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									                                  MIT X-ray Laser Project




  An X-ray Laser at the Transform Limit:
Technical Challenges and Scientific Payoff

               David E. Moncton
       Massachusetts Institute of Technology



                      NSLS
                February 20, 2004
                                                          MIT X-ray Laser Project

                      MIT X-ray Laser R&D Proposal
                             Contact: David E. Moncton, Director
                                   Telephone: 617-253-8333
                                      E-mail: dem@mit.edu
                       website: http://mitbates.mit.edu/xfel/indexpass.htm



Co-Principal Investigators                         Science Collaborators
  William S. Graves                     Simon Mochrie                Keith A. Nelson
  Franz X. Kaertner                     Gregory Petsko               Dagmar Ringe
  Richard Milner                        Henry I. Smith               Andrei Tokmakoff


 Bates Senior Staff                                      Contributors
 Manouchehr Farkhondeh                  William M. Fawley            James Fujimoto
 Jan van der Laan                       Ian McNulty                  Erich Ippen
 Christoph Tschalaer                    Jianwei Miao                 Denis B. McWhan
 Fuhua Wang                             Mark Schattenburg            Michael Pellin
 Abbi Zolfaghari                                                     Gopal K. Shenoy
 Townsend Zwart
                                  MIT X-ray Laser Project

A Unique Opportunity– An X-ray Laser User Facility
    •30 or more independent beamlines
    •Fully coherent milli-Joule pulses at kHz rates
    •Wavelength range from 200 nm to 0.1 nm

The Scientific Impact

    Femtosecond pulse duration       Chemistry

    Full transverse coherence        Biology

    Milli-volt bandwidths            Condensed Matter Physics

    Full quantum degeneracy          Atomic Physics


    High electric field              Fundamental Physics
                                               MIT X-ray Laser Project

Photon pulses would be “transform-limited” satisfying the
 Uncertainty Principle in all six phase-space dimensions


   Transverse Phase Space
     Dx , Dy ~ 100 microns
     Dkx , Dky ~ 10-5 nm-1




                         Longitudinal Phase Space
                      Dt ~ 1fs - 1ps   Dw ~ 2eV - 2meV


   Note that all 1011 to 1014 photons in each pulse would
              occupy the same quantum state
                                      MIT X-ray Laser Project

              Inelastic X-ray Scattering (IXS)
Photon-in – photon out       Probes charge-neutral excitations:
               q=ki-kf       • Phonons, diffusive modes, orbitons,
               w=wi-wf       superconducting gaps…

                             • Excitons, plasmons, particle-hole
                             creation, interband transitions…


    Complements existing techniques:
   • ARPES measures A(q,w), surface sensitive.
   • INS does not couple to charge, and requires large sample.
   • EELS cannot measure to large q, or in fields.
   • s(w), Raman are restricted to q=0.
                                  MIT X-ray Laser Project

    Existing 3rd Generation IXS Beamlines
                                       ESRF




  ESRF                 APS              Spring-8
                                       APS


•3 Beamlines with meV resolution, 2 more soon
•1 Beamline with 100 meV resolution
•2 Beamlines with eV resolution
                                MIT X-ray Laser Project

    IXS with 3rd Generation Synchrotron Sources



• Data taken on APS ID3      TiOCl
• 2.2 meV resolution
• 109 incident flux
• Data shown took 6 hrs




                              E. Isaacs, Y. Lee, D. Moncton
                                       MIT X-ray Laser Project

Large IXS Signal Gain with Bandwidth Seeded X-ray Laser

  3 x 1011 photons/pulse at 1 kHz = 3 x 1014 ph/sec

  Bandwidth seeding: 100 fs = 20 meV (l = 0.1nm)
      1013 ph/sec at 1 meV resolution

  Bandwidth seeding: 1 ps = 2 meV
      1014 ph/sec at 1 meV

  Compare with 109 ph/sec at 3rd Gen Sources

       An intensity gain of 4-5 orders of magnitude will
         revolutionize the study of the dynamics of
                      condensed matter
                      MIT X-ray Laser Project
Transient Grating Spectroscopy
    or Time-Dependent IXS




                  Keith Nelson, Chemistry Department, MIT
                                    MIT X-ray Laser Project

Next-generation backscattering analyzers



                  (Yuri Shvyd’ko, DESY)




