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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.
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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
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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
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Fabrication of transient plasma waveguides
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interaction region tight focusingshort interaction length Limitation of interaction length
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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
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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
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High brightness EUV lasers Opt. Lett. 34, 3562 (2009) Phys. Rev. Lett. 99, 063904 (2007) Appl. Phys. B 105, s00340 (2011)
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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
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Energy levels of EUV lasers
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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
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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
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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
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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
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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
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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)
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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%
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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
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Accelerating electrons in a transient plasma waveguide Physics of Plasmas 18, 063102 (2011)
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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
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Electron acceleration in plasma waveguide Phys. Plasmas 18, 063102 (2011) beam profile at exit (~12 m FWHM). density profile of the waveguide
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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
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Generating few-cycle intense mid- infrared pulses Phys. Rev. A 82, 063804 (2010)
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Nonlinear phase modulation in the bubble regime density modulation relativistic self-phase modulation modulation of refractive index laser field electron density
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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)
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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)
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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)
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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)
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Thank you for your attention!
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