Theoretical Study of the Optical Manipulationof Semiconductor Nanoparticles

under an Excitonic Resonance Condition

+ Reference +　

T.Iida and H.Ishihara, Phys.Rev.Lett. 90, 057403(2003)

ITOH Lab. 　　 Kei IMAIZUMI （ M1 ）

Abstract

“Manipulation” means “skillful handling”.

Optical manipulation is the technique of handling small objectsusing mechanical interaction between light and matter.

Force

・ Manipulating the semiconductor nanoparticle・ Size selective manipulation

Contents

• IntroductionApplication, History

• Maxwell stress tensor method• Calculation Result

The merit of using electronic resonanceHeat problemSize selective manipulation

• Summary

Application

Handling of DNAT. T. Perkins,

D. E. Smith, S. Chu(1994)

Biology, Chemistry, Material engineering…

Kansai Advanced Research Centerhttp://www-karc.nict.go.jp/

Polystyrene bead with a diameter

of 1 μm captured by laser

History of optical manipulation

19c

196019701985

1986

1995

Lorentz derived the equationof motion of a charged particle.Laser was invented.A.Ashkin accelerated micro-size particles by laser.Laser cooling of atoms

A.Ashkin demonstrated the trapping of dielectric particlewith single focused laser beam.Bose Einstein condensation of atoms

1997 Nobel PrizeS.Chu, C.Cohen-Tannoudi, W.D.Phillips

2001 Nobel PrizeE.A.Cornell, W.Ketterle, C.E.Wieman

Difficulty of manipulating nano-particles

Electronic Resonance• Manipulating the nano-particles• Size selective manipulation

Atomic scaler λ≪

μmr λ≫

nm

difficultex.)atom trapping

ex.)optical tweezer

Forces

Scattering force, Absorbing force Gradient force

Resonance

The interaction between light and matter increases.

Maxwell stress tensor methodLorentz Force

Maxwell Equations

< > : 　 time average

T : Maxwell’s stress tensor

n : normal vector

　 S : Surface of the matter

volume integral

surface integral

resonance

susceptibilityEob ， Δob

constant depending on the object

object Incident electric field

About the resonance

P

Escat

resonantnonresonant

P Escat

ε ： Resonance P ： large Escat ： large

drEP

14

1

laserob

bbb EE

The merit of using electronic resonance

Greater advantage of resonance about smaller object!

ObjectCuCl particle

hwt = 3.2022 [eV]

R=100nm

R=50nm

The size dependence of its maximum value in the energy range 0 ~ 4 eV.

100nm → No difference 10nm → 104 times lager

Handling smaller object 　　　　　 Resonance light

Heat problemAbsorption Heat problem

R=50nm

〈 I 〉

〈 II〉

〈 III 〉

<I>,<III> ・・・ Scattering　　　　　 Prevent the heat problem<II> ・・・ Absorption

Size selective manipulation

• Quantum size effect-Discrete energy levels-Energy shift depends on the size

Energy level

Future

Application to nanotechnology.

Particular particles

Propagating plane wave

Image

Summary

• When the size is less than 100nm, the use of electronic resonance has the merit.

• The exerted acceleration increases as the size decreases.

• The peak position of the force sensitively varies with the size change.

Nanoscale size selectionnanotechnology

Optical tweezer

Glass sphere (dielectric particle)

21 nn 2n

1n

lens

Force

p

laser

Force~ pN

R>>λ

μm

Gradient ForceUniform electric field

+

+

+

sloping electric field

－

－

－

cancel each other

+

+

+

－

－

－

E E

total force

In the sloping electric field, the power works.

Quantum size effectDiscrete energy levels

Energy shift depends on the size

2

22

2MRE

E dot size

Size change Energy gap change

Atom Semiconductor nanoparticle (quantum dot)

Quantum dot laser

Quantum dot laser・ Laser wavelength depends on the dot size.

・ Low threshold.

・ Stable property at high temperature.

threshold ：しきい値

Useful property↑

The same size dots are needed.

Maxwell stress tensor method

Lorentz Force (of N charges)

G(t) is the summation of momenta