 •Variable resolution down to 0.1 meV
 •Decouple the incident energy and the resolution
 •Less demanding temperature stability
 •Using sapphire, any incident energy can be selected
                                   MIT X-ray Laser Project

Accessible phase space


            Inelastic Scattering



          Time-Dependent Methods
                                   MIT X-ray Laser Project

The Potential of a Transform-Limited X-ray Laser for
              Inelastic X-ray Scattering
               Third Generation IXS

•1010 ph/sec in 1 meV bandwidth
•S/N still too low for many experiments
•Phenomena with DE < 1 meV not resolved by IXS
•Generally phenomena with 1 ns > Dt > 1 ps are inaccessible
             Bandwidth Seeded X-ray Laser
•Up to 1014 ph/sec in meV bandwidth
•Transform-limited pulses reach Heisenberg limit Dt Dw ~ p
•Time-dependent (or pump-probe) IXS for full t/E coverage
                                               MIT X-ray Laser Project

Photon pulses would be “transform-limited” satisfying the
 Uncertainty Principle in all six phase-space dimensions


   Transverse Phase Space
     Dx , Dy ~ 100 microns
     Dkx , Dky ~ 10-5 nm-1




                         Longitudinal Phase Space
                      Dt ~ 1fs - 1ps   Dw ~ 2eV - 2meV


   Note that all 1011 to 1014 photons in each pulse would
              occupy the same quantum state
                                     MIT X-ray Laser Project

 To realize such a source, the most sophisticated laser
and accelerator technology must be integrated together.
        The laser generates the coherent signal

                                 MIT Ultrafast Laser Group
                                 Franz Kaertner, Erich Ippen, et al



       An accelerated electron beam amplifies and
        frequency shifts the laser radiation

                                  MIT Bates Laboratory
                                  William S. Graves et al
                                      MIT X-ray Laser Project

        Self-Amplified Spontaneous Emission (SASE)

e-
                  ~100 fs




     Argonne APS first demonstrates
     SASE at optical wavelengths

          Gain of 107

     LCLS project at SLAC aims to
     demonstrate SASE at 0.15 nm
                                      MIT X-ray Laser Project

A SASE FEL amplifies random electron density modulations




                t (fs)                    Dw/w (%)

          The SASE radiation is powerful, but noisy!

     One solution: Impose a strong coherent modulation with
                     an external laser source
                                         MIT X-ray Laser Project

            Brookhaven laser seeding technology
   e-
Laser                                                              output

800 nm                                                             266 nm
              Modulator        Buncher          Radiator


   High Gain Harmonic
   Generation (HGHG)                             HGHG


  •Suppressed SASE noise
  •Amplified coherent signal                        SASE x105

  •Narrowed bandwidth
  •Shifted wavelength
                                                 MIT X-ray Laser Project

   To Produce Transform-Limited Pulses below 10 nm

          •Must get powerful short-wavelength seeds using High
                     Harmonic Generation methods

        •Then use ―cascaded‖ High Gain Harmonic Generation
                          methods in FEL

                  Stage 1 output at     Stage 2 output at      …Nth stage
                  5w0 seeds 2nd stage   25w0 seeds 3rd stage   output at 5Nw0
Input
seed w0
                 1st stage                 2nd stage           …Nth stage
                                    MIT X-ray Laser Project
           Two different seeding regimes
 Seeding for short (1 fs) pulses—bandwidth of a few eV




 Seeding for narrow (meV) bandwidth—pulse lengths 0.1 – 1.0 ps
                                                                                        MIT X-ray Laser Project


Superconducting linac                                                                                  Developed
technology is essential                                                                                at DESY


 High pulse rates provide for many independent beamlines
 CW operation provides much greater beam stability
 Most important is minimizing electron arrival time jitter
                                6.0
                                                                              Copper linacs like Bates or LCLS have
                                                                              jitter of 100’s of femtoseconds
  Phase: Klystron - MOA (deg)




                                5.5


                                5.0                                           Seeded FEL requires 10 fs timing stability
                                                                              at short wavelengths
                                4.5       σ = 0.14° (150 fs)

                                          Measured inside 10 s window
                                4.0
                                                                              CW Superconducting cavities will have
                                      0    100       200       300      400   much less phase jitter
                                                   Time (s)
MIT X-ray Laser Project
MIT X-ray Laser Project
                                                                        MIT X-ray Laser Project

                       Main oscillator
                                               Fiber link synchronization


