Interaction of plasmas with intense laser pulses carrying orbital - - PowerPoint PPT Presentation

Interaction of plasmas with intense laser pulses carrying orbital angular momentum

John Adams Institute for Accelerator Science Lecture Series 14.04.2016 Zsolt Lecz, Alexander Andreev, Andrei Seryi, Ivan Konoplev

04/14/16 Zsolt Lecz 2

Content

➔ Introduction, motivation ➔ Circularly polarized (CP) intense pulse interacting with

solid density targets

➔ Laser induced Coherent Synchrotron Emission (CSE) ➔ Attopulse and attospiral generation ➔ Screw-shaped pulses interacting with underdense

plasmas

➔ Generation of GigaGauss axial magnetic fields ➔ Possible applications in LWFA

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Orbital Angular Momentum (OAM)

⃗ r ⃗ p

Particles EM Waves

⃗ r ⃗ S y z

⃗ S=(⃗ E×⃗ B) μ0 r=√ y

2+z 2

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Synchrotron radiation

I (ω)∼|∫dt ⃗ ϵ×[⃗ ϵ×J (⃗ r ,t)]exp[i ω(t−⃗ ϵ⋅⃗ r /c)]|

2

Observer

⃗ r ⃗ ϵ ⃗ v ⃗ J ⊥

I (ω)∼|J ⊥(x ,t )exp[i ω(t−x(t)/c)]|

2

⃗ v ⊥≪c ⃗ v x≈c

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Synchrotron radiation

I (ω)∼|∫dt ⃗ ϵ×[⃗ ϵ×J (⃗ r ,t)]exp[i ω(t−⃗ ϵ⋅⃗ r /c)]|

2

Observer

⃗ r ⃗ ϵ ⃗ v ⃗ J ⊥

I (ω)∼|J ⊥(x ,t )exp[i ω(t−x(t)/c)]|

2

x(t)=r(t)=? γ=(1−˙ x(t )

2/c 2) −1/2

¨ x(t)∼t

2n−1⇒ωr∼γ 2n+1 n

I (ω)∼ω

−2n+2 2n+1

⃗ v ⊥≪c ⃗ v x≈c

• D. an der Brügge and A. Pukhov, arxiv:1111.4133 (2011)

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Twisted pulses (using electron beams)

Erik Hemsing et al., Nature Physics 9, 549 (2013)

• Gy. Toth et al., Optics Letters 40, 4317

(2015)

Electron gamma: 100-1000 Undulator length: ~cm-m

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Simulation setup: Solid density target, CP pulse

Codes:

✔ Vsim (VORPAL), Tech-X

Corp.

✔ EPOCH

Collissionless, relativistic particle-in-cell plasma simulations. a0=√ I [W /cm

2]λ L 2[μm]

1.4×10

18

Normalized laser amplitude

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CP pulse vs. flat foil

I L=10

20W /cm 2

t L=20fs wL=2μ m

h=0.2μ m n0=28ncr solid hydrogenfoil

Simulation parameters:

y x z

• Zs. Lécz et al., LPB 34, p. 31-42 (2016)

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Attopulse generation

y x z

Electron nanobunches

Relativistic electrons near the plasma surface emit coherent radiation.

v∥≈c v ⊥≈0 a⊥≈ eA0 meω0

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Rotation symmetric interaction: CP pulse vs. cone-like targets

Cylinder target Energetic electrons move on a spiral path Cone target Focusing of attospiral near the exit hole

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Movie

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OAM in attopulse

1μ m 0.4μ m

Transversal poynting vector Incident pulse Attospiral

Max :10

24 W

m

2

Max :1.4×10

25 W

m

2

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Coherent Synchrotron Emission

Electrons

E y<0 E y

2

Ez

2

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Coherent Synchrotron Emission

Electrons

E y<0 E y

2

Ez

2

E y(t)=−N e c

2R

a y(t ' ) (1−vx(t ')/c)

2

=−C a y(t ' ) 4 γ

4

(1+α1 γ

2t ' 2n) 2

x'=x−c(t −t ')

v x(t ' )=v0(1−α1t '

2n)

t ' (t)

J.M. Mikhailova et al., PRL 109, 245005 (2012)

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Harmonic spectrum

• Zs. Lécz and A. Andreev, PRE 93, 013207 (2015)

t atto=0.21 Ndr

−1t L, I atto=(Ndr /2) 2 I ω0

Ndr=ωdr/ωL≈(3/2)a0

2

I ω0=?

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Screw-shaped laser pulse

Front View: The ponderomotive force has an azimuthal component as well! The laser pulse is represented by the envelope function of the intensity distribution.

F p∼∇ I LλL

2∼(I L/λsp)λL 2

λsp/2

http://arxiv.org/abs/1604.01259

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Envelope model

EM wave Inensity Mesh resolution

F p F p

Fp=e ⃗ v×⃗ B∼⃗ E×⃗ B ∼E ∂ E/∂ x∼∇ Eenv

2 ⋅[1+cos(2k x)]

If the electron plasma period is much larger than the laser period:

F p∼∇ I L

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In the back of the bubble.

Electron dynamics

In the moving frame of the laser pulse!

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Bubble solenoid

ne/n0 Bx(kT) ×1027 m−3

The plasma has to be underdense, otherwise the pulse depletion becomes significant.

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Scaling of peak magnetic field

B∼(γ n0)

1/2

γ∼I L λL n0<0.1ncr=λL

−21.12⋅10 14 m −1

For larger B-field small wavelength and high intensity is required!!

B=1 MT ⇒n0=7⋅10

28m −3,λL=20nm , I L=8×10 23W /cm 2

B=50 kT ⇒n0=7⋅10

28m −3,λ L=800nm,I L=2×10 22W /cm 2

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Parameter map

k=n0/ncr λ p=2πc/ω p=plasma wavelength λ L=100nm λ L=800nm

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Electron collimation: Low emittance via synchrotron cooling?

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Steady solenoid

The plasma wavelength is smaller than the laser pulse length (or spiral step). In this regime bubble can not be formed, but rotational current is generated behind the pulse. The length and lifetime of the uniform axial field depends on the depletion time and diffusion time respectively. 100 micrometers long for 100 fs

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Future plans

• Electron cooling via

synchrotron emission

• Near the laser axis

higher grid resolution is needed

• Improved beam

emittance? New short wavelength source ?

• Generalize the driver

beam: does it work with e-beam as well?

• Project 1

Project 2

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Multi-scale problem

e-

⃗ Bx

Speed of light Record the absorbed EM wave

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Thank you for your attention!

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Twisted pulses (using plasmas)

Yin Shi et al., Physical Review Letters 112, 235001 (2014) In gas target: Carlos Hernandez-Garcıa et al., Physical Review Letters 111, 083602 (2013)

The wavefront of the incoming pulse is distorted by the tailored spiral-shaped surface. OAM conversion of Laguerre- Gaussian pulses Attosecond UV vortex

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Collimated electron and ion beams

Axial magneic field:

• N. Naseri et al., PHYSICS OF PLASMAS 17,

083109 (2010)

Electron trajectories

• S. V. Bulanov et al., JETP Letters, Vol.

71, No. 10, 2000, pp. 407–411

• Z. Najmudin etal., Phys Rev Lett

87, 215004 (2001) Inertial Confinement Fusion:

• T. AKAYUKI , A. & K EISHIRO , N. (1987).

Laser Part. Beams 5, 481–486