Gwyn P. Williams

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How to Make Light

• Gwyn P. Williams
• Jefferson Lab
• 12000 Jefferson Avenue - MS 7ANewport News, VA
  23606 gwyn_at_mailaps.org

Jefferson Lab Summer Lecture July 21, 2008
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Outline of Talk

• 1. Motivation why do we need bright light?
• How do we make ultrabright light sources?
• what is
  brightness anyway?

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Need to understand small things
Very small is different than big
Typical thermodynamic system - heat moves from
hot (boiler) to cold (condenser) and work is
extracted.
Small is different. Small things such as pollen
grains in a water solution are endlessly buffeted
by the random motion of the water molecules.
(This is termed Brownian motion). Macroscopic
machines like steam engines are far too
massive to be affected by these small
fluctuations. We cannot calculate the
power/efficiency trade-off for a nanomachine or
derive design rules. Neither thermodynamics nor
stationary-state quantum mechanics helps.
Molecular junction.
A nanosytem - Brownian motion.
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What are some examples of small systems?
Modern nanotechnology will require an
understanding of small, isolated systems
A powerful molecular motor (yellow) translocates
the twisted strands of DNA (right) of a virus
into a protein capsid. By using optical tweezers
to pull on the DNA while it is being packed, it
was determined that the motor can pack DNA to a
pressure of about 60 atmospheres, 10x that of a
champagne bottle.
Electron transport has been observed across
molecules with only a few monomers (a few
Angstrom). Charge transfer through single
molecular devices is presently one the most
fascinating and fastest developing fields in the
range between mesoscopic physics and chemistry.
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Fast Cameras
(a) Freeze motion
(b) Study dynamics in time domain
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Sizes and Time-scalesseeing atoms
Area of atom is 10-20 m2
Area of focus of 0.1 nm beam of light is 10-20 m2
Need 1012 photons/sec to get good data, into this
area - which means a desired BRIGHTNESS of 1026
photons/sec/mm2/mrad2 Brightness is photon
flux/(area x angle)
or photons on
target!
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Development of Brightness of Light Sources
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Development of Brightness of Light Sources
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Back to lasers - conventional types of lasers

• 1. Solid State
• 2. Gas
• 3. Excimer
• 4. Dye
• 5. Semiconductor
• 6. Fiber
• All work with a medium in a cavity.

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LASER LIGHT
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Conventional lasers have limitations

• Not tunable
• Limited availability of different wavelengths
  from catalogs
• Output typically limited to a few watts
• No short wavelengths x-rays

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Accelerator-based light sources have no
limitations..

• Synchrotrons, Free Electron Lasers
• Tunable
• Short wavelengths (x-rays)
• High power and brightness

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How do these accelerator-based light sources work?
electric field
electron
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Accelerator-based Light Sources physics
e is charge on electron a is acceleration c is
speed of light ? is relativistic mass increase
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How do we make light sources more powerful?
2e-
light
e is charge on electron a is acceleration c is
speed of light ? is relativistic mass increase
4 times the power!!!
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Schematic of next generation light source
LASER
from Richard Sheffield LANL
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Principle of Jefferson Labs Energy Recovered
Linac / FEL
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JLabs Existing 4th Generation Light Source
E 150 MeV 135 pC pulses up to 75 MHz (20)/120/1
microJ/pulse in (UV)/IR/THz 250 nm 14 microns,
0.1 5 THz
All sources are simultaneously produced for
pump-probe studies
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Light Sources The World Stage
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Light Sources The World Stage
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So why haven't they been built?

• Shorter wavelengths isky and expensive using
  present technology!