               Seed
                       UV Hall              Pump
                                                                     X-ray Hall
                                                            Seed                         Pump
               laser                        laser           laser                        laser
                           Undulators
                            200 nm
                                                                    Undulators
                             30 nm                                    1 nm
Injector
  laser                      10 nm                                   0.3 nm




                             SC Linac                    0.3 nm               SC Linac               0.1 nm
       1 GeV       2 GeV                    4 GeV


                                           10 nm
                                                                                                 Upgrade: 0.1 nm
                                                                                                    at 8 GeV
                                           3 nm


                                           1 nm
                                         Undulators
                             Seed                         Pump
                             laser                        laser
                                     Nanometer Hall
                                                             MIT X-ray Laser Project
          Narrow bandwidth performance for MIT and LCLS
                     12.4 eV       124 eV    1.24 keV   12.4 keV       LCLS performance from
                                                                       SLAC website parameter
                                 MIT UV                                table.
                               Dt = 200 fs                             MIT beamlines are 1 kHz.
                               Dw = 10 meV                             LCLS is 120 Hz.
                                                                       MIT covers wide spectrum
                                              MIT X-ray                simultaneously with
                                             Dt = 200 fs               multiple undulators.
Photons per second




                                             Dw = 10 meV               LCLS limited by undulator
                                                                       lattice to spectrum shown,
                                                                       must tune energy for
                                                          LCLS         different wavelengths.
                                                        Dt = 200 fs    Note steep falloff at short
                                                        Dw = 4 eV      wavelength for MIT due to
                                                                       gun performance and 4
                                                                       GeV energy.
                                                             MIT
                                                                       Change in performance at
                                                        3rd harmonic   5 nm is due to beam
                                                                       energy change from 1
                                           LCLS                        GeV at longer
                                       Dt = 200 fs                     wavelengths to 4 GeV.
                                       Dw = 10 meV                     This is conservative
                                                                       spectral flux density for
                                                                       MIT. A 2 ps long pulse
                                                                       would have 10 times the
                                  Wavelength (m)                       flux in 1/10 the bandwidth.
                                                                          MIT X-ray Laser Project
                     Short-pulse performance for MIT and LCLS
                                  12.4 eV        124 eV        1.24 keV          12.4 keV
                                                                                            Photons per second
                                                                                            assuming FEL output from
                                                                                            the short pulselengths
                          30 fs         MIT UV                                              shown. LCLS uses electron
                                                                                            beam slicing, MIT uses short
                                                                                            seed pulse.
                                                                                            MIT beamlines are 1 kHz.
                                        10 fs                                               LCLS is 120 Hz.
Photons per second




                                                                                            Dots are minimum FWHM
                                                             MIT                            pulselengths using FEL gain
                                                             X-ray                          bandwidth.
                                                                          1 fs              CPA pulselength accounts
                                                    3 fs                  CPA               for bandwidth and slippage.
                                                                                            CPA can be used at longer
                                                                                            wavelengths also. Slippage
                                                           LCLS                             limits the min pulse length to
                                                                                            be near the values shown at
                                                                                            each wavelength. The pulse
                                                                  1 fs                      intensity would be increased
                                                                                            by 1-2 orders of magnitude.

                                                                            0.5 fs          Bandwidth ranges from 5e-4
                                                                                            at 0.3 nm to 1e-2 at 200 nm.


                                       Wavelength (m)
                                            MIT X-ray Laser Project

Chirped Pulse Compression
                                             l = 2d
E
           20 meV


    2eV                                      lf lf i li
                                                 l
             100 fs

                      t
          For compression: 100 fs to 1 fs
          •Energy chirp/bandwidth > compression      df di
          •Reflectivity/layer< pulse chirp
          •But extinction depth~ few pulse lengths
          •Crystal chirp > pulse chirp
                                      MIT X-ray Laser Project

MIT Ultrafast Laser Group is developing:
    Overall laser timing and synchronization below 10 fs
                                      MIT X-ray Laser Project

MIT Ultrafast Laser Group is developing:
     RF phase control and stabilization
                                    MIT X-ray Laser Project

MIT Ultrafast Laser Group is developing:
   Powerful short wavelength seed lasers




                                            Phase
                                            Controlled
                                            5fs, 5mJ,
                                            1 kHz
                                    MIT X-ray Laser Project

MIT Ultrafast Laser Group is developing:
High-Harmonic Generation with Noble gas jets (He, Ne, Ar, Kr)

