Laser Acceleration Experiments at ORION Professor Robert L. Byer Stanford University Dept. Applied Physics 2 nd ORION Workshop February 18-20, 2003.

Laser Acceleration Experimentsat ORION

Professor Robert L. Byer

 Stanford University

Dept. Applied Physics

2nd ORION Workshop February 18-20, 2003

OutlineThe Promise of Laser Acceleration

Recent Progress in Lasers

Recent Laser Acceleration Mechanisms

Low Field (ao<<1) Acceleration and High Field (ao1)

Experiments in Laser Acceleration

Future Issues

2nd ORION Workshop February 18-20, 2003

Lasers produce unequalled energy densities and electric fields

Very short pulses permit higher surface electric fields without breakdown

Very short wavelengths (compared to microwaves) naturally lead to:

Sub-femtosecond electron bunches sub-fs radiation pulses

Very short wavelengths require:

Very small emittance beams radiation sources are truly point-like

Lasers development is strongly driven by industry

Lasers are a $4.8B/year market (worldwide), with laser diodes accounting for 59%, DPSS lasers $0.22B/year, and CO2 lasers $0.57B/year [1] (in contrast, the domestic microwave power tube market is $0.35B/year, of which power klystrons are just $0.06B/year[2]).

Peak Powers of TW, average powers of kW are readily available from commercial products

The market’s needs and accelerator needs overlap substantially: Cost, reliability, shot-to-shot energy jitter, coherence, mode quality are common to both

The Promise of Laser Acceleration

[1] K. Kincade, “Review and Forecast of the Laser Markets”, Laser Focus World, p. 73, January, (2003).

[2] “Report of Department of Defense Advisory Group on Electron Devices: Special Technology Area Review on Vacuum Electronics Technology for RF Applications”, p. 68, December, (2000).

High Gradient Requires High Energy Density

*28.5 GeV, 1e10 ppp, x x (20 for SPPS) beam

**350 MeV, 1e10 ppp, 1 x 1 x 1 mm beam

Source Wavelength

cm cm mm nmE. Colby

Pf 2

1. Power scalability to hundreds for Watts of average power per laser2. Wall-plug efficiency > 20%3. Mass producible, reliable and low-cost 4. Ultra low optical phase noise

Existing widespread commercial ultra-fast laser systems: Ti:sapphire Poor optical efficiency poor wall-plug efficiencyLow saturation low power systems (typically few Watts per laser)Large scale multi-component systems that require water coolingHigh costs systems (~100 k$/laser of ~1Watt avg. power)

Requirements for future ultra-fast lasers for particle accelerators

High average power ultra-fast lasers

Driving Applications

Industry and Basic ResearchMaterials Processing, ultrafast laser machining, via drilling, medical therapeutics, entertainment, image recording, remote sensing

DefenseCoherent laser radar, remote wind sensing, remote sensing of “smart dust”, trans-canopy ranging, and stand-off coherent laser inspection of laminated-composite aircraft components

Yb:KGd(WO4)2 slope efficiency 82.7% [Opt. Lett., 22 (17) p.1317, Sept. (1997)]limiting electrical efficiency of 41% (assuming 50% efficient pump diode)

Yb:KY(WO4)2 slope efficiency 86.9% [Opt. Lett., 22 (17) p.1317, Sept. (1997)] limiting electrical efficiency of 43% (assuming 50% efficient pump diode)

Candidate laser host materials for ultra-fast high-power lasers

Monocrystalline materials

Polycrystalline materialsNd:YAGNd: Y2O3

Cr2+:ZnSe Nd:Y3ScxAl(5-x)O12

•Better homogeneity of dopant•Lower fabrication cost•Possible tailoring of dn/dT•Single crystal growth still possible

Materials with low quantum defect, excellent slope efficiency, and good thermal conductivity

300W, e=50%, =780-1000 nm

3900 W, e=40%, =792-812 nm

Commercially Available High Efficiency Laser Diode Bars

Electrical Efficiency of Lasers

TUBES FELs LASERS(RF Compression, modulator losses not included)

SLAC PPM Klystron=2.624 cmt=3 secPave=27 kW=65%

Source Frequency [GHz]

Sou

rce

Ele

ctri

cal

Eff

icie

ncy

[%]

Yb:KY(WO4)2

Yb:YAGYb:Sr5(PO4)3F

Cr++:ZnSe

Er Fiber

Ti:Al2O3

CO2

Yb:KGd(WO4)2

=1.023slope=82.7%=41%t=176 fsecPave=1.1 WOpt. Lett., 25 (15), p.1119, August (2000).

