# Presentation: 757590

## 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 R&D Proposal

**MIT X-ray Laser R&D Proposal**

- Contact: David E. Moncton, Director

- T

- elephone:

- 617

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- 253

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- 8333

- E

- -

- mail:

- dem@

- mit.edu

- website:

- http://mitbates.mit.edu/xfel/indexpass.htm

-   Bates Senior Staff

- Contributors

-   Manouchehr Farkhondeh

- William M. Fawley

- James Fujimoto

-   Jan van der Laan

- Erich Ippen

-   Christoph Tschalaer

- Ian McNulty

- Denis B. McWhan

-   Fuhua Wang

- Jianwei Miao

- Michael Pellin

-   Abbi Zolfaghari

- Mark Schattenburg

- Gopal K. Shenoy

-   Townsend Zwart

- 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

## 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  **

**Condensed Matter Physics**

**Atomic Physics**

**Fundamental Physics**

**Biology **

- Full transverse coherence

- Milli-volt bandwidths

- Full quantum degeneracy

- High electric field

## Photon pulses would be  “transform-limited” satisfying the

**Uncertainty Principle in all six phase-space  dimensions**

- Transverse Phase Space
******x********y ~ 100 microns    **
******k****x********k****y ****~ 10****-5**** nm****-1**

- Longitudinal Phase Space
******t ~ ********fs********1ps     ********eV********2meV**

- Note that all 1011 to 1014 photons in each pulse would occupy the same quantum state

## Probes charge-neutral excitations:

- Probes charge-neutral excitations:
-  Phonons, diffusive modes, orbitons, superconducting gaps...
-  Excitons, plasmons, particle-hole creation, interband transitions...

**Inelastic X-ray Scattering (IXS)**

## Existing 3rd Generation  IXS Beamlines

- _ESRF_

- _APS_

- 3 Beamlines with meV resolution, 2 more soon
- 1 Beamline with 100 meV resolution
- 2 Beamlines with eV resolution

-      ESRF                      APS                    Spring-8

## IXS with 3rd Generation Synchrotron Sources

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

- TiOCl

- E. Isaacs, Y. Lee, D. Moncton

## 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  ( = 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

## Transient Grating Spectroscopy

**Transient Grating Spectroscopy**
**or Time-Dependent IXS**

- Keith Nelson, Chemistry Department, MIT

## Next-generation backscattering analyzers

**Next-generation backscattering analyzers**

- 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

- (Yuri Shvyd’ko, DESY)

## Accessible phase space

**Accessible phase space**

## The Potential of a Transform-Limited  X-ray Laser for Inelastic X-ray Scattering

- 1010  ph/sec in 1 meV bandwidth
- S/N still too low for many experiments
- Phenomena with  E < 1 meV not resolved by IXS
- Generally phenomena with  1 ns > t > 1 ps are inaccessible

**Bandwidth Seeded X-ray Laser**

- Up to 1014 ph/sec in meV bandwidth
- Transform-limited pulses reach Heisenberg limit t ~ 
- Time-dependent (or pump-probe) IXS for full t/E coverage

**Third Generation IXS**

## Photon pulses would be  “transform-limited” satisfying the

**Uncertainty Principle in all six phase-space  dimensions**

- Transverse Phase Space
******x********y ~ 100 microns    **
******k****x********k****y ****~ 10****-5**** nm****-1**

- Longitudinal Phase Space
******t ~ ********fs********1ps     ********eV********2meV**

- Note that all 1011 to 1014 photons in each pulse would occupy the same quantum state

## To realize such a source, the most sophisticated laser and accelerator technology must be integrated together.

## Self-Amplified Spontaneous Emission  (SASE)

## One solution:  Impose a strong coherent modulation with an external laser source

**A SASE FEL amplifies random electron density modulations**

## Brookhaven laser seeding technology

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

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

- Then use “cascaded” High Gain Harmonic Generation methods in FEL

## 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

##  High pulse rates provide for many independent beamlines

-  CW operation provides much greater beam stability
-  Most important is minimizing electron arrival time jitter

- Seeded FEL requires 10 fs timing stability at short wavelengths

- CW Superconducting cavities will have much less phase jitter

## Slide 21

## Slide 22

## Slide 23

## Narrow bandwidth performance for MIT and LCLS

- MIT beamlines are 1 kHz.  LCLS is 120 Hz.
- MIT covers wide spectrum simultaneously with multiple undulators.
- LCLS limited by undulator lattice to spectrum shown, must tune energy for different wavelengths.
- Note steep falloff at short wavelength for MIT due to gun performance and 4 GeV energy.
- Change in performance at 5 nm is due to beam energy change from 1 GeV at longer wavelengths to 4 GeV.
- This is conservative spectral flux density for MIT.  A 2 ps long pulse would have 10 times the flux in 1/10 the bandwidth.

**Narrow bandwidth performance for MIT and LCLS**

## Short-pulse performance for MIT and LCLS

- Photons per second assuming FEL output from the short pulselengths shown.  LCLS uses electron beam slicing, MIT uses short seed pulse.
- MIT beamlines are 1 kHz.  LCLS is 120 Hz.
- Dots are minimum FWHM pulselengths using FEL gain bandwidth.
- CPA pulselength accounts for bandwidth and slippage.
- CPA can be used at longer wavelengths also.  Slippage limits the min pulse length to be near the values shown at each wavelength.  The pulse intensity would be increased by 1-2 orders of magnitude.
- Bandwidth ranges from 5e-4 at 0.3 nm to 1e-2 at 200 nm.

**Short-pulse performance for MIT and LCLS**

## di

**Chirped Pulse Compression**

**d****i**

**d****f**

******d**

- For compression: 100 fs to 1 fs
- Energy chirp/bandwidth > compression
- Reflectivity/layer< pulse chirp
- But extinction depth~ few pulse lengths
- Crystal chirp > pulse chirp

## MIT Ultrafast Laser Group is developing:

-  Overall laser timing and synchronization below 10 fs

## MIT Ultrafast Laser Group is developing:

-  RF phase control and stabilization

## MIT Ultrafast Laser Group is developing:

-  Powerful short wavelength seed lasers

**Phase Controlled****5fs, 5mJ,****1 kHz**

## High-Harmonic Generation with Noble gas jets (He, Ne, Ar, Kr)

**Phase Controlled****5fs, 5mJ,****1 kHz**

**MIT Ultrafast Laser Group is developing:**

## 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

## Critical DUVFEL Experiments

**Chirped pulse amplification using HGHG**.  Seed FEL with frequency-chirped laser, amplify, and compress optical pulse to produce high power, short time duration output.
**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.
**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.

**Critical DUVFEL Experiments**

## And finally....

-  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**   **

** ****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

## 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.

## 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.