Overview of high power THz sources from laser-plasma interaction

Transcription

1 Lecture at the 5th ASS&S SIOM-CAS, Shanghai August 16-20, 2010 Overview of high power THz sources from laser-plasma interaction Z.M. Sheng Department of Physics, Shanghai Jiao Tong University / Institute of Physics, CAS

2 Outline What to do with intense THz sources Intense THz sources with electron bunches Power THz sources from laser plasmas-experiments Power THz sources from laser from laser wakefield by linear mode from a thin plasma layer by transient of emission from laser by residual transverse currents from field of external DC/AC fields applied to plasma Summary

3 What is THz radiation? Molecular rotations, Collisions between gas phase molecules, Electron response in semiconductors and their nanostructures, Superconducting energy gaps, Collective modes of proteins vibration,.. G. Williams, Rep. Prog. Phys.69, 301 (2006)

4 Applications of Strong THz fields THz pump experiments THz pumping of metals, insulators, and correlated electron materials. Coherent band-gap distortion & phase transition. THz-pump optical-probe experiments. THz coherent control Rapid THz imaging Biomedical and security imaging Strong THz sources Photo courtesy: the Star Tiger E THz > 1 MV/cm Nonlinear THz Optics THz 2nd, 3rd nonlinear effects. Extreme nonlinearity with ponderomotive energy > photon energy THz-optical nonlinear mixing High magnetic field effects 1 MV/cm 0.3 T Pulsed electron spin resonance THz spintronics * M. S. Sherwin et al., DOE-NSF-NIH Workshop on Opportunities in THz Science

5 Courtesy of X.J. Wang

6 Nonlinear optics: Time-dependent Cross Phase Modulation (XPM) Y. Shen et al.,prl, 99: (2007); Y. Shen et al. PRA, 78, (2008).

7 Courtesy of X.J. Wang

8 Outline Why to do with intense THz sources Intense THz sources from electron bunches Power THz sources from laser plasmas-experiments Power THz sources from laser from laser wakefield by linear mode from a thin plasma layer by transient of emission from laser by residual transverse currents from field of external DC/AC fields applied to plasma Summary

9 Strong THz sources from large facilities FEL Linacs Synchrotrons Photo courtesy: DESY Photo courtesy: ALS Stanford, UCSB, FELIX SLAC, JLab,BNL ALS (BNL) Free electron lasing synchrotron radiation Coherent synchrotron radiation M. S. Sherwin et al., DOE-NSF-NIH Workshop on Opportunities in THz Science

10 THz Free electron lasers From Opportunities in THz Science, Report of a DOE-NSF-NIH Workshop held February 12 14, 2004, Arlington, VA, Ed. by M. S. Sherwin et al.

11 THz generation from ultrashort electron bunches coherent Incoherent G. L. Carr et al., Nature 420, 153 (2002). M. Abo-Bakr et al., PRL 90, (2003)

12 Courtesy of X.J. Wang

13 THz radiation source at the Compact ERL (energy recovery linac) Terahertz coherent synchrotron radiation K. Harada et al. / Infrared Physics & Technology 51 (2008)

14 THz from laser-plasma produced ultrashort electron bunches Jeroen van Tilborg, PhD Thesis, 2006 Phys. Rev. Lett. 96(1), (2006)

15 Outline Why to do with intense THz sources Intense THz sources with electron bunches Power THz sources from laser plasmas-experiments Power THz sources from laser from laser wakefield by linear mode from a thin plasma layer by transient by residual transverse currents from field of external DC/AC fields applied to plasma Summary

16 Different plasma-based THz generation techniques M. D. Thomson, M. Kress et al., Laser & Photon. Rev. 1, No. 4, (2007)

17 THz emission associated with laser driven plasma oscillations H. Hamster et al., Phys. Rev. Lett. 71, 2725 (1993); Phys. Rev. E 49, 671 (1994).

18 THz emission from laser-driven filaments in air G. Mechain et al., Appl. Phys. B 77, 707 (2003); S. Tzortzakis et al., Opt. Lett. 27, 1944 (2002);

19 Conical Forward THz Emission from Femtosecond- Laser-Beam Filamentation in Air Transition-Cherenkov emission from the plasma space charge moving behind the ionization front at light velocity. C. D Amico et al., PRL 98, (2007).

