Room-temperature Burst-mode GHz and THz Pulse Rate Photoinjector for Future Light Sources Yen-Chieh Huang * Chia-Hsiang Chen, Kuan-Yan Huang, Fu-Han Chao HOPE Laboratory, Institute of Photonics Technologies National Tsinghua University (NTHU), Hsinchu, Taiwan AFAD 2014 and ACAS Workshop on Future Light Sources, Jan , 2014 (2E-33)

OUTLINE 1.Motivations – high average power, electron bunching 2.Burst-mode GHz photoinjector  high- average power FEL 3.Burst-mode THz photoinjector  superradiant THz FEL 4.Dielectric Laser Accelerator  Mini-XFEL 5.Conclusions

photoinjector velocity bunching IDEA GHz ~ THz Bunching Frequency Multiplication macropulse Compressed macropulse Magnetic bunching PHz

Burst-mode GHz Photoinjector RF pulse Electron micro-pulse ~s~s ms Hz > kHz 300 mJ 532 nm Multi-pass amplifier 3 rd -harmonic generator photoinjector High average power FEL/FELO 3.5 ns Pulse Picker PC Ti:sapphire Seed GHz (Gigaoptics) GHz gun driver laser

Burst-mode THz Photoinjector Pulsed laser beat wave at 1.56  m CW, low-power seed laser at 1.56  m combined from two diode lasers beating at THz frequencies Ti:sapphire laser amplifier + THG UV laser beat wave at 260 nm Mode-locked pump at 1064 nm OPA Optical Parametric Amplifier Second harmonic generator Pulsed laser beat wave at 780 nm SHG

pump Dichroic mirror Seed signal signal pump idler Comb-spectrum OPA  p0 signal f idler pump f f t Initial beat wave t Final short pulse train (Y. C. Huang et al., CLEO (CWC3), San Jose, USA, May 7, 2008 ) Harmonic generator photocathode Optical parametric amplifier

1064 nm pumped two-color OPA (1064-nm pumped OPA, s = ~1.55  m, i = ~3.3  m) EDFA Telecom diode 1539 nm, 1545 nm Narrow-line wavelength-tunable laser (ECDL) DFB laser ECDL DFB ECDL Pulsed pump at 1064 nm PPLN OPA Pump Signal Amplified seed signal Self-modulated sidebands 3 THz 0.75 THz Crystal length = 4 cm or 45 l g s-p GVM = 1 ps/cm i-p GVM ~ 0 PPLN  = 29.6  m (~ 15 THz tuning range!)

9 Photocathode gun Solenoid 50~100 cm Single-pass undulator 50 cm 12 cm THz-pulse-train laser 10 MW power at THz Desktop MW THz Free-electron Laser Yen-Chieh Huang, “Desktop MW Superradiant Free-electron Laser at THz Frequencies,” Applied Physics Letters, 96, (2010) *Photocathode gun – courtesy of CX Tang of Beijing Tsinghua U and NSRRC

10 20% linear taper > 14 MW Tapered undulator Maintaining

THz-pulse-train laser 10 MW power at THz Photocathode gun Solenoid 50~100 cm Single-pass undulator 50 cm 12 cm Nrrow line THz THz DFG Narrow-line mW THz wave (Nonlinear material) EDFA Narrow-line wavelength-tunable laser (ECDL) DFB laser ECDL DFB ECDL PPLN OPA PPLN (~ 15 THz tuning range!) Pulsed 1064 nm PPLN THz DFG 4K Si bolometer wavelength (  m) THz-wave power (a.u.) wavelength (  m) ~1.5 THz 0.6 THz (Poster)

Would the nano-bunches survive during acceleration and propagation (radial acc. and space-charge forces)?

Adaptive optics available for laser pulse- front shaping

Dielectric laser accelerator (DLA) Dielectric Laser Accelerator 1.Solid state  stable 2.Dielectric damage field and thus high acceleration gradient (up to 1-10 GeV/m) 3.Fabrication compatible to semiconductor lithographic patterning technique Huang & Byer (1996)

300 MeV/m

Dielectric Laser Accelerator (DLA)  -bunch length (0.1~1% ) M-pulse length bunch charge energy spread norm. emittance peak current M-pulse rate 1-10 nm or 3.3~33 as ~100 fs10 fC ~ 1 pC ~0.1%10  9 ~10  11 m-rad 0.3~20 kA ~ MHz 300 THz

Quantum FEL Con: (1) 1 photon from 1 electron  low efficiency (2) Electron recoil induced energy spread << FEL gain bandwidth Define quantum  parameter Classic regime (  large enough) Quantum regime Pro: quantum noise added to startup power P , usually small, could assist FEL buildup. Virtual photon (unndulator) To stay in the gain bandwidth FEL gain bandwidth ~  /  ~ 

Dielectric Laser Undulators ( u >> laser to operate with large  ) T. Plettner, R. L. Byer, Phys. Rev. ST Accel. Beams 11, (2008). Electron velocity Laser phase velocity G. Travish and R. B. Yoder, Proceedings SPIE 8079, (2011). for E laser ~ 1 GV/m

Quantum regime Straight lines are gain-length contours in mm DLA-driven soft-x-ray FEL (laser undulator B u ~ 3 T, r = 1 nm) 50 MeV line u = 20  m Peak current = 5 kA, gain length = 1 mm,  ~ Assume rms beam radius = 100 nm To be published in Review of Modern Physics

Straight lines are gain-length contours in mm DLA-driven hard-x-ray FEL (laser undulator B u ~ 3 T, r = 1 Å) u = 100  m Quantum regime 300 MeV line Peak current ~ 12 kA, gain length ~ 3 mm Assume rms beam radius = 100 nm gamma

Conclusions 1.GHz burst-mode photoinjector: it is a matter of developing a GHz burst mode laser amplifier THz burst-mode photoinjector: it is a matter of developing a THz-modulated driver laser THz burst-mode accelerator: it is matter of developing a dielectric laser accelerator THANK YOU FOR YOUR ATTENTION 4. High rep rate allows high average power, short bunches help buildup of XFEL