Yb:KY(WO4)2

=1.028slope=86.9%=43%t=240 fsecPave=22.0 W

Opt. Lett., 27 (13), p.1162, July (2002).Yb:KGd(WO4)2

E. Colby

Interference fringes of carrier phase-locked white light continua generated from a Ti:Sapphire laser.

M. Bellini, T Hansch, Optics Letters, 25 (14), p.1049, (2000).

Laser phase-locking to a microwave reference with great stability has been demonstrated.

Photonics Trend: Custom Optical Media

• Photonic Crystals allow for tailoring optical properties to specific applications:– Nonlinearity: Spectroscopy,

wavelength conversion in telecom

– Dispersion: Telecom signal processing

– Large mode area: High power applications such as lithography and materials processing

• Custom optics require manufacturing techniques that can meet tight tolerances

PCF structures vary according to application: (a) highly nonlinear fiber; (b) endlessly single-mode fiber; (c) polarization maintaining fiber; (d) high NA fiber. From René Engel Kristiansen (Crystal Fibre A/S), “Guiding Light with Holey Fibers,” OE Magazine June 2002, 25.

a b

c d

Fabrication Trend: Small Feature Size

• The integrated circuit industry drives development of ever-smaller feature size capability and tolerance– DUV, X-ray and e-beam lithography

– High-aspect-ratio etching using high-density plasma systems

– Critical Feature size control → 0.5 nm (/200) RMS by 2010 (’01 ITRS)

Demonstration of recent progress in lithography

•Infrastructure: 10,500-square-foot class 100 cleanroom

•Research includes a wide range of disciplines and processes

–Used for optics, MEMS, biology, chemistry, as well as traditional electronics

–Equipment available for chemical vapor deposition, optical photolithography, oxidation and doping, wet processing, plasma etching, and other processes

–Characterization equipment including SEM and AFM available

A $60-million dollar 120,000-square-foot photonics laboratory with 20 faculty, 120 doctoral, and 50 postdoctoral researchers, completed in 2004.Current Research:Diode Pumped Solid State LasersDiode pumped lasers for gravitational wave receiversDiode pumped Laser Amplfier StudiesQuantum Noise of solid state laser amplifiersAdaptive Optics for Laser Amplifier beam controlThermal Modeling of Diode Pumped Nd:YAG lasers

Laser Interferometry for Gravity Wave detectionSagnac Interferometer for Gravitational Wave DetectionLaser Inteferometer Isolation and Control StudiesInterferometry for Gravitational Wave DetectionTime and Frequency response characteristics of Fabry Perot Int.GALILEO research program: gravitational wave receivers

Quasiphasematched Nonlinear Devices Quasi Phasematched LiNbO3 for SHG of diode lasers, cw OPO studies in LiNbO3, and diffusion bonded, GaAs nonlinear materials

Semiconductor and Advanced Opto-electronics Material Capabilities at Stanford

Recent Progress and Proposals for Vacuum Laser Acceleration

Experiments

2nd ORION Workshop February 18-20, 2003

STELLA (Staged Electron Laser Acceleration) experiment at the BNL ATF(STI Optronics/Brookhaven/Stanford/U. Washington)

C O 2 la se r be a m

E L E C T R O NS P E C T R O M E T E R

IF E LA C C E L E R ATO R IF E L

B U N C H E R

4 6 M e V 0 .5 n C 2 m m m ra d 3 .5 p s

0 .6 G W , 1 80 p s

Steeringcoil

BPM

BPM

BPM

BPM

Focusingquadrupo les

S teeringcoil

Focusingquadrupo les

W. Kimura, I. Ben-Zvi, in proc. of Adv. Accel. Conc. Conf., Santa Fe, NM, 2000.

The Inverse Free Electron Laser

Energy

Energy

EnergyIncoming BeamOptically Modulated

Beam

Optically Accelerated Beam

z

Interferometric Acceleration(Inverse Transition Radiation Acceleration)

The laser beams are polarized in the XZ plane, and are out of phase by

Gradient limited to 70 MeV/m for[R. J. Noble, 2001].

