Pohang, 22 Aug. 2013 Introduction to intense laser-matter interaction Chul Min Kim Advanced Photonics Research Institute (APRI), Gwangju Institute of Science and Technology (GIST) & Center for Relativistic Laser Science (CoReLS), Institute for Basic Science (IBS)
Contents 1. Preliminary Basic parameters: a 0 and U p Laser intensity vs material response 2. Strong field physics (SFP) Characteristics Three-step model High harmonic generation and ultrafast spectroscopy Perspectives 3. Relativistic laser-plasma interaction (RLPI) Characteristics Single electron under a laser field Relativistic laser pulse propagation A few examples from APRI/CoReLS research activities Perspectives
a 0 represents the laser field Vector potential of a given power LP: A τ = A cos ωτ i CP: A τ = A 2 where τ = t z/c & k = cos ωτ i ± sin ωτ j i j Normalized vector potential a 0 a 0 = A A 0 where A 0 = m ec 2 a 0 = v os meω0 c = c ee e, a 1 v os c Preliminary: Basic parameters: a 0 and U p
I and a 0 Irradiance I I time averaged power area = S = c E B 4π I and a 0 a 0 = 0.855 2 I 18 λ μm where I 18 : irradiance in 10 18 W/cm 2 Ex.) a 0 = 1 & λ = 800 nm I = 2.14 10 18 W/cm 2 Preliminary: Basic parameters: a 0 and U p
U p represents the influence of the laser field on the electron Ponderomotive potential U p Def.) Kinetic Energy of an electron under an EM field Contributed by 1. Transverse oscillation a 0 2. 3. 2 Longitudinal oscillation (LP only) a 0 2 Longitudinal drift a 0 1 only (non-relativistic): U p = m e c 2 a 0 2 4 1 only (mildly relativistic): U p = m e c 2 1 + a 0 2 1+2+3 (strongly relativistic): U p = m e c 2 a 0 2 4 m e c 2 = 0.511 MeV 2 1 Preliminary: Basic parameters: a 0 and U p
Ponderomotive potential (λ~μm) Material response depends on laser intensity Material response levels & phenomena Quantum vacuum - pair creation, dielectric vacuum R p, UltraR e, nucleons - Direct p drive, radiation reactions, photonuclear processes R e, NonR p - HHG, self-focusing, transparency, self-steepening, laser wakefields, indirect p drive APRI/CoReLS NonR bound/free e - non-perturbative nonlinear optics: HHG / ATI / Modified from Tajima et al., Optik & Photonik, 2010 Preliminary: Laser intensity vs material response
Non-perturbative nonlinearity due to freeelectron states U p I p (ev) where I p ionization potential Laser field ~ atomic field involvement of free-electron states, leading to insensitive dependence on nonlinear orders sub-cycle response (structural change, ionization) For λ~μm 1. I 10 10 W/cm 2 : perturbative nonlinear optics 2. I 10 13 W/cm 2 : non-perturbative nonlinear optics 3. I 10 16 W/cm 2 : plasma optics To observe SFP phenomena, an ultrashort pulse duration ( O(λ)) is required not to be overshadowed by low-intensity phenomena. femtosecond lasers SFP: Characteristics
The basic concepts of SFP are given by the Corkum s three-step model Tunneling ionization Acceleration Recombination and high harmonic generation Above-threshold ionization Double ionization (rescattering) Corkum, Phys. Rev. Lett. 71, 1993 SFP: Three-step model
HHG can produce attosecond EUV pulses ħω X = I p + K. E. ( 3.17U p ) Odd harmonics only (d t = d(t + T 2 )) Time-frequency distribution J. Phys. B 39, 3199 (2006) Phys. Rev. A 72, 033817 (2005) SFP: HHG and ultrafast spectroscopy
HHG spectrum shows typical features of nonperturbative nonlinear optics Perturbative HHG Γ n σ n I n where σ n drops exponentially with n: sensitive dependence on the nonlinear order Ψ(bound) is localized? Non-perturbative HHG Plateau: insensitive dependence Ψ(free) is non-localized? Li, Phys. Rev. A 39, 5751 (1989) SFP: HHG and ultrafast spectroscopy
Strong HHG with a two-color field Phys. Rev. Lett. 94, 243901 (2005) 0.6 μj @ 21 nm Even and odd harmonics Selection and enhancement of shortpath contribution leading to strong HHG Phys. Rev. A 72, 033817 (2005) SFP: HHG and attophysics
HHG pulses can probe ultrafast ionization dynamics HH + IR Holography with de Broglie waves P 1s3p (t) (---) & N 2ω (t) ( ) reconstructed Phys. Rev. Lett. 108, 093001 (2012) SFP: HHG and attophysics
The basic elements of SFP are understood well, but applications of SFP are still challenging Investigation/control of molecular electron dynamics Stronger, shorter, shorter-wavelength EUV pulses λ~nm τ = 80 as @ ~100 ev E = 50 nj @ 13 nm, E = 50 nj @ 13 nm From HH-IR pump-probe to HH-HH pump-probe More details http://www.attoworld.de/ Krausz, Rev. Mod. Phys. 81, 163 (2009) Winterfeldt, Rev. Mod. Phys. 80, 117 (2008) Gaarde, J. Phys. B 41, 132001 (2008) SFP: Perspectives
