Ultrafast nanophotonics

- optical control of coherent electron -

ICTP 18.2.8

Hirofumi Yanagisawa

LMU, MPQ

Hirofumi Yanagisawa

Japan (Tokyo) ⇒ Switzerland (Zurich) ⇒ Germany (Munich)

http://roundtripticket.me/world-map-labled.html/best-image-of-diagram-world-map-and-labeled-for-labled

Laser-induced electron emission

from a metallic tip

1973 1987 2006

CW

laser

Pulse

Laser (ps)

Pulse

Laser (fs)

Slow response

Phonon system

nano-, pico- sec

Ultrafast response

Electronic system

femto-, atto- sec

PRL 30, 1193

Nucl. Instr. And Meth.

A 256,191

PRL 96, 077401

5 Nature series

10 PRL

Ultrafast nanophotonics? Time Size

Size m um nm mm

Time

milli-sec

pico-nano

atto-femto Here!

Nano structure

Ultrafast nanophotonics

Light

http://thescienceofwaves.weebly.com/uploads/2/5/7/8/25786734/1239513_orig.jpg

k

～wavelength (800nm)

Nano-sphere

r=100nm

10-18

Atto

10-15

Femto

10-12

Pico

10-9

Nano

sec

Phonon (lattice) Electron

Coherent phonon

Melting

Laser absorption

El-Ph scattering (heating Ph)

Phase transition

El-El scattering (heating El)

Tunnelling

Rescattering

Quiver

Sub-cycle

Surface Diffusion

Plasmonics

Strong field El: Electron

Ph: Phonon

1st 2nd

2nd

Weak field

Tip

Sphere

Bowtie

Star

Adv. Mater. 26, 2353

Nano-structures

Laser-induced electron emission

from a metallic tip

Reference books

- Principles of Nano-Optics

Novotny and Hecht

- Physics of Surface and Interfaces

Harald Ibach

- Field Emission and Field Ionization

Robert Gomer

We learn today

1. Characeterization of tip apex

2. Beauty of nanophotonics

in laser-induced electron emission from tip

3. Optical control of coherent electron wave

Why electron source?

Let’s learn more about

tip and electron emission

Electron

Best probe for

Nano-object

The TEM picture is taken from

http://www.york.ac.uk/res/nanocentre/facilities/fetem.htm

Electron Microscopy

Nano-object Atom

Dete

cto

r

Electron gun

1nm = 10-9m

Tip Laser

pulse

B. Cho, PRL 92, 246103 (2004)

C. Oshima, Nature 396, 557 (1998)

Brightness

Coherence

Space

Time

Introduction 2 –Electron gun-

P. Hommelhoff, PRL 96, 077401 (2006)

~1fs

M. Aeschlimann, Nature 446, 301 (2007)

~100nm and ~100fs

Electron gun

Pulsed laser

lens

Tip

1fs = 10-15sec ３D Dynamical information

⇒New Phenomena

How can we get electrons?

Surface and work function

Work function

Work functions ⇔ Ionization Energy

(surface) (atom)

Vacuum

EF

Evac

Metal

Work

function Φ

Change

surface to surface

2-6eV

How can we get electrons?

1. Thermal emission

2. Photoemission

3. Field emission

4. Photo-field emission (fs)

5. Optical field emission (as)

How can we get electrons?

Thermionic

emission Photoemission

photon Evac

EF

Evac

EF

J∝T2exp(-Φ/kT) J∝In (n order photon)

e-x

Mesh Grid

-1～-2kV Tip

Field emission

EF

Metal Vacuum

Nanometer sharpness

Surface

Barrier

EF

Metal Vacuum

How thin barrier has to be?

～1nm

Φ 3-6eV F=3-6V/nm

J∝F2exp(-aΦ3/2/bF)

Photo-field emission

photoemission

hν

hν

hν

x

EF

E

optical fieldemission

x

E

Weak field Strong field

Various way to characterize tip apex

Photon and Particle Interactions with Surfaces in Space

Volume 37 of the series Astrophysics and Space Science Library pp 323-330

M. Bujor

1 Langmuir

10-6mbar x 1 second

1.6eV !!

How to make and keep clean surface?

Heating

Ar+

Ar+

Ar+

10-7mbar -> 10 sec

10-8mbar -> 2 min

10-9mbar -> 20 min

10-10mbar -> 3 hr

10-6mbar -> 1 sec

1 Langmuir

10-6mbar x second

Characterization of tip apex

Erwin Mueller (German physist)

First time in history,

individual atoms and their arrangement.

A Biographical Memoir Vol 82

by ALLAN J. MELMED

1. Field emission microscopy (FEM)

Around 1935

2. Field ion microscopy (FIM)

Around 1950

3. Atom probe field ion microscopy

(APFIM)

Field Emission and Field Ionization: Robert Gomer

Magnification: x/br b～1.5

105-106

FEM

Vtip=-2250V

Without laser

Field emission pattern with and without laser

Radius ～ 100nm

Side

Intensity high

low

Tungsten

Tip

(011)

(111)

(111)

(310) (310)

Field Emission and Field Ionization: Robert Gomer

Various Field emission image from W[011]

N2

O2

Clean

FEM pattern

change depending

on adsorbate

Phys. Rev. Lett. 45,

1856 (1980).

Graphene Simulation, Edited by Jian Ru Gong, ISBN 978-953-307-556-3

Spatial resolution => 1 – 2nm

View from

Nano-tip?

