Laser Acceleration Experiments at ORION

1. 2nd ORION Workshop February 18-20, 2003 Laser Acceleration Experimentsat ORION Professor Robert L. Byer Stanford University Dept. Applied Physics

2. 2nd ORION Workshop February 18-20, 2003 Outline The Promise of Laser Acceleration Recent Progress in Lasers Recent Laser Acceleration Mechanisms Low Field (ao<<1) Acceleration and High Field (ao1) Experiments in Laser Acceleration Future Issues

3. The Promise of Laser Acceleration 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 [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).

4. 30cm 3cm 3mm 300m 30m 3m300nm High Gradient Requires High Energy Density Pf 2 E. Colby Source Wavelength *28.5 GeV, 1e10 ppp, 1m x 1m x 600m (20m for SPPS) beam **350 MeV, 1e10 ppp, 1m x 1m x 1 mm beam

5. High average power ultra-fast lasers Existing widespread commercial ultra-fast laser systems: Ti:sapphire Poor optical efficiency  poor wall-plug efficiency Low saturation  low power systems (typically few Watts per laser) Large scale multi-component systems that require water cooling High costs systems (~100 k$/laser of ~1Watt avg. power) Requirements for future ultra-fast lasers for particle accelerators • Power scalability to hundreds for Watts of average power per laser • Wall-plug efficiency > 20% • Mass producible, reliable and low-cost • Ultra low optical phase noise Driving Applications Industry and Basic Research Materials Processing, ultrafast laser machining, via drilling, medical therapeutics, entertainment, image recording, remote sensing Defense Coherent laser radar, remote wind sensing, remote sensing of “smart dust”, trans-canopy ranging, and stand-off coherent laser inspection of laminated-composite aircraft components

6. Candidate laser host materials for ultra-fast high-power lasers Monocrystalline materials Materials with low quantum defect, excellent slope efficiency, and good thermal conductivity 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) Polycrystalline materials Nd:YAG Nd: Y2O3 • Better homogeneity of dopant • Lower fabrication cost • Possible tailoring of dn/dT • Single crystal growth still possible Cr2+:ZnSe Nd:Y3ScxAl(5-x)O12

7. Commercially Available High Efficiency Laser Diode Bars 3900 W, he=40%, l=792-812 nm 300W, he=50%, l=780-1000 nm

8. Electrical Efficiency of Lasers Yb:KY(WO4)2 l=1.028m hslope=86.9% he=43% Gt=240 fsec Pave=22.0 W Opt. Lett., 27 (13), p.1162, July (2002). SLAC PPM Klystron l=2.624 cm Gt=3 msec Pave=27 kW h=65% Yb:KY(WO4)2 Yb:KGd(WO4)2 Yb:YAG Source Electrical Efficiency [%] Yb:Sr5(PO4)3F TUBES FELs LASERS (RF Compression, modulator losses not included) Yb:KGd(WO4)2 l=1.023m hslope=82.7% he=41% Gt=176 fsec Pave=1.1 W Opt. Lett., 25 (15), p.1119, August (2000). Cr++:ZnSe Er Fiber CO2 E. Colby Ti:Al2O3 Source Frequency [GHz]

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

10. Photonics Trend: Custom Optical Media b a • 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 c d 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.

11. 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 (l/200) RMS by 2010 (’01 ITRS) Demonstration of recent progress in lithography

12. Semiconductor and Advanced Opto-electronics Material Capabilities at Stanford • 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 receivers Diode pumped Laser Amplfier Studies Quantum Noise of solid state laser amplifiers Adaptive Optics for Laser Amplifier beam control Thermal Modeling of Diode Pumped Nd:YAG lasers Laser Interferometry for Gravity Wave detectionSagnac Interferometer for Gravitational Wave Detection Laser Inteferometer Isolation and Control Studies Interferometry for Gravitational Wave Detection Time and Frequency response characteristics of Fabry Perot Int. GALILEO research program: gravitational wave receivers Quasiphasematched Nonlinear DevicesQuasi Phasematched LiNbO3 for SHG of diode lasers, cw OPO studies in LiNbO3, and diffusion bonded, GaAs nonlinear materials

13. 2nd ORION Workshop February 18-20, 2003 Recent Progress and Proposals for Vacuum Laser Acceleration Experiments

14. Energy The Inverse Free Electron Laser STELLA (Staged Electron Laser Acceleration) experiment at the BNL ATF (STI Optronics/Brookhaven/Stanford/U. Washington) Optically Accelerated Beam Energy Energy Optically Modulated Beam Incoming Beam W. Kimura, I. Ben-Zvi, in proc. of Adv. Accel. Conc. Conf., Santa Fe, NM, 2000.