Terminating Boundary

Terminating Boundary

E1

E2

E1z

E2z

E1x

E2x

x

E1x + E2x = 0

|E1z + E2z| > 0

no transverse deflection

nonzero electric field in the direction of propagation

Interaction Length : ~1000 ~0.1 ZR

Slit Width ~10

Slit Width ~10

Electron beam

Waist size: wo~100

Crossing angle:

Interferometric Accelerators(Inverse Transition Radiation)

T. Plettner, et al, “The LEAP Project”, DOE Review Slides, April 14, 2000.

Laser Electron Acceleration Project at Stanford/SLAC

TEM00 Linear polarization Gaussian

pulses, =0.8 m (Ti:Sapphire)

Laser Acceleration in Vacuum at Brookhaven-ATF

TEM*01 Radial polarization Gaussian

Pulses, =10.6 m (CO2)

Electron beam

V. Yakimenko, et al, from ATF User’s Meeting, January 31, 2002.

Laser Accelerator MicrostructuresStanford/SLAC, LEAPE163 (SLAC)

Electron beams

TIR Silicon at 1.06

TIR Silicon at 2.5

X. Lin, Phys. Rev. ST-AB, 4, 051301, (2001).

Photonic waveguides are the subject of intensive research, and can be designed to propagate only the accelerating mode.

P. Russell, “Holey fiber concept spawns optical-fiber renaissance”, Laser Focus World, Sept. 2002, p. 77-82.

TIR Fused Silica at 1.06

Semiconductor lithography is capable of highly accurate, complex structure production in materials with good damage resistance and at low cost.

S. Y. Lin et. al., Nature 394, 251 (1998)

Multicell Linear Acceleration Experiments

Inverse Cerenkov Acceleration in Waveguide (Unfolded Fabry-Perot Interferometer)

A. Melissinos, R. Tikhoplav (U. Rochester, Fermilab)

TEM01* mode

=1.0 m (Nd:YAG)

0.2 ATM

He

Status: Structure has been fabricated with 80% power transmission measured. Nd:YAG drive laser is under construction at Fermilab now.

Y-C. Huang, et al, Nat’l Tsinghua University. Images from ATF User’s Meeting, January 31, 2002.

Expected gain: 250 keV over 24cm.

ZnSe Lenses

Multicell ITR AcceleratorY.-C. Huang, NTHU, Taiwan

Active Medium(Cerenkov Amplifier in Overmoded Waveguide)

L. Schächter, Technion, Israel

Cerenkov radiation from trigger bunch stimulates emission from laser media, causing amplification of the Cerenkov wakefield. At an appropriate distance behind the trigger bunch, large acceleration fields are present.

Laser pump power

Trigger bunch

LASER MEDIA: Nd:YAG

LASER MEDIA: Nd:YAG

Accelerated bunch

Laser pump power

• Phase synchronism places tight constraints on material nonlinearity, nonuniformity, and on the geometric tolerances

High Field Acceleration MechanismsCombined Ponderomotive and Nonlinear

Compton Scattering

P. X. Wang, Y. K. Ho, et al, J. Appl. Phys. 91 (2) p. 856, (2002).

Ponderomotive Acceleration (Demonstrated)(CEA-Lemeil-Valenton)

G. Malka, E. Lefebvre, J. Miquel, Phys. Rev. Lett. 78, 3314 (1997).

a=3, =39o a=3, =46o a=2, =46o

ao~300

High Field Acceleration Mechanisms

G. Stupakov, M. Zolotorev, Phys Rev Lett 86 5274 (2001).

Ponderomotive Scattering with Deflection field to aid beam extraction

Y. Salamin, C. Keitel, Phys Rev Lett 88 095005 (2002).

Ponderomotive Acceleration and Focussing

a0~5

Bs

ao~68

Prospects for Producing Relativistic

Laser Fields•DPSS Ti:sapphire =0.8 m

•20 TW, 10 Hz, M2<1.5

•f/2 diffraction-limited power density:

9.4x1019 W/cm2 ao=6.6

7.5 m

2.5

m

Experiments in Laser AccelerationLaser accelerator proof-of-principle experiments typically:

• Have small apertures

Small transverse beam dimensions are needed

Small emittances

Strong focussing

• Are typically single-stage

Energy effects are small, requiring precision spectrometry

•Require optical bunching to be maintained throughout acceleration if multiple-stage

Path length control for both electrons and the laser pulses is required

•Interact ultrafast laser pulses (t~1 ps) with short (t~1 ps) electron bunches

Timing jitter of laser and electron beams must be small

Precision (~1-10ps) relative timing measurement is needed

•Interact small laser spots (wo20 m) with small electron beams (r 20 m)

Transverse spot jitter and laser pointing jitters must be small

Precision (~1 m) spot size and position measurement required near accelerator

Technical Questions•How can power-efficient coupling between laser and beam be accomplished?

•How do material properties such as material damage, thermal conductivity, media aging, thermal expansion, dn/dT (and so on) impact accelerator performance?

•What future laser progress in average power, peak power, and efficiency can be expected?

•How can tiny structures be fabricated?

•How can the extremely short, low charge bunches be diagnosed?

Some Application-Specific Questions

•Can a low- laser accelerator structure be made for ion acceleration?

•What do electron and ion sources for laser accelerators look like?

•What does a laser accelerator final focus look like?

What experiments can be done to address these questions at ORION?

2nd ORION Workshop February 18-20, 2003

We will focus on vacuum laser acceleration experiments.

What are the important technical issues effecting the usefulness of laser acceleration?

Which of these issues can be addressed by experiments at ORION?

If scalable, long-term concepts cannot be realized in experiments at ORION, can proof-of-principle experiments be devised which still address the key questions?

What beams, diagnostics, and resources (time, equipment, etc.) are needed?

Redwood Room “C”

Bob Byer, Yen-Chieh Huang, WG Leaders

2nd ORION Workshop February 18-20, 2003

Laser Acceleration Working Group

BACK-UP

SLIDES

Recent Progress in Optical Materials High Damage Threshold Materials

•Optical-quality CVD diamond

•ZnSe

High Thermal Stability Materials

•Ultra-high thermal stability optical materials (Photonics Jan 2003, p.158)

(factor of 2 better than Zerodur)

•+ve/-ve material sandwich that has =(1/n)*dn/dT+~0 (same article as above)

Lithographically Treatable Materials

•Silicon (>1500nm) Silica

•Optical ceramics Nd:YAG

Laser Linear Collider pre-Concept

CW InjectorWarm rf gun Cold Preaccelerator Optical Buncher433 MHz x 105 e-/macropulse (600 pulse/macropulse)N~10-11 m (but note Q/N ~ 1 m/nC)

Laser Accelerator1-2 G~1 GeV/m

Photonic Band Gap Fiber structures embedded in optical resonant rings

Permanent Magnet Quads (B’~1 kT/m)

Optical Debuncher Final Focus I.P.

…

…

Laser amplifier

PBG accelerator structure

Optical resonator

An Acceleration Unit

Phase control

Stanford Research Program (DARPA)

A. High Average Power CW Lasers

B. High energy Yb:YAG lasers for Remote Sensing

C. High average power ultrafast lasers

D. Optical damage and plasma studies with ultrafast lasers

High Average Power Diode Pumped Solid State Lasers

Power Scaling with high spectral and spatial coherence

Research Objectives: •to improve the efficiency of diode pumped solid state lasers such as in-band pumping, reduction of loss in the laser materials, improved pumped efficiency, and operation of phased array spatial mode lasers.

•to scale the average power while maintaining coherence by extending the master oscillator, power amplifier approach to encompass cw, energy storage, and ultrafast pulse format operation.