Power of FEM

Vtip=-900V

FEM

Nano-tip? Power of FEM

Vtip=-900V

FEM

Positive

bias

Positively

charged

http://labman.phys.utk.edu/phys222core/modules/m2/conductors_in_electrostatics.htm

Experimental set up Field Emission Microscopy

Pre amplifier

Position computer

Resistive

anode

MCP

(Chevron)

Mesh

Grid

High voltage

(negative)

Heating

φ θ

z

y

x

Lens : f=15mm

y

Vacuum

(UHV)

Sample : Tungsten wire

focus

4μm

Air

Oscillator

800nm, 76MHz, 55fs

θp

Laser Polarization

PC

30nm

PL=20mW

Vtip=-2250V

Without laser With laser (800nm)

Vtip=-1600V

Field emission pattern with and without laser

Radius ～ 100nm

Side

Intensity high

low

Tungsten

Tip

(011)

(111)

(111)

(310) (310)

What is physics behind?

Surface electromagnetic wave

Electromagnetic wave couples with surface charge

Surface plasmon polariton: Epsilon_R 0, Epsilon_Im >>0

⇒Phys. Rev. B 44, 5855 (1991).

Photo-field emission Time average

Rapex

=100nm

Max

Min

MaX-1: C. Hafner

http://alphard.ethz.ch/

θp=0 θp=30 θp=60 θp=90 θp=120 θp=150

Propagation of surface electromagnetic waves

k

With laser

Propagation of

Laser

E k

Let’s simulate

laser-induced field emission images

⇒Φ

jexp-jcalc=0

Evac

EF

Photo-field emission

FEM

e-

Field emission

jexp

FDC F=FDC

Work

function

MaX-1: C. Hafner

Simulation of LFEM (photo-field emission model)

Simulation of LFEM (photo-field emission model)

⇒Φ, FDC

jexp-jcalc=0

Evac

EF

Photo-field emission

FEM

∝F2laser

jcalc ⇒ LFEM

f(E)

Flaser

hν

e-

FDC

Experiment

Simulation

θp=0 θp=30 θp=60

θp=90 θp=120 θp=150

Simulations : Photo-field emission model

Exp.

Sim.

Exp.

Sim.

Exp.

Sim.

Exp.

Sim.

Exp.

Sim.

Top

PRL 103, 257603 (2009)

Time ave.

k

With laser

Q1: Upon laser irradiation, which side of apex will be hotter,

laser exposed side or shadow side?

Phys. Rev. B 86, 035405 (2012)

E field

Deposited energy

J/cm3

Electron

Temp.

At 30K

B. Cho, Phys. Rev. Lett. 92, 246103 (2004)

Coherence length ～200nm

Coherence time ～200fs

Tip

What’s nice?

Coherence length ～10nm

At room temperature

Spatio-temporal

control of

coherent electron

emission

Optical control of

Young’s interference

Without laser With laser (7fs, 40mW)

Interference

(111)

(111)

(310) (310)

Pol=10

Pol=90 Pol=110

Pol=40

C

A

B

C

A

D

B B

A

Polarization dependence of interference pattern

Interference

A-B

C-D

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10.8

1

1.2

1.4

1.6

1.8

2

2.2

2.4

2.6x 10

5

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.5

1

1.5

2

2.5

3x 10

5

L

I S

Pol=150 Line profile

L I S

Gaussian

fitting

Data analysis: Gaussian fitting

0 100 2000

1

2

3

4

5x 10

-3 S

0 100 2000

0.002

0.004

0.006

0.008

0.01

L

0 100 2000

1

2

3

4

5x 10

-3

0 100 2000

0.002

0.004

0.006

0.008

0.01

0 100 2000

1

2

3

4

5

6

7

8x 10

-4 I

0 100 2000

1

2

3

4

5

6

7

8x 10

-32*sqrt(S)*sqrt(L)

0 100 2000

1

2

3

4

5

6

7

8x 10

-4

0 100 2000

1

2

3

4

5

6

7

8x 10

-3

0 100 2000

0.002

0.004

0.006

0.008

0.01

S+L

0 100 2000

0.002

0.004

0.006

0.008

0.01

Polarization angle (degree)

(A+B)2=A2+B2+2AB

L S 2*(L*S)0.5

0 0 0 0 0 100 100 100 100 100

L

I S

S L I 2*(L*S)0.5

L+S

Polarization dependence of electron intensity

Potential landscape Simulations : Interference

(111)

(013) Interference

peak

2D TDSE

Far field

Simulations : Energy dependence of interference

Energy

Dependence

Scientific Reports 7, 12661 (2017)

Transmission Probability

Photoemission

Photon Evac

EF

Q2: Do we need quantum mechanical treatment for

transmission probability of photoemission?

Photo-field emission

Photoemission

hν

hν

hν

x

EF

E

10eV

0eV

Surface

9eV

Electron

DeVries, P. L.

A First Course in Computational Physics

(John Wiley & Sons, Inc., 1994)

10eV

0eV

Surface

11eV

Electron

10eV

0eV

Surface

15eV

Electron

k k

Delay

line

Time-resolved electron holography

A k

B k

Delay line

?

Beam Splitter

Such a dense electron source cannot be available.

Introduction of myself

Electron emission from a nano-tip

○How can we get electrons?

-work function

-various ways to emit electrons

○ How to characterize tip apex: FEM

Laser-induced field emission

○Site-selective technique

○Optical control of Young’s interference

Summary

Tomorrow

More about electron dynamics