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Institute of Atomic and Molecular Sciences, Academia Sinica, Taiwan

Production of intense ultrashort mid-infrared pulses from a laser-wakefield electron accelerator. Chih-Hao Pai , Li-Chung Ha, Yen-Mu Chen, Hsu-Hsin Chu, Jiunn-Yuan Lin, Jyhpyng Wang, Szu-yuan Chen. Institute of Atomic and Molecular Sciences, Academia Sinica, Taiwan

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Institute of Atomic and Molecular Sciences, Academia Sinica, Taiwan

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  1. Production of intense ultrashort mid-infrared pulses from a laser-wakefield electron accelerator Chih-Hao Pai, Li-Chung Ha, Yen-Mu Chen, Hsu-Hsin Chu, Jiunn-Yuan Lin, Jyhpyng Wang, Szu-yuan Chen Institute of Atomic and Molecular Sciences, Academia Sinica, Taiwan National Taiwan University, Taiwan National Central University, Taiwan National Chung Cheng University, Taiwan

  2. Outline • Methods for the generation of sub-ps mid-infrared pulses • Laser-wakefield electron accelerator operated in the bubble regime • Experimental setup and tomographicmeasurement • Generation of intense ultrashort mid-infrared pulses in the bubble regime

  3. Generation of sub-ps MIR pulses • Free-electron lasers: • Frequency conversion in nonlinear crystals or gas media: [1] Fuji et al., Opt. Lett. 32, 3330 (2007) [2] Imahoko et al., Appl. Phys. B 87, 629 (2007) • This work:

  4. Laser-wakefield electron accelerator operated in the bubble regime Pukov et al., Appl. Phys.B74, 355 (2002)

  5. Laser-wakefield electron accelerator operated in the bubble regime monoenergetic electron beam energy: 50 MeV±10％, divergene: 4 mrad duration: ~10 fs (PIC simualtion) 200 mJ, 42 fs 4x1019 cm-3 plasma density Phys.Rev. E75, 036402 (2007) Pukov et al., Appl. Phys.B74, 355 (2002)

  6. Laser-wakefield electron accelerator operated in the bubble regime spectral broadening Faure et al., Phys. Rev. Lett.95, 205003 (2005)

  7. Experimental setup for production of electron beam • Diagnostic tools • LANEX imaging system for electron beam • Interferometry for plasma density measurement SLM: spatial light modulator OAP: off-axis parabolic mirror

  8. Diagnoses for MIR pulse (1): spectrometer • Diagnostic tools • LANEX imaging system for electron beam (replaced by (c)) • Interferometry for plasma density measurement • (c) MIR grating spectrometer SLM: spatial light modulator OAP: off-axis parabolic mirror

  9. Diagnoses for MIR pulse (2): energy & beam profile • Diagnostic tools • LANEX imaging system for electron beam (replaced by (d)) • Interferometry for plasma density measurement • (c) MIR grating spectrometer • Pyroelectric detector SLM: spatial light modulator OAP: off-axis parabolic mirror

  10. Diagnoses for MIR pulse (3): temporal profile • Diagnostic tools • LANEX imaging system for electron beam (replaced by (e)) • Interferometry for plasma density measurement • (c) MIR grating spectrometer • Pyroelectric detector • Ge-wafer photo-switch SLM: spatial light modulator OAP: off-axis parabolic mirror

  11. Scanning the interaction length for tomographic measurement intensity of the machining pulse Phys. Plasmas 12, 070707 (2005) Phys. Rev. Lett. 96, 095001 (2006) • The machining beam ionizes and heats up selected regions. • Plasma heating leads to hydrodynamic expansion. • Several nanoseconds later the ionized region is evacuated. • Characteristics of final products as functions of pump-pulse • positions in the gas jet can be measured.

  12. Setup of the machining beam for tomographic measurement function of the knife-edge:setting the interaction length pump pulse focal spot: 20 m1.3 mm variable position knife-edge or SLM cylindrical lens pair gas jet machining pulse

  13. Dependence of MIR energy on interaction length self-injection regions of electrons pump pulse energy: 205 mJ pump pulse duration: 42 fs plasma density: 4.1x1019 cm-3 Self-injection of the monoenergetic electron beam and rapid growth of the MIR pulse occurs in the same region.

  14. 0 Dependence of MIR spectra on interaction length pump pulse energy: 205 mJ pump pulse duration: 42 fs plasma density: 4.1x1019 cm-3 The spectral profile of the MIR pulse suggests that the MIR pulse is produced by the strong spectral broadening of the pump pulse in the bubble regime.

  15. 0 Dependence of MIR spectra on interaction length The Raman satellite is related to the modulational instability of the pump pulse in the early stage of the bubble regime evolution. The spectral profile of the MIR pulse suggests that the MIR pulse is produced by the strong spectral broadening of the pump pulse in the bubble regime.

  16. Dependence of MIR energy on plasma density pump pulse energy: 205 mJ pump pulse duration: 42 fs The MIR pulse energy increases with plasma density faster than the emergence of the monoenergetic electron beam. This is consistent with the bubble-regime model as the strong spectral broadening and self-compression is the cause of bubble formation.

  17. Dependence of MIR energy on pump energy plasma density: 4.1x1019 cm-3 The MIR pulse has a lower pump energy threshold than that of the monoenergetic electron beam. This is consistent with the bubble-regime model as the strong spectral broadening and self-compression is the cause of bubble formation.

  18. Polarization of the MIR pulse The data rule out the possibility of other mechanisms • coherent transition radiation from the electron bunch passing the plasma-vacuum boundary • (2) Cherenkov-type emission from the electron bunch or the plasma wave • Both are radially polarized. polarization axis of the pump pulse Ref: Leemans et al., Phys. Rev. Lett. 91, 074802 (2003) The MIR pulse is linearly polarized with the same polarization as the pump pulse. This is consistent with the bubble-regime model since the spectral broadening by phase modulation should preserve the pump laser polarization.

  19. MIR pulse energy vs. iris radius radius of the ZnSe vacuum window pump pulse energy: 205 mJ pump pulse duration: 42 fs plasma density: 4.1x1019 cm-3 The MIR pulse is a flattop distribution with its diameter determined by the clear aperture of the ZnSe vacuum window. The angular divergence of the MIR pulse is larger than the collection angle (8°) and the total MIR pulse energy should be considerably larger than 3 mJ.

  20. Ge-wafer photo-switch excitation pulse MIR pulse pinhole

  21. Ge-wafer photo-switch excitation pulse MIR pulse pinhole

  22. Ge-wafer photo-switch excitation pulse MIR pulse pinhole

  23. Temporal profile of the MIR pulse temporal profile Ge-wafer photo-switch pump pulse: 205 mJ/42 fs excitation pulse: 500 mJ/38 fs plasma density: 4.1x1019 cm-3 5-mm Ge window 5-mm Ge window pulse duration X ps 4.6 ps 9.8 ps X＜0.6 ps

  24. Summary Production of an intense MIR pulse with at least 3-mJ pulse energy and ultrashort pulse duration from a laser-wakefield electron accelerator is demonstrated. The output energy is one order of magnitude larger than that of the most intense free electron lasers, and three order of magnitude larger than that of conventional wave mixing. Experimental data suggest that the MIR pulse is produced by the strong spectral broadening of the pump pulse in a laser- wakefield electron accelerator operated in the bubble regime.

  25. Thanks for your attention.

  26. Picture of experimental chamber

  27. Picture of experimental chamber machining beam main beam (1) MIR (2) electron beam

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