Presented By Under supervision 1 Department of Physics, Nagoya - - PowerPoint PPT Presentation

Under supervision

1 Department of Physics, Nagoya University, Nagoya, 464-8602, Japan 2 National Institute for Fusion Science, Toki, Gifu 509-5292, Japan

Presented By

Content

➢Introduction ➢Aim ➢Hypothesis ➢Method ➢Results and Discussion

▪ Formation Mechanism of Periodic Nanograting Structure By Weibel

Instability

▪ Formation Mechanism of Periodic Nanograting Structure By Surface Plasma

Wave

➢ Conclusion

Introduction

❑ Nanomaterial: Is define as a material with structure size(in at least one dimension) in nanoscale(1 nm = 10−9 m). Nanoscale is refer to structure with length scale of 1 to 100 nm. ❑ Nanograting structure: It is kind of periodic structure has been observed on the surfaces of the materials after irradiating it with laser beam of different intensity. The first observation for the periodic nanograting structure was 1999. Periodic nanograting structures are one of the contemporary science issues that gained much attention in the last 20 years due to their vast usage in industrial applications. ❑ This structures is called LIPSS ( Laser Induced Periodic Surface Structures).

What Is the Periodic Nanograting Structure?

➔LIPSS ( periodic nanograting structure) has following characteristics: ◆The periodicity is usually less than laser wavelength. ◆The groove direction is perpendicular and/or parallel to laser polarization direction. ➔ Periodic nanograting structure is produced by repeating irradiation of femt femtose

• second

cond laser pulses with the intensity about 1013 W/cm2 or higher.

Copper Dt = 100 fs d = 40 mm l = 800 nm Intensity ~ 1013 W/cm2

Interspaces of LIPSS were in the range of 0.5λL – 0.85λL

Courtesy to Prof. M. Hashida ? cm

Application of the Periodic Nanograting Structure

❑ Friction reduction: ❑ Metal coloring:

Φ=30 [mm] SCM415(alloy steel) 25% reduction

• T. Kato and N. Abe,

Laser Research 37,510 (2009) A.Vorobyev, et al., Laser Photonics B. Rev. 1-23 (2012)

Aim

❑ Producing and controlling periodic nanograting structure is my major duty. ❑ Investing and explaining formation mechanism of periodic nanograting structure under the

effect of relativistic and nonrelativistic laser beam is the second major duty.

❑ Study the accompanied physics related to formation mechanism of periodic nanograting

structure is the keywords of the thesis work.

Hypothesis

❑ The maximum laser intensity can be used to produce the periodic nanograting structure in

experimental work is about I = = 10 1013

13– 10

1015

15 W/cm2. Our simulati

ation

• n study

dyin ing g case contain ined ed two cases es with h relativ ivist istic ic and nonrelat ativi ivistic stic laser r beam of intensity ity I = = 10 1018

18 W/cm2 - μm2 and

I = 10 1016

16 W/cm2 - μm2.

❑ Many researches assume that surface plasma wave has a role in forming periodic nanograting

structure but without any evidences. Within in this s simulati ation

• n study

dy we can get a c clear eviden ence ce to existen ence ce of surface ce plasm sma wave and explain ain its role in formation ion mechan anism. ism.

❑ Getting periodic nanograting structure by using relativistic laser beam can be considered as the

first trial in this field. We could d expla lain in this s case by using relativi ivist stic ic laser r intensi sity.

Method

The particle article-in in-cel cell ( PIC) PIC) code code is used to study plasma physics by researchers. PIC code compute both of Maxwell’s equations and equations of motion for electrons and ions in 2D space and 3D velocity space.

❖ Computer Physics Communications 204 (2016) 141–151

❑ The experimental system ❑ The simulation system

Systems Comparison

Metal Pre-formed plasma Target Plasma Mimic plasma Laser Laser

Sample Sample

Part I The Formation Mechanism of Periodic Nanograting Structure by Weibel Instability

Result and Discussion

The Simulation Parameters

❖ Plasma Parameter:

• Mi／me = 1836
• A = 1, Z = 1
• Te = 1.0 , Ti = 0.1 keV

✿ Target plasma – X = 2.0 〜12.0 µm – Y = -3.6 〜3.6 µm – ntarget = 10 ncr ✿ Mimic plasma – X = 0〜2.0 µm – Y = -3.6〜3.6 µm – nthin = 0.7 ncr

❖

Laser Parameter: λL = 800 nm incidence angle = 0° τrise = 15 fs, p-polarized, plane wave IL= 1018 W/cm2-µm2 continuously irradiated beam The Max experim rimen ental tal I= 10 1013

13 ~10

1015

15 W/cm2

✿ simulation Time : 0 ~ 500 fs

Simulation Results

• Electron density profile in the x-y

plane at snapshot t = 250 fs. The periodic nanograting structure

• bserved as self-organized structure

along the boundary between mimic plasma and target plasma at t = 250

• fs. 13 tips are formed along y-axis

from -3.0 to 3.0 µm, and the average interspace size of 0.46 µm is shorter than the laser wavelength of 0.8 µm.

t =150 0 fs fs t =200 0 fs fs

Electron Density Profile x-component of electron current density z-component of magnetic field

Current density ( Jxe) and magnetic field ( Bz) in a relation with time development.

