How to Make Light

Gwyn P. Williams

Jefferson Lab12000 Jefferson Avenue - MS 7A

Newport News, VA 23606 gwyn@mailaps.org

Jefferson Lab Summer Lecture July 21, 2008

Outline of Talk

1. Motivation – why do we need bright light?

2. How do we make ultrabright light sources?

……what is brightness anyway?

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.

Need to understand small things

A nanosytem - Brownian motion.

Very small is different than big

Modern nanotechnology will require an understanding of small, isolated systems

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.

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.

What are some examples of small systems?

Molecular junction.

(a) Freeze motion

(b) Study “dynamics” in time domain

Fast Cameras

Sizes and Time-scales……“seeing atoms”

Area of atom is 10-20 m2

Area of focus of 0.1 nm beamof 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!

0.1 nanometer

t = 10-14 secs (10fs)

Development of Brightness of Light Sources

1960 1970 1980 1990 2000 2010105

107

109

1011

1013

1015

1017

1019

1021

1x1023

1x1025

1x1027

1x1029

1x1031

1033

4th Gen.Multiparticlecoherentenhancement

3rd. Gen.original design

2nd. Gen.

1st. Gen. Synch. Rad.

GROWTH IN AVERAGE X-RAY SOURCE BRIGHTNESS

(Photons/sec/0.1%bw/sq.mm/mrad2)

Calendar Year

1960 1970 1980 1990 2000 2010105

107

109

1011

1013

1015

1017

1019

1021

1x1023

1x1025

1x1027

1x1029

1x1031

1033

MOORE'S LAWComputer Component DoublingEvery 18 months

4th Gen.Multiparticlecoherentenhancement

3rd. Gen.original design

2nd. Gen.

1st. Gen. Synch. Rad.

GROWTH IN AVERAGE X-RAY SOURCE BRIGHTNESS

(Photons/sec/0.1%bw/sq.mm/mrad2)

Calendar Year

Development of Brightness of Light Sources

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.

LASERLIGHT

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

Accelerator-based light sources have no limitations…..

Synchrotrons, Free Electron Lasers

• Tunable• Short wavelengths (x-rays)• High power and brightness

How do these accelerator-based light sources work?

electron

electricfield

Accelerator-based Light Sources – physics

4Larmor's Formula: Power (cgs units)

2 2

32

3e ac

Maxwell’s equation

" "Free oPE

t tH J

e- light

e is charge on electrona is accelerationc is speed of light is relativistic mass increase

2e-

light

How do we make light sources more powerful?

42 23

2( )3

2e ac

Power

e is charge on electrona is accelerationc is speed of light is relativistic mass increase

4 times the power!!!

25102 ddE

J/cm-1/electron

from Richard Sheffield LANL

Schematic of next generation light source

LASER

laser “seed”optional

Principle of Jefferson Lab’s Energy Recovered Linac / FEL

JLab’s Existing 4th Generation Light Source

E = 150 MeV135 pC pulses up to 75 MHz(20)/120/1 microJ/pulse in (UV)/IR/THz250 nm – 14 microns, 0.1 – 5 THz

All sources are simultaneously produced for pump-probe studies

Light Sources – “The World Stage”

Light Sources – “The World Stage”

JLAB THz

JLAB FEL LCLS….

FLASH21st . Century Light Source

So why haven't they been built?

Shorter wavelengths isky and expensive using present technology!

1E-4 1E-3 0.01 0.1 1 10 100 1000 1000010

4

106

108

1010

1012

1014

1016

1018

1020

1022

1024

1x1026

1028

1x1030

4th. Generation

3rd. Generation

2nd. Generation

Gwyn Williams - file brt_1.basNov. 2007

Ave

rage

Brig

htne

ss

Pho

tons

/sec

/0.1

%B

W/m

m2/s

r

Photon Energy (eV)

$ 500M

$ 250M

$ 120M

$ 60M

SRF Linac cost

Operating and Future ERLsOperating and Future ERLs

Operating ERLs

ERL Test Facilities

ERL Conceptual designs

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

1. FZR-Dresden, IR/THz, operational

2. Budker Institute, Novisibirsk, Russia, THz ERL operational

3. FLASH, Hamburg, Germany, soft x-ray, operational

4. Daresbury & Rutherford UK, THz-x-ray, proposal in process

5. STAR, Berlin, Germany, soft x-ray, proposal

6. Paul Scherrer Inst. Switzerland, hard x-ray, proposal

7. Maxlab, Lund, Sweden, soft x-ray, proposal

8. XFEL, Hamburg Germany, hard x-ray, European proposal

9. XFEL, Spring-8, Japan

Next Generation Light Sources – non USA Programs

Undulator and linear accelerator at Jefferson Lab

Wavelength 20 cmNumber of periods 12 ea.Gap 26 mm

Superconducting Radio-Freq. Linac

InjectorCryomodule

Wiggler

Beam Stop Gun

Periodic Magnetic Field

Electron Beam

Total Reflector

Niobium SRF Cavity withOscillating Electromagnetic Field

Schematic of JLab 4th. Gen. Light Source Operation

Light Output

Electron Beam

Drive Laser

Output Mirror

Laser Wavelength ~ Wiggler wavelength/(2Energy)2

JLab THz

Synchrotrons

Globar

JLab FEL

Table-top sub-ps lasers

FEL proof of principle:Neil et al. Phys. Rev.Letts 84, 662 (2000)

THz proof of principle:Carr, Martin, McKinney, Neil, Jordan & WilliamsNature 420, 153 (2002)

Jefferson Lab facility unique spectroscopic range

One of the first areas of impact of next generation light source technology –

Terahertz

What is Terahertz Light?

Tom Crowe, UVa

Electronics - radios Photonics – light bulbs

Frequency THz

Why is Terahertz Light new?

JLab THz

High Power THz Light is New - Nature March 2007

Tonouchi Nature Photonics 1, 97 (2007)

Photonics- lightsources

Electronics - radios

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.

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

Clery, Science 297 763 (2002)

Security – hidden weapons

30 GHz NOT THz

Security – hidden non-metallic weapons

David Zimdars SPIE 5070 (2003)

Security – hidden weapons, explosives

Explosive “fingerprints”

THz Visible

Security – fingerprint of anthrax proxy

Security – hidden bio-agents, explosives

David Zimdars, John Federici

Operated by the Southeastern Universities Research Association for the U.S. Department of Energy

Thomas Jefferson National Accelerator Facility

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

Medical – improved dental imaging

A tooth cavity shows up clearly in red. Teraview Ltd.

Conclusion

Bright Light has a Bright Future.

Quest is now on to shorten wavelength.

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.