Laser-Induced Microexplosions:creating stellar conditions on an optical bench

Chris B. SchafferAndré Brodeur

José GarciaEric Mazur

Hong Kong University

23 October 1999

Introduction

Introduction

microstructuring of transparent materials

Introduction

microstructuring of transparent materials

laser surgery

Introduction

microstructuring of transparent materials

laser surgery

electronic and structural transitions

Introduction

microstructuring of transparent materials

laser surgery

electronic and structural transitions

laser assisted chemistry

Introduction

5 mm

Introduction

Introduction

transparentmaterial

objective

100 fs

focus laser beam inside material…

Introduction

transparentmaterial

objective

100 fs

high intensity at focus…

Introduction

transparentmaterial

objective

100 fs

… causes nonlinear ionization…

Introduction

transparentmaterial

objective

and microscopic bulk damage

Introduction

laser field ionization

multiphoton…

Introduction

laser field ionization

…or tunneling

Introduction

avalanche ionization

free carrierabsorption…

Introduction

avalanche ionization

…and impactionization

Introduction

Damage mechanisms:

explosive

thermal

defect forming

Introduction

Applications:

data storage

Introduction

Applications:

data storage

Introduction

Applications:

data storage

photonic devices

Introduction

Applications:

data storage

photonic devices

internal micromachining

Outline

Damage morphology

Energy deposition

Dynamics

Damage morphology

40 nJ, 120 fs0.65 NA

Corning 0211

3 µm

Damage morphology

3 µm distance (µm)

inte

nsity

0

100

200

300

0 62 4

top view

250 nm

Damage morphology

3 µm40 nJ, 120 fs

0.65 NACorning 0211

Damage morphology

3 µm distance (µm)

inte

nsity

0

100

200

300

0 62 4

side view

2 µm

Damage morphology

10 µm100 fs1.4 NA

Corning 0211

mo

re s

ho

tsmore energy

Damage morphology

20 µm25,000 shots at 25 MHz

4.5 nJ, <100 fs1.4 NA

Corning 0211

Damage morphology

Electron Microscopy:

explosive damage

forms voids

100 fs, 500 nJ0.65 NA

fused silica

Damage morphology

summary of damage mechanisms

single shot multiple shot(25 MHz)

low energy

high energy

Damage morphology

summary of damage mechanisms

single shot multiple shot(25 MHz)

low energy

high energy explosive

Damage morphology

summary of damage mechanisms

single shot multiple shot(25 MHz)

low energy thermal

high energy explosive

Damage morphology

summary of damage mechanisms

single shot multiple shot(25 MHz)

low energy ? thermal

high energy explosive

Outline

Damage morphology

Energy deposition

Dynamics

Energy deposition

Optical microscopy

Transmission

Dark field scattering

Determine threshold for damage:

Energy deposition

optical microscopy

Energy deposition

optical microscopy

6.6 nJ

Energy deposition

laser energy (µJ)

tran

smis

sion

damage criticalself-focusing

0

1.0

101

100

10–1

10–2

10–3

10–4

800 nm, 110 fs0.65 NA

fused silica

transmission of pump beam in fused silica

Dark-field scattering

Energy deposition

sample

objective

block probe beam…

Energy deposition

sample

detector

objectiveprobe

…bring in pump beam…

Energy deposition

sample

detector

objective

pump

probe

…damage scatters probe beam

Energy deposition

sample

detector

objective

pump

probe

Energy deposition

time (µs)

fused silica1.0 µJ

sign

al (

a.u.

)

–0.2 0 0.2 0.4 0.6 0.8

3

2

1

0

Energy deposition

numerical aperture

thre

shol

d (n

J)

0

100

200

0 1.50.5 1.0

vary numerical aperture in Corning 0211

Energy deposition

numerical aperture

thre

shol

d (n

J)

0

100

200

0 1.50.5 1.0

minimal self focusing, sospot size determined by:

and thus

E �I�

(NA)2

I �E

�A�

E�

(NA)2

Energy deposition

numerical aperture

thre

shol

d (n

J)

0

100

200

0 1.50.5 1.0

fit gives threshold intensity: Ith = 2.5 x 1017 W/m2

Energy deposition

bandgap (eV)

thre

shol

d in

tens

ity (

1017

W/m

2 )