: The maximum amplitude of Jxe and Bz : The minimum amplitude of Jxe and Bz

Current density (J/encrc)

Weibel Instability can be understood simply as the result of the superposition of two counter-streaming beams

Result and Discussion

Part II The Formation Mechanism of Periodic Nanograting Structure by Surface Plasma Wave

The Simulation Parameters

❖ Plasma Parameter:

• Mi／me = 1836/16 = 114.8
• A = 1, Z = 1
• Te = 1.0 , Ti = 0.1 keV

✿ Target plasma – X = 2.0 〜12.0 µm – Y = - 10.0 〜 10.0 µm – ntarget = 10 ncr ✿ Vacuum is surrounded target plasma everywhere.

❖

Laser Parameter: λL = 800 nm incidence angle = 0° τrise = 5 fs, p-polarized

10

• 10

Y X 2 12 Target Plasma

flattop shape (f = 10 µm) IL= 1016 W/cm2 - μm2 continuously irradiated beam The Max experimental I= 1013 ~ 1015 W/cm2 ✿ simulation Time: 0~500 fs

The electron density profile in the x-y plane in snapshots taken at (a) t =150 fs, (b) t =200 fs, (c) t = 250 fs, (d) t = 300 fs,(e) t = 350 fs,(f) t = 400 fs, (g) t = 450 fs, and (h) t = 500 fs.

t = 150 0 fs fs t = 200 0 fs fs t = 250 0 fs fs t = 300 0 fs fs t = 350 0 fs fs t = 400 0 fs t = 450 50 fs t = 500 0 fs fs

t = 300 fs Intermediate area Sparse area Y [micron]

Average electron density (ne/ncr) versus distance x (µm) with different density at (a) t = 200, (b) t = 300, (c) t = 400, and (d) t = 500 fs.

ninter~ 5 5 ncr

cr

nsparse~ 0.1 ncr

cr

The used relation to calculate wavelength of SPW is depend on nsparse and ninter

𝜇𝑡𝑞 𝜇𝑀 = 2 − (𝑜𝑡𝑞𝑏𝑠𝑡𝑓 + 𝑜𝑗𝑜𝑢𝑓𝑠 𝑜𝑑𝑠 ) (1 − 𝑜𝑡𝑞𝑏𝑠𝑡𝑓 𝑜𝑑𝑠 )(1 − 𝑜𝑗𝑜𝑢𝑓𝑠 𝑜𝑑𝑠 )

The used relation to calculate wavelength of SPW is depend on nsparse and ninter 𝜁 = 1 −

𝜕𝑞𝑓

2

𝜕𝑀

2 = 1 −

𝑜𝑓 𝑜𝑑𝑠,

𝜁: is the permittivity of medium 𝑙𝑡𝑞 = 𝑙𝑀 𝜁𝑗𝑜𝑢𝑓𝑠. 𝜁𝑡𝑞𝑏𝑠𝑡𝑓 𝜁𝑗𝑜𝑢𝑓𝑠 + 𝜁𝑡𝑞𝑏𝑠𝑡𝑓

Surface Plasma Wave ( SPW)

𝜕𝑡𝑞 = 𝜕𝑀 Wavelength of SPW with different density values. The graph is drawn for the range nsparse = 0 ~ 0.9 ncr and ninter = 1 ~ 5 ncr

Standing wave and Ponderomotive force

• The mechanism of surface plasma wave (SPW)

generation is based on the collective behavior of the excited electrons in the y-direction due to the electric field component of the laser beam.

• The

bidirectional collective behavior

• f

the electrons in both positive and negative y-axis, leads to SPW propagation near to the interface, producing the so- called standing wave. The ponderomotive force of standing wave plays a major role in forming seeds or tips for the development of periodic nanograting structures at early stages since it is repeated each 𝛍sp/2 .

e e

x y EL 𝜕𝑡𝑞 = 𝜕𝑀

Define the position of pressure balance PL=Pp. 𝑄𝑀 = 2𝐽𝑀 𝑑 = 6.67𝐽𝑀 𝑋/𝑑𝑛2 𝑁𝑐𝑏𝑠 , 𝑄

𝑞 = 1.79 𝑜 𝑈𝑓 𝑙𝑓𝑊 /𝜇𝑀 2[𝜈𝑛][𝑁𝑐𝑏𝑠].