20 Efficient way of THz generation D. J. Cook and R. M. Hochstrasser, "Intense terahertz pulses by four-wave rectification in air," Opt. Lett. 25, (2000) w+2w THz Xu Xie, J. Dai, and X.-C. Zhang, PRL 96, (2006)

21 THz emission from a dc-biased laser filaments in air Yanping Chen et al., APL 95, (2009)

22 Pyroelectric signal (a.u.) Super-broad THz spectrum in laser-gas interaction Spectral power (norm.) Spectral power (norm.) Spectral power (norm.) 1000 Fourier-transform spectra THz energy vs pressure Kr Ar 10 torr Ar N Ar 100 torr 400 Air He Air 580 torr Pressure (torr) E THz ~ 5 J/pulse with Kr (C.E. > 10-4 ) Frequency (THz) K. Y. Kim et al., Nature Photonics doi: (2008).

23 THz Radiation from Cerenkov wake in a magnetized plasma B plasm a w/k, w ~ w p Laser pulse v g N. Yugami et al., Phys. Rev. Lett. 89, (2002). N. Spence et al., Phys. Plasmas 8, 4995 (2001).

24 THz emission associated with ultrashort electron bunches: transition radiation Plasma E-Beam Transition radiation W. P. Leemans et al., Phys. Rev. Lett. 91, (2003); E. Esarey et al., Phys. Rev. E 69, (2004); J. van Tilborg, et al., Phys. Rev. Lett. 96(1), (2006)

25 Outline Why to do with intense THz sources Intense THz sources with electron bunches Power THz sources from laser plasmas-experiments Power THz sources from laser from laser wakefield by linear mode from a thin plasma layer by transient of emission from laser by residual transverse currents from field of external DC/AC fields applied to plasma Summary

26 Recent experimental results on laser wakefield acceleration: 1GeV in 3cm! W. Leemans et al., Nature Physics (2007)

27 An electron plasma wave is potentially a coherent high-power THz source Plasma waves that can be driven by ultrashort laser pulses oscillate typically at the THz range (e.g., n e =10 18 cm -3, w p /2p=9THz). The field strength before wave-breaking is as high as GV/cm for n e =10 18 cm -3. For example, LBL 1GeV in ~cm. How can an electrostatic wave (E//k) be converted to an electromagnetic wave? (Usually env is cancelled by -de/dt )

28 Dispersion of electromagnetic waves and electron plasma waves EM wave w Slope c w k c + ES wave w 2 pe w pe Langmuir waves Slope 3 1/2 v te 2 3k 2 v 2 w 2 e pe w + kl De They meet each other only at k=0. 1

29 THz radiations from a vacuum-plasma interface by introducing an inhomogeneous plasma region w ~2p/ L w w 2p / 2 p 16-3 p L 2 n mw / 4pe 2 L w pe 1THz, n e cm ZM Sheng et al., Phys. Rev. E 69, (R) (2004). ZM Sheng et al., Phys. Rev. Lett. 94, (2005). ZM Sheng et al., Phys. Plasmas.12, (2005). HC Wu, ZM Sheng et al., Phys. Rev. E, 75 (2007),

30 Wave vector of a plasma wave in inhomogeneous plasmas 3 / ), (, ) / ( ), / ( / t v x for k x t v x t x k L x L x n n g p g p p - w w w g p g p p v x t Since k x L x t v x L t x k L x L x n n / 0 ) 2( ) ( ) 2( ), (, ) / (1 ), / ( / w w w

31 Wakefield driven by ultrashort laser pulses: longitudinal electric field (a=0.5, T=20, n/l=0.01n c /60l)

32 A key aspect: evolution of the wave vector ( x, t) w ( x )( t -x / v ), 0 p 0 0 k / x k 0 0 g

33 Linear model conversion ES Resonance absorption q EM n c cos 2 q n c EM ES

34 Energy conversion efficiency scaling C mainly depends upon the incident angle and the pulse profile. d L L n ~ ~ w w l l l L a a n n L d C c L energy

35 Coherent Wake Emission e-

36 Conical emission for normal incidence of a laser pulse with a finite beam diameter (a=0.5, T=20, n/l=0.01n c /60l)

37 Effect of transverse beam size W=10l, t150 W=20l, t150

38 Two-dimensional simulation of oblique incidence W=10l, q15 o, t160 W=20l, q15 o, t160

39 Outline Why to do with intense THz sources Intense THz sources with electron bunches Power THz sources from laser plasmas-experiments Power THz sources from laser from laser wakefield by linear mode from a thin plasma layer by transient of emission from laser by residual transverse currents from field of external DC/AC fields applied to plasma Summary

40 Single-Cycle emission from thin plasma layers H. C. Wu, Z. M. Sheng et al., Phys. Rev. E 77, (2008). Mechanisms: net transient currents at the vacuum-plasma boundaries.

