1. Ultrafast particle and photon sources driven by intense laser ‐ plasma interaction Jyhpyng Wang Institute of Atomic and Molecular Sciences, Academia Sinica Dept. of Physics, National Taiwan Univ. Dept. of Physics, National Central Univ.

2. Core members of experimental team Prof. Szu-yuan Chen, Academia Sinica Prof. Jiunn-Yuan Lin, Nat’l Chung-Cheng Univ. Prof. Hsu-Hsin Chu, Nat’l Central Univ. Computer Simulation Prof. Shih-Hung Chen, Nat’l Central Univ. Theoretical Analysis Prof. Gin-yih Tsaur, Tunghai Univ. Collaborators

3. Fabrication of transient plasma waveguides High brightness extreme-UV lasers Accelerating electrons in a transient plasma waveguide Generating few-cycle intense mid-infrared pulses Outline

4. Fabrication of transient plasma waveguides

5. interaction region tight focusingshort interaction length Limitation of interaction length

6. creating seed electrons heating up and generating more electrons shock expansion & collisional ionization forming a plasma waveguide Plasma-waveguide formation from a line focus Phys. Plasmas 11, L21 (2004) heater ignitor axicon line focus ignitor heater

7. length > 1.2 cm ignitor: 15 mJ, 55 fs heater: 85 mJ, 80 ps (1.1 ns delay) probe: 1.2 ns after heater density variation < 20% electron density profile Phys. of Plasma 11, L21 (2004) Laser-drilled plasma waveguide

8. High brightness EUV lasers Opt. Lett. 34, 3562 (2009) Phys. Rev. Lett. 99, 063904 (2007) Appl. Phys. B 105, s00340 (2011)

9. 2p 3p 3s Ne-like ions: Ar 8+, Ti 12+, Fe 16+ collisional excitation (~200 eV) fast relaxation lasing lifetime = ~3 ps Energy levels of EUV lasers He-Ne laser

10. Energy levels of EUV lasers

11. multiphoton ionization tunneling ionization above-threshold ionization Optical-field ionization appearance intensity for 1 + ion ( =1  m) Xe: 8.7  10 13 W/cm 2 He: 1.5  10 15 W/cm 2 above-threshold ionization heating

12. Energy levels of the Ni-like Kr laser Using a high-intensity pulse to ionize Kr atoms to a closed shell (Kr 8+ ) Electrons gain energy from the pump pulse and excite the ions by collision

13. pump pulse nozzle Longitudinally pumped optical-field-ionization EUV lasers gas jet defocusing quickly reduces intensity pump pulse lower refractive index higher refractive index advantages: high efficiency excellent beam profile no debris problem: ionization defocusing

14. Interferograms of the plasma waveguide pump pulse: 45 fs, 235 mJ ignitor: 45 fs, 45 mJ heater: 80 ps, 225 mJ ignitor-heater separation: 200 ps hearer-pump delay: 2.5 ns atom density: 1.6×10 19 cm -3 electron density distribution A uniform plasma waveguide of 40-  m diameter and 9-mm length is produced with the axicon-ignitor-heater scheme. The guided beam size is ~15  m (FWHM). (1) (2) (1) (2) after fabrication after guided pulse passing

15. without waveguide pump pulse: 45 fs, 235 mJ focal position: 2.75 mm pump polarization: circular pure Kr waveguide pump pulse: 45 fs, 235 mJ pump polarization: circular focal position: 500  m ignitor: 45 fs, 45 mJ heater: 80 ps, 225 mJ ignitor-heater separation: 200 ps heater-pump delay: 2.5 ns trade-off between larger gain coefficient and more severe ionization defocusing Phys. Rev. Lett. 99, 063904 (2007) 400-fold enhancement by using plasma waveguide Atom-density dependence for Ni-like Kr lasing at 32.8 nm