500M
SRF Linac cost

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Operating and Future ERLs
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Next Generation Light Sources USA Programs

1. Jefferson Lab, IR/THz ERL, operational
2. LCLS, Stanford, USA, hard x-ray, DOE-BES under
   construction
3. Cornell University, hard x-ray ERL, proposal to
   NSF, initial funding
4. Florida State University, IR/THz ERL, proposal to
   NSF, initial funding
5. WiFEL, Stoughton, Wisconsin, soft x-ray, proposal
   to NSF
6. Advanced Light Source, Berkeley, soft x-ray,
   proposal to DOE
7. Advanced Photon Source, Argonne, hard x-ray ERL,
   proposal to DOE
8. LSU, THz soft x-ray, white paper preparation to
   State and DOE
9. The Light Source of the Future (LSF), DOE-BES,
   TBD

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Next Generation Light Sources non USA Programs

• FZR-Dresden, IR/THz, operational
• Budker Institute, Novisibirsk, Russia, THz ERL
  operational
• FLASH, Hamburg, Germany, soft x-ray, operational
• Daresbury Rutherford UK, THz-x-ray, proposal in
  process
• STAR, Berlin, Germany, soft x-ray, proposal
• Paul Scherrer Inst. Switzerland, hard x-ray,
  proposal
• Maxlab, Lund, Sweden, soft x-ray, proposal
• XFEL, Hamburg Germany, hard x-ray, European
  proposal
• XFEL, Spring-8, Japan

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Undulator and linear accelerator at Jefferson Lab
Wavelength 20 cm Number of periods 12
ea. Gap 26 mm
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Superconducting Radio-Freq. Linac
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Schematic of JLab 4th. Gen. Light Source Operation
Niobium SRF Cavity with Oscillating
Electromagnetic Field
Electron Beam
Drive Laser
Light Output
Total Reflector
Output Mirror
Periodic Magnetic Field
Electron Beam
Laser Wavelength Wiggler wavelength/(2Energy)2
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Jefferson Lab facility unique spectroscopic range
JLab FEL
JLab THz
FEL proof of principle Neil et al. Phys.
Rev.Letts 84, 662 (2000)
Table-top sub-ps lasers
Synchrotrons
Globar
THz proof of principle Carr, Martin, McKinney,
Neil, Jordan Williams Nature 420, 153 (2002)
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One of the first areas of impact of next
generation light source technology Terahertz
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What is Terahertz Light?
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Why is Terahertz Light new?
Photonics light bulbs
Electronics - radios
Frequency THz
Tom Crowe, UVa
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High Power THz Light is New - Nature March 2007
JLab THz
Photonics - light sources
Electronics - radios
Tonouchi Nature Photonics 1, 97 (2007)
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What is Unique about Terahertz Light?

• THz light passes through many materials, such
  as
• packaging material, clothing, carpet, walls.
• THz light is non-ionizing unlike x-rays.
• THz light can recognize and distinguish
  materials that
• x-rays cannot, such as plastics proteins.
• THz light allows high speed safe
  communications.
• - Tera is 1000 times faster than Giga
• THz does not pass through metal and water, and
  will always
• be complimentary to x-rays.

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Why make Terahertz Light?

• Many applications, new discoveries every
  month.
• Security
• Medical screening (skin cancer)
• Pharmaceuticals (drug verification and testing)
• Non-destructive evaluation
• Environmental monitoring
• High speed communication

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Security hidden weapons
30 GHz NOT THz
Clery, Science 297 763 (2002)
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Security hidden non-metallic weapons
David Zimdars SPIE 5070 (2003)
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Security hidden weapons, explosives
THz
Visible
Explosive fingerprints
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Security fingerprint of anthrax proxy
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Security hidden bio-agents, explosives
David Zimdars, John Federici
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Medical cancer screening
Basal cell carcinoma shows malignancy in red.
Teraview Ltd. 1 mW source images 1 cm2 in 1
minute 100 W source images whole body (50 x
200cm) in few seconds
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Medical improved dental imaging
A tooth cavity shows up clearly in red. Teraview
Ltd.
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Conclusion
Bright Light has a Bright Future. Quest is now
on to shorten wavelength.
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FEL Team at JLab
This work supported by the Office of Naval
Research, the Joint Technology Office, the
Commonwealth of Virginia, the Air Force Research
Laboratory, Army Night Vision Lab, and by DOE
Contract DE-AC05-84ER40150.