Relativistic, collective, laser-plasma interaction 1. U p I p (ev) instantaneous plasma generation where I p ionization potential 2. U p kt e (kev) collective plasma 3. U p > m e c 2 (MeV) relativistic interaction Relativity in action in many-body systems (plasma) dominated by collective behavior Macchi, A Superintense Laser-Plasma Interaction Theory Primer, 2013 RLPI: Characteristics
In relativistic regime, longitudinal motion, non-locality, and inertia increase are introduced a 0 = 0.01 (I = 2.1 10 14 W/cm 2 ), LP z x λ a 0 = 1 (I = 2.1 10 18 W/cm 2 ), LP λ x z RLPI: Single electron under a laser field
Relativistic mass increase modifies the refractive index (mildly) relativistic refractive index η = 1 ω p 2 ω 2 γ 0 = 1 4πe2 n e m e γ 0 where ω 2 p = 4πe2 n e, γ m 0 = 1 + a 2 0 e 2 v p = c η and v g = c η At the beam center Higher intensity: γ 0, η, v p, v g More ionization: n e, η, v p, v g Ponderomotive channeling: n e, η, v p, v g RLPI: Relativistic laser pulse propagation
Plasma focuses relativistic pulses Relativistic self-focusing Power threshold to overcome diffraction X P c 17.5 ω ω p 2 GW phase front Ex.) n e = 10 17 10 19 cm 3, P c = 2 10 TW http://www.mpq.mpg.de/lpg/research/rellasplas/rel- Las-Plas.html RLPI: Relativistic laser pulse propagation
Plasma can be more transparent to relativistic pulses Relativistic self-transparency η 0 reflection Cut-off frequency ω c = ω p γ 0 Cut-off frequency lowering Pulse cleaning http://www.mpq.mpg.de/lpg/research/rellasplas/rel- Las-Plas.html RLPI: Relativistic laser pulse propagation
Plasma steepens relativistic pulses Relativistic self-steepening Stronger parts have higher v g s. Formation of an optical shock http://www.mpq.mpg.de/lpg/research/rellasplas/rel- Las-Plas.html RLPI: Relativistic laser pulse propagation
Laser pulses excite plasma oscillations, i.e. laser wakefield Optimum excitation condition pulsewidth 1 ω p Gibbon, Short Pulse Laser Interactions with Matter, 2005 Relativistic laser pulse propagation
Laser wakefield can accelerate electrons up to GeV Electrons are accelerated where E x < 0 (width = λ p 2 ) E x m ecω p 2 γ e max 1 GV/cm Cf). RF accelerator, E x MV/cm The fundamental speed limit bring coherence and stability: relativistic coherence (Tajima) Gibbon, Short Pulse Laser Interactions with Matter, 2005 RLPI: Relativistic laser pulse propagation
A Large-scale simulation is a must ALPS (APRI Laser Plasma Simulator ) Particle-in-cell Maxwell-Vlasov equations 1D3V, 2D3V, and 3D3V Written in C Lorentz boost implemented Under continuous development CompNet (Snow White & Dwarfs) RLPI: A few examples from APRI/CoReLS research activities
Multiple self-injection produces multiple spectral groups Nature Photonics 2, 571, 2008 RLPI: A few examples from APRI/CoReLS research activities
Seeded acceleration can produce more energetic electrons arxiv:1307.4159, accepted by Phys. Rev. Lett. RLPI: A few examples from APRI/CoReLS research activities
The plasma with L/λ 1 can generate stronger, higher harmonics Self-induced Oscillating Flying Mirror Nature Comm. 3, 1231, 2012 RLPI: A few examples from APRI/CoReLS research activities
Intense laser pulse can accelerate protons collectively. Acceleration of protons by collective electrons arxiv:1304.0333 RLPI: A few examples from APRI/CoReLS research activities
RLPI is rich! Relativistic nonlinear physics Relativistic coherence Extreme conditions Non-locality Cf.) atomic nonlinear physics Inherent coherence, limited field strength, mostly local Ultrarelativistic laser-matter interaction Radiation reaction Direct proton drive Photo-nuclear processes Relativistic engineering Particle/radiation sources Plasma as optical components Laboratory astrophysics Scaled-downed experiments of astrophysical/early-universe processes Extreme conditions achievable with lasers E (quasistatic) B (quasistatic) Temperature Pressure With conventional means 10 6 V/cm (accelerator) 10 6 gauss (superconducti ng magnet) With lasers 10 12 V/cm 10 10 gauss 10 9 K (Tokamak) 10 12 K 10 5 bar (diamond anvil) 10 11 bar RLPI: Perspectives
IBS Center for Relativistic Laser Science PW Ti:Sapphire Laser (1) Beam line I: 30 fs, 1.0 PW @ 0.1 Hz (2) Beam line II: 30 fs, 1.5 PW @ 0.1 Hz 100-TW Laser: Dt = 30 fs, E = 3 J @ 10 Hz
PW Ti:Sapphire Laser