16. Experimental set-up for HHG injection seeding x-ray mirror parabolic mirror axicon bored lens parabolic mirror pump for high harmonic generation high harmonic seed x-ray laser pump Ar jet Kr jet amplified x-ray pulses for waveguide fabrication (ignitor & heater) pulse timing diagram time Opt. Lett. 34, 3562 (2009)

17. Angular distribution of the seeded EUV laser gas: argon atom density: 7.1×10 18 cm -3 pump energy: 3.8 mJ pump duration: 360 fs focal position: 1250  m seed-amplifier pump delay: 2 ps gas: krypton atom density: 1.6×10 19 cm -3 pump pulse: 38 fs, 235 mJ ignitor: 38 fs, 45 mJ heater: 160 ps, 270 mJ ignitor-heater separation: 200 ps heater-pump delay: 2.5 ns parameters of HHG seed: parameters of x-ray amplifier: beam-pointing fluctuation: 0.13 mrad With seeding the divergence of the x-ray laser is greatly reduced from 4.5 mrad to 1.1 mrad, which is about the same as that of the HHG seed. With the waveguide-based soft-x-ray amplifier, the HHG seed is amplified by a factor of 10 4. unseeded laser seeded laser high harmonic seed energy fluctuation: 10%

18. Output of 32.8-nm Ni-like Kr laser 6  J/pulse pumped by the 100-TW laser at Nat’l Central Univ pumped by the 10-TW laser at Academia Sinica 600 pump energy (mJ) Applied Physics B 105, s00340 (2011) efficiency = 10 -5

19. Accelerating electrons in a transient plasma waveguide Physics of Plasmas 18, 063102 (2011)

20. Electron acceleration in the “bubble regime” After nonlinear propagation, the laser pulse becomes spatially self- focused and temporally compressed. The ponderomotive force expels electrons, resulting in a positively charged cavity following the laser pulse. laser field electron density

21. Electron acceleration in plasma waveguide Phys. Plasmas 18, 063102 (2011) beam profile at exit (~12  m FWHM). density profile of the waveguide

22. electron energy: 300 MeV pump pulse: 1.3 J bunch charge: 200 pC (best case) divergence: 2.5 mrad ∆E/E: 13% Phys. Plasmas 18, 063102 (2011) Issues: beam pointing stability, bunch charge stability Electron beam profile and energy spectrum

23. Generating few-cycle intense mid- infrared pulses Phys. Rev. A 82, 063804 (2010)

24. Nonlinear phase modulation in the bubble regime density modulation relativistic self-phase modulation modulation of refractive index laser field electron density

25. Ge-wafer photo-switch mid-IR pulse excitation pulse pinhole mid-IR pulse A. J. Alcock and P. B. Corkum, Can. J. Phys. 57, 1280 (1979)

26. Ge-wafer photo-switch mid-IR pulse excitation pulse pinhole mid-IR pulse A. J. Alcock and P. B. Corkum, Can. J. Phys. 57, 1280 (1979)

27. Temporal profile of the mid-IR pulse photo-switch gated transmission pump pulse: 205 mJ/42 fs excitation pulse: 500  J/38 fs plasma density: 4.1x10 19 cm -3 reconstructed temporal profile pulse duration X 4.6 ps 9.8 ps 5-mm Ge window X ～ 15 fs mid-IR energy (arb. units) intensity (arb. units) consistent with particle-in-cell simulation delay of excitation pulse with respect to mid-IR pulse (ps)

28. Comparing with simulation and theoretical estimation Simulation: mid-IR peak power in the bubble: > 0.5 TW Square of the electric field of the numerically filtered mid-IR pulse The mid-IR pulse is encapsulated in the low-density bubble, hence is not absorbed by the plasma. The wavelength-scale bubble ensures high spatial coherence. 2 － 20  m 6 － 10  m 2 － 6  m 10 － 20  m Estimation based on Fourier transform of the phase modulated pulse Measured energy: 3 mJ (conversion efficiency=1.5%) Phys. Rev. A 82, 063804 (2010)

29. Thank you for your attention!