      Phase
      Controlled                       XUV @ 3 – 30
      5fs, 5mJ,                        nm
      1 kHz
                                       h = 10-8 - 10-5

                                              t  Propagation
                                              Recombination
                                     0
                                              wXUV                        x

                                     -Wb
                                                          tb
                                                  Ionization

                                     Energy
                                                   Laser electric field
                                            MIT X-ray Laser Project
A focused, concept-driven R&D program is a pre-requisite
    to an X-ray Laser User Facility incorporating many
         beamlines and seeding for full coherence
  Execute the critical laser related R&D to achieve necessary seed
 power, wavelength, pulse duration, and timing synchronization
  Work in collaboration with ANL, BNL, DESY to demonstrate seeding
 and cascaded HGHG. Establish a facility at 100 nm for experimental use
  Work in collaboration with DESY, Jlab, Cornell and others to optimize
 SC RF technology for CW applications w/ 10-5 amplitude control
  Explore a new concept pioneered at Bates for greatly simplifying RF
 systems and significantly reducing costs
  Develop high rep-rate, high-brightness photoinjector and drive laser in
 collaboration with LBNL
 Collaborate with ANL and NHFML to optimize the LCLS undulator
 design for variable gap performance
                                                 MIT X-ray Laser Project

               Critical DUVFEL Experiments
1. Cascaded HGHG experiment. Future x-ray FEL facilities that generate fully
   coherent radiation will require multiple cascaded HGHG stages starting from a
   long wavelength seed laser.
2. Chirped pulse amplification using HGHG. Seed FEL with frequency-chirped
   laser, amplify, and compress optical pulse to produce high power, short time
   duration output.
3. Start-to-end simulation using measured parameters. Include beam-based
   measurements of injector RF fields, thermal emittance, photocathode laser time
   profile, undulator fields, and seed properties. Test codes including parmela, MAD,
   elegant, and ginger.
4. Seeding with HHG. The Quantum Optics group at MIT is developing high
   harmonic generation from conventional lasers for use as a short wavelength (10-
   100 nm) seed. This has advantages over seeding with low harmonics including
   requiring fewer HGHG stages, and generating pulse lengths approaching 1 fs.
                                          MIT X-ray Laser Project

   Develop a risk-based prototyping program for all critical components
   Plan for a broad and inclusive User Program appropriate for a
  National Facility
   Educate the scientific community to develop beamline concepts and
  execute the necessary R&D to support 10 initial beamlines
   Leverage this R&D program with MIT educational programs to
  involve graduate students, undergraduates, K-12 students and
  teachers
And finally….
   Develop the overall conceptual design, cost and schedule
  data necessary for a decision to construct

     We propose a 3-year $15M collaborative effort
                   centered at MIT
                                           MIT X-ray Laser Project
Conclusions: Technical
 A multi-beamline X-ray Laser User Facility can be conceived based on
existing technology combined with a focused 3-year R&D program.
 A modular approach with 2 or more stages with increasing linac energy
would be a systematic approach, establishing capabilities and proving
technology at various cost/performance points versus wavelength.
 Lower emittance electron guns would have enormous impact, enabling
x-ray wavelengths to be reached at conventional (6-8 GeV) energies.
 Seeding technology would greatly improve performance with highly
synchronized transform-limited pulses, and seeding reduces undulator
gain lengths and associated costs.
 CW SC RF is probably essential for synchronization stability, and since
cryogenic costs rise rapidly with linac energy and gradient, the lower
electron energies achieved with lower emittance guns will be very
important. Possible pulse structures are strongly influenced by this choice.
                                               MIT X-ray Laser Project

Conclusions: Scientific
 Transform-limited beams from seeded sources will enable science well
beyond SASE, for example . . .
 Seeding for narrow bandwidth will enable pulses as long as 1 ps to have
a bandwidth of 2 meV. SASE sources monochromated to meV levels have
large fluctuations and low photon flux.
 Seeding with for short pulses using CPA combined with “compression
optics” may allow femtosecond pulses containing 1011 photons or more.
This is significantly higher than SASE and of crucial importance for
molecular imaging, and chemical dynamics studies.
 Finally, I believe that virtually all experiments carried out at 3rd generation
sources are easily accomplished on such a source at lower facility cost.
This will not be an exotic facility for only niche experiments, but represents
a source of extraordinary power and flexibility with which all x-ray
experiments possible can be done.

								
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