3 5 7 9 11

6

5

4

3

2

1

threshold fluence (kJ/m2)

0.6

0.4

0.2

numerical aperture

thre

shol

d (n

J)

0

100

200

0 1.50.5 1.0

Energy deposition

bandgap (eV)

0211

SF11

CaF2

fusedsilica

thre

shol

d in

tens

ity (

1017

W/m

2 )

3 5 7 9 11

6

5

4

3

2

1

threshold fluence (kJ/m2)

0.6

0.4

0.2

vary material…

Energy deposition

bandgap (eV)

0211

SF11

CaF2

fusedsilica

thre

shol

d in

tens

ity (

1017

W/m

2 )

3 5 7 9 11

6

5

4

3

2

1

threshold fluence (kJ/m2)

0.6

0.4

0.2

threshold increases with bandgap…

Energy deposition

bandgap (eV)

0211

SF11

CaF2

fusedsilica

thre

shol

d in

tens

ity (

1017

W/m

2 )

3 5 7 9 11

6

5

4

3

2

1

threshold fluence (kJ/m2)

0.6

0.4

0.2

…but not very much

Energy deposition

bandgap (eV)

thre

shol

d in

tens

ity (

1017

W/m

2 )

3 5 7 9 11

6

5

4

3

2

1

threshold fluence (kJ/m2)

0.6

0.4

0.2

800 nm400 nm

same trend at 400 nm

Outline

Damage morphology

Energy deposition

Dynamics

imaging setup

Dynamics

sample

objective

imaging setup

Dynamics

sample

objective

pump

imaging setup

Dynamics

sample

objective

imaging setup

Dynamics

sample

objective

probe

CCD

Dynamics

sapphire

3 µJ pulse

3.8 ns delay

40 µm radius

Dynamics

water (“self-healing”)

1.0 µJ pulse

35 ns delay

58 µm radius

Dynamics

Dynamics

time (ns)

sapphire

radi

us (

µm)

500

400

300

11.4 µm/ns

200

100

00 10 20 30 40 50

3 µJ

Dynamics

time (ns)

water

radi

us (

µm)

500

400

300

1.48 µm/ns

200

100

00 10 20 30 40 50

1 µJ

Dynamics

time (ns)

water

radi

us (

µm)

100

80

60

40

20

00 10 20 30 40 50

1 µJ

Dynamics

water

1 µJ

time (ps)

radi

us (

µm)

0.1 1 10 100 1000

10

8

6

4

2

0

time-resolved scattering setup

Dynamics

sample

detector

objectiveprobe

time-resolved scattering setup

Dynamics

sample

detector

objective

pump

time-resolved scattering setup

Dynamics

sample

detector

objective

time-resolved scattering setup

Dynamics

sample

detector

objectiveprobe

time-resolved scattering setup

Dynamics

sample

detector

objectiveprobe

signal proportional to area of scatterer

Dynamics

water

1 µJ

time (ps)

radi

us (

µm)

0.1 1 10 100 1000

10

8

6

4

2

0

Dynamics

water

1 µJ

100 µm/ns!

time (ps)

radi

us (

µm)

0.1 1 10 100 1000

10

8

6

4

2

0

Conclusions

submicron-scale bulk micromachining

weak bandgap and wavelength dependence

only a few nanojoules required

Laser micromachining simplified

5-nJ threshold: unamplified micromachining

Laser micromachining simplified

5-nJ threshold: unamplified micromachining

Laser micromachining simplified

waveguide machining

Laser micromachining simplified

waveguide machining

Future applications

Photonic devices

Future applications

Photonic devices

Wavelength-selective splitter

wavelength selective splitter

Future applications

wavelength selective splitter

Future applications

wavelength selective splitter

Future applications

wavelength selective splitter

Future applications

Future applications

Photonic devices

Wavelength-selective splitter

Photonic bandgap materials

Open questions

Propagation of pulses

Mechanisms

Funding: National Science Foundation

Acknowledgments:Prof. Alex Gaeta (Cornell)

Prof. Nico Bloembergen (Harvard)W. Leight

Carl Zeiss, Inc

For a copy of this talk andadditional information, see:

http://mazur-www.harvard.edu