15. Interferometric Acceleration (Inverse Transition Radiation Acceleration) Interaction Length : ~1000 l ~0.1 ZR x Slit Width ~10 l Slit Width ~10 l E1 E1x Crossing angle: q z E1z Electron beam E2z E2x Waist size: wo~100 l E2 E1x + E2x = 0 |E1z + E2z| > 0 no transverse deflection nonzero electric field in the direction of propagation Terminating Boundary Terminating Boundary The laser beams are polarized in the XZ plane, and are out of phase by p Gradient limited to 70 MeV/m for g [R. J. Noble, 2001].

16. Interferometric Accelerators(Inverse Transition Radiation) Laser Electron Acceleration Project at Stanford/SLAC TEM00 Linear polarization Gaussian pulses, l=0.8 mm (Ti:Sapphire) Laser Acceleration in Vacuum at Brookhaven-ATF TEM*01 Radial polarization Gaussian Pulses, l=10.6 mm (CO2) Electron beam T. Plettner, et al, “The LEAP Project”, DOE Review Slides, April 14, 2000. V. Yakimenko, et al, from ATF User’s Meeting, January 31, 2002.

17. Laser Accelerator Microstructures Stanford/SLAC, LEAPE163 (SLAC) Photonic waveguidesare the subject of intensive research, and can be designed to propagate only the accelerating mode. 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) P. Russell, “Holey fiber concept spawns optical-fiber renaissance”, Laser Focus World, Sept. 2002, p. 77-82. TIR Fused Silica at 1.06m TIR Silicon at 2.5m TIR Silicon at 1.06 m X. Lin, Phys. Rev. ST-AB, 4, 051301, (2001). Electron beams

18. ZnSe Lenses Multicell Linear Acceleration Experiments Inverse Cerenkov Acceleration in Waveguide(Unfolded Fabry-Perot Interferometer) A. Melissinos, R. Tikhoplav (U. Rochester, Fermilab) Multicell ITR Accelerator Y.-C. Huang, NTHU, Taiwan 0.2 ATM He TEM01* mode l=1.0 mm (Nd:YAG) Status: Structure has been fabricated with 80% power transmission measured. Nd:YAG drive laser is under construction at Fermilab now. Expected gain: 250 keV over 24cm. Y-C. Huang, et al, Nat’l Tsinghua University. Images from ATF User’s Meeting, January 31, 2002.

19. Active Medium(Cerenkov Amplifier in Overmoded Waveguide)L. Schächter, Technion, Israel LASER MEDIA: Nd:YAG Laser pump power Accelerated bunch Trigger bunch LASER MEDIA: Nd:YAG Laser pump power 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. • Phase synchronism places tight constraints on material nonlinearity, nonuniformity, and on the geometric tolerances

20. a=3, q=39o a=3, q=46o a=2, q=46o Combined Ponderomotive and Nonlinear Compton Scattering Ponderomotive Acceleration (Demonstrated)(CEA-Lemeil-Valenton) High Field Acceleration Mechanisms ao~300 G. Malka, E. Lefebvre, J. Miquel, Phys. Rev. Lett. 78, 3314 (1997). P. X. Wang, Y. K. Ho, et al, J. Appl. Phys. 91 (2) p. 856, (2002).

21. Ponderomotive Acceleration and Focussing Ponderomotive Scattering with Deflection field to aid beam extraction High Field Acceleration Mechanisms Bs ao~68 a0~5 G. Stupakov, M. Zolotorev, Phys Rev Lett 86 5274 (2001). Y. Salamin, C. Keitel, Phys Rev Lett 88 095005 (2002).

22. Prospects for Producing Relativistic Laser Fields • DPSS Ti:sapphire  l=0.8 mm • 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

23. Experiments in Laser Acceleration • Laser 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 (st~1 ps) with short (st~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 (wo20 mm) with small electron beams (sr 20 mm) • Transverse spot jitter and laser pointing jitters must be small • Precision (~1 mm) spot size and position measurement required near accelerator

24. 2nd ORION Workshop February 18-20, 2003 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-b 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?

25. 2nd ORION Workshop February 18-20, 2003 Laser Acceleration Working Group Redwood Room “C” Bob Byer, Yen-Chieh Huang, WG Leaders 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?

26. BACK-UP SLIDES

27. 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 b=(1/n)*dn/dT+a~0 (same article as above) • Lithographically Treatable Materials • Silicon (l>1500nm) Silica • Optical ceramics Nd:YAG

28. Laser Linear Collider pre-Concept … Laser Accelerator l=1-2 m, G~1 GeV/m Photonic Band Gap Fiber structures embedded in optical resonant rings Permanent Magnet Quads (B’~1 kT/m) CW Injector Warm rf gun Cold Preaccelerator Optical Buncher 433 MHz x 105 e-/macropulse (600 mpulse/macropulse) eN~10-11 m (but note Q/eN ~ 1 mm/nC) An Acceleration Unit Laser amplifier Optical resonator PBG accelerator structure Phase control … Optical Debuncher Final Focus I.P.

29. 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. • Stanford Research Program (DARPA) • High Average Power CW Lasers • High energy Yb:YAG lasers for Remote Sensing • High average power ultrafast lasers • Optical damage and plasma studies with ultrafast lasers