The position at which the pressure got balanced is at density n = 2.384 ncr is the interface position.

time (fs) ninter/ncr nsparse/ncr 𝛍sp/𝛍L 200 4.58 0.10 0.91 300 4.83 0.14 0.95 400 5.26 0.17 0.98 500 5.51 0.19 1.00

➢ Specify nsparse and ninter as the first local minima on the left hand side and x1,2 (µm) as the first local maxima on the right hand side of x1,2 (µm). ➢ We can calculate wavelength of SPW from the previous relation.

Comparison graph between the simulation and theoretical interspace.

Time (fs) Theoretical Interspace 𝛍sp/2 (µm) Simulated Interspace (µm)

200 0.36 0.26 300 0.38 0.33 400 0.39 0.40 500 0.40 0.50

Oscillating Two Stream Instability

❑ Since there is a density perturbation in the

intermediate area of the plasma due to the Fp of SPW and because the system is under the effect of the laser electric field EL , the surface electrons will continue oscillate and move in a direction opposite to the EL producing an electric field E1 .

❑ In contrast, ions do not move on a similar time

scale of 𝝏L and density ripples causes a charge separation.

❑ A new nonlinear ponderomotive force related to

OTS FnL governs the total field EL+E1 as pointed

• ut as shown in graph.

❑ This nonlinear pondermotive force is push up the

density and enlarge their sizes.

L

• F. Chen. Introduction to plasma physics and controlled
• fusion. Springer International Publishing.

The Oscillating two stream instability can be calculating after using ninter according to the following relation:

Where: Q = ω2, Since ω = ωreal + iγoTs ao: laser parameter and depend on laser intensity. ෝ 𝜕𝑞𝑓

2 : is the electron density in the intermediate area and equal 𝒐𝒋𝒐𝒖𝒇𝒔 𝒐𝒅𝒔 .

෡ 𝒍𝑞𝑓

2 : is the normalized wavenumber of the surface plasma wave. 𝑛𝑓 𝑁𝑗 : is electron to ion mass ratio.

This graph has been drawn at ෡ 𝒍𝒕𝒒

𝟑 =1, 𝒃𝒑 𝟑 =0.5

𝑅3 − 2 + ෝ 𝜕𝑞𝑓

2

𝑅2 + 1 + 2 ෝ 𝜕𝑞𝑓

2 − 2෠

𝑙𝑡𝑞

2 𝑏𝑝 2 𝑛𝑓

𝑁𝑗 𝑅 − ෝ 𝜕𝑞𝑓

2 + 2෠

𝑙𝑡𝑞

2 𝑏𝑝 2 𝑛𝑓

𝑁𝑗 = 0

The growth rate of oscillating two stream instability in a relation with time enhancement.

Time (fs) ෝ 𝜕𝑞𝑓

2

෡ 𝒍𝑞𝑓

2

𝛿𝑝𝑢𝑡 𝜕𝑀 200 4.58 1.0989 0.0037 300 4.83 1.0526 0.0034 400 5.26 1.0204 0.0031 500 5.51 1.0000 0.0030

If 𝛿𝑃𝑈𝑇𝑈 = 1, then T = 100 fs is required to grow up growth rate of value = 0.004 This proof the existence of

• scillating two stream

instability within our simulation time ( from 0 to 500 fs). 𝑏𝑝 = 0.85 𝜇𝑀[𝜈𝑛] 𝐽 [1018 𝑋/𝑑𝑛2]= 0.085

Conclusion

➔ Periodic nanograting structure can be formed by using relativistic laser

pulse of 1018 W/cm2-µm2 and nonrelativistic laser beam 1016 W/cm2- µm2 .

➔ We have used hydrogen plasma in order to speed up calculation rate. ➔ Significant results have been obtained

and we could explain the physical phenomena by using of the Weibel instability, surface plasma wave and oscillating two stream instability .

Plasma Simulation Analysis for Formation Mechanism of Periodic Nanograting Structures by Laser Pulses

Acknowledgement

❑ I would like to thank both of JASSO and MEXT organizations for giving me the financial support to stay in Japan and cover my research period.

❑

Number of Scholarships: JASSO: 91306004993 and MEXT: 144104 .

❑ I would like to appreciate my colleagues in Egyptian Atomic Energy Authority for all facilities and years that were given to me in order to finish my Ph.D. in Japan. ❑ I would like to appreciate all professors, friends, family for all their supports.

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