagoev, LANL Rafael Bruschweiler, FSU NHMFL Site Plan John Kynoch, NHMFL FEL Advisory Council Mark Sherwin, UCSB Todd Smith, Stanford Lex van der Meer, FELIX Scientific Advisory Council Walter Pidgeon, Edinburgh Dave Piston, Vanderbilt Dave Reitze, U Florida Gwyn Williams, JLab Jim Allen, UCSB Dmitri Basov, UCSD Jun Kono, Rice Joe Orenstein, UC Berkeley

25. How can the RAFEL be used at NHMFL?D Nguyen, LANL • Demonstrate proof-of-principle experiments at Los Alamos High Magnetic Field Laboratory (in collaboration with John Singleton) • Probe dynamics with picosecond IR pulses up to the 20-ms time scale. • Perform picosecond pump-probe experiment (FEL provides IR pump) • Perform THz spectroscopy (FEL provides tunable THz pulses) • Reduce risks • Gain run-time experience while designing the final FEL • Explore FEL operational characteristics that are suitable for NHMFL • Improve final FEL design with users’ feedback

26. Some rough requirements of the facility (Hill) • Frequency range (ideally variable/tunable) • Tens of GHz to > 1 THz (1.7 cm-1- 33 cm-1, 0.2 meV - 4 meV) • High fields (even pulsed) and magnets with variable geometries • Power (coupled to cavity/sample) • 50 mW for 100 ns pulse - may be achievable with existing sources • 100+ W for 1 ns pulses • Timing (coherent if multiple pulses are utilized) • Depends on T1 and T2 • Current optimistic lower bounds on T2 on the order of 50 ns • Therefore, 1 nanosecond up to 100 ns (or even 1 microsecond) • Variable timing (may require additional switches) • Dead times of nanoseconds to milliseconds (maybe even seconds!) hf = gmBB; 10-50 T ~ 300 – 1500 GHz