41 Scaling with the laser intensity and incident angle The THz field amplitude 1/ 2 2 L e n a sinq T 0

42 Weakly relativistic theory model If an electron bunches interacting with a solid target, there appears similar effects. q n e a n 2 / 1/ 2 0 e 1/ 2 2 e n v n a e 0 sin q

43 Single cycle emission from steep plasma density profiles When w p >2p/ L d L =c L, k L =2p/d L XG Dong et al., PRE 2009

44 Outline Why can one do with intense THz sources Intense THz sources with electron bunches Power THz sources from laser plasmas-experiments Power THz sources from laser from laser wakefield by linear mode from a thin plasma layer by transient of emission from laser by residual transverse currents from field of external DC/AC fields applied to plasma Summary

45 P. Sprangle et al., Phys. Rev. E 69, (2004). A model for emission from laser filamens

46 a n 2 / 1/ 2 0 e B r n 1/ 2 e a 2 0

47 Why It is emitted in single cycle H.C. Wu, et al., submitted (2009) Second harmonic

48 Outline Why to do with intense THz sources Intense THz sources with electron bunches Power THz sources from laser plasmas-experiments Power THz sources from laser from laser wakefield by linear mode from a thin plasma layer by transient of emission from laser by residual transverse currents from field of external DC/AC fields applied to plasma Summary

49 THz emission from residual currents Residual transverse currents Ways to increase the residual currents: With two pulses With a chirped pulse With a few cycle pulse

50 A three-step model for THz emission from field ionization 1. Electrons are freed from atoms by the tunneling ionization. 2. Free electrons get transverse momenta while the laser pulse passes by. 3. All moving electrons form an oscillating electric dipole, which emits THz waves. H.C. Wu, J. Meyer-ter-Vehn, Z.M. Sheng, New J. Phys. 10, (2008).

51 THz emission in relevance with the CEP These THz emissions are sensitive to the relative phase of the two color waves or the absolute phase or carrier envelope phase (CEP) of the few-cycle pulse. Dj [1] D. J. Cook and R. M. Hochstrasser, Opt. Lett. 25, 1210 (2000). [2] M. Kress et al., Opt. Lett. 29, 1120 (2004). [5] M. Kress et al., Nat. Phys. 2, 327 (2006).

52 PIC simulation for linearly-polarized light 90 degree Circularly polarized light produces linearly polarized THz emission.

53 Simulation with two-color lasers a 1 =0.06

54 THz field scaling for the two-color laser scheme

55 THz field scaling with chirped laser pulses A Chirped pulse v ~ a 0 W. M. Wang, Z. M. Sheng et al., Opt. Express 16, (2008).

56 Outline Why to do with intense THz sources Intense THz sources with electron bunches Power THz sources from laser plasmas-experiments Power THz sources from laser from laser wakefield by linear mode from a thin plasma layer by transient of emission from laser by residual transverse currents from field of external DC/AC fields applied to plasma Summary

57 Emission by external DC/AC fields applied to plasma +V W.M. Wang et al., J. Appl. Phys. 107, (2010)

58 Numerical simulation

59 Emitted field scales linearly with the applied field

60 L Relation with plasma scalelength

61 Relation with plasma sizes T=167fs T=400fs

62 Summary Laser-plasma can be an efficient intense THz source Most experiments performed can be explained by existing theories. High power radiation in the THz range by driving high amplitude EPW: mode conversion High conversion efficiency, MW in the power. Single cycle MW THz pulses with a gas jet in a diameter. The mechanism is the transient net currents generation. Residual currents from field ionization responsible for the THz emission found in laser-gas interaction. A biased field tends to increase the currents and thus increase the emission amplitude. With a chirped pulse or few cycle pulse, the residual currents can be increased significantly to produce a high amplitude THz wave.

63 Acknowledgements H. C. Wu, M. Chen, W. M. Wang, X.G. Dong, H. W. Du, C. Li, Y. T. Li, J. Zhang Institute of Physics, CAS and Dept. Phys., Shanghai Jiao Tong Univ. Thank you for your attention!