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2D and 3D Geometries producedby Ultrashort Laser Pulses

http://ssll.inflpr.ro

INFLPR, Bucharest, Romania

Marian Zamfirescu

Workshop on high school physics (12 - 18 July 2010) , Cheia, Romania

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Angstrom10-10 Nanometer10-9 Micrometer10-6

Atoms MoleculesCells

Insects

Millimeter10-3

1m

Meter

1 m300 nm

Nanostructures produced by laser

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Watt1 W Kilo Watt103 W Giga Watt

109 W

Light bulb

HydroelectricPower Station

Extreme light Infrastructure

CO2 Laser

Tera Watt1012 W

TEWALAS Laserat INFLPR

Attoseconds

10-18

Seconds

Processor'sclock time

High speedphotographyChronometer Chemical

reactionsElectrons

movement

Femtoseconds10-15Nanoseconds

10-9Milliseconds

10-3

Peta Watt1015 W

Lasers with high power and ultrashort pulse duration

P=E/t

=E/tP
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Applications of femtosecond lasers

Low pulse energy (nJ)

- Dynamics of chemical reactions;

- High resolution laser scanning microscopy.

Medium pulse energy (mJ)

- laser microprocessing: laser ablation or photo-induced

chemical reactions (material modification by nonlinear

absorption);

- generation of THz radiation.

Ultra intense laser beams (J)

- accelerated electron, X-Rays (TW lasers);

- protons beams, accelerated ions, Gamma rays (PW lasers).

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Laser ablation with sub-micrometer resolution

Two-Photon Photopolymerization (TPP)

Near-field laser lithography

Laser Induced Forward Transfer (LIFT)

Two-Photons Excited Spectroscopy (TPE)

Microprocessing techniques with ultrashort lasers pulses

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Interaction of materials with intense laser beam

Long laser pulses (ns) Focused laser beam create free electronsin the irradiated material.

The free electrons interact with thecrystal lattice heating the irradiated area.

At laser pulses longer than the thermaldiffusion time a large area is heated aroundthe irradiated spot.

When the temperature of the material

reaches the vaporization temperature, thematerial is locally removed from the targetby vaporization.

A crated is formed. The adjacent area isthermally affected resulting cracks anddebris.

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h = Eg - linear absorption

Nx h = Eg - nonlinear absorption

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Interaction of materials with intense laser beam

Long laser pulses (ns) Ultrashort laser pulses (fs)

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Laser processing with ns pulses Laser processing with fs pulses

Long pulses: The heat affected zone is much larger than the laser irradiated area.

Nanosecond versus femtosecond laser processing

Short pulses: nonlinear absorption in the center of a focalized beam inducesmaterial modification at submicrometer size => micro and nanostructuring

800 nm

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How to overcome the diffraction limit by a femtosecond laser?

Focused fslaser beam

GeneratedStructure

Threshold

3D translation

Femtosecond laser beameasily induces nonlinearabsorption in the centerof a focused spot.

UV

NIR fs

NIR2

NIR two-photon vs. UV absorption

photochemical reaction (photopolymerization)

glass densification (waveguide in glasses) laser ablation

Two-photons or multiphotons absorption:

UV

VB

CB

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When the laser fluence (intensity) is kept

just above the ablation threshold the

material will be processed with precision

under the diffraction limit.

)/ln(2

)(0

thFF

d

Fd

0 5 10 15

0.5

1

1.5

2

2.5

F/Fth

d(m)

d0 = 2 m

NANA

Md

2

0

2

d0 minimum diameter of the focused

laser beam

NA numerical aperture

Laser spot diameter vs ablated spot

1/e2

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OperatorLaser monitoring

LDW microscope

Femtosecondlaser

Laser Direct-Writing (LDW) with femtosecond laser

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Opto-mechanical system for micro/nano-structuring

Focusing optics- 10X to 100X- NA from 0.2 to 1.4 (immersion oil).

Translation system XYZ- stepper: 4x4x4 mm3 or 50x50x25 mm3.

- precision 400 nm.- piezo: 20x20x20 m3

Visualization- CCD camera 768 x 494 pixels.- image rezolution < 1 m

Laser sources- Clark MXR - CPA2101:

wavelength 775 nm ,pulse duration 200 fs,repetition rate 2KHz ;

- Femtolasers Synergy Pro:790 nm, 20 fs, 75 MHz .

- Specta Physics Tsunami:

750-850 nm, 80 fs, 80MHz ;

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Microstructures fabricated by femtosecond laser ablation

Laser ablation of alumina target(100 m thickness)

200 m

50 m

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Laser ablated holes on gold film 100 nm.Diameter ~ 830 nm.

Structures on Co/Cu/Co filmsGrooves width < 500 nm


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100 nm gold thin-film deposited on glass. Structures period of 2 m. Laserwavelength 775 nm, duration 200 fs.

Structures such as interdigital capacitors, electrodes for micro-sensors, etc. canbe produced by laser ablation on metallic films, semiconductors, or ceramicsusually difficult to be processed by chemical etching.


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Interdigital capacitors fabricated by femtosecond laser

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Microwave devices fabricated by femtosecond laser ablation

Pass-Band Filter Directional coupler

Microwave antenna

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Direct Laser Writing in photopolymers: 3D micro-lithography

10 m

Focused

fs laserbeam

GeneratedStructure

Threshold

3D translation

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Microstructures produced by TPP in photopolymers

Applications :

- Micro-optics components:microlenses, photonic crystals,waveguides, optical couplers;

- OCT calibration samples;

- Biocompatible microstructures;

- Micro-fluidics.

SU-8, ORMOCERs, ORMOSIL, PMMA

F. Jipa et al., J. Optoel. Adv. Mat. 2010.

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Scaffolds for live cells

Applications of 3D TPP in Life Sciences

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Near-field laser lithography on colloidal nanoparticles

700 nm diameter Silica spheres

deposited on glass substrate with anintermediate 50 nm thick gold layer.

The field enhancement at theinterface of a monolayer of

colloidal nanoparticles with a solidsubstrate produces nanoholes bylaser ablation.

M. Ulmeanu et al., J.Appl.Phys. 2009

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Structures obtained by near-field laser ablation

Laser fluence 6 J/cm2

Laser 532 nm, 450 psSpheres dimension: 700 nm

Structure dimension : ~110 nm

Glass substrate

Laser fluence 0.5 J/cm2

Laser 532 nm, 450 psSpheres dimension: 3 mStructure dimension : ~350 nm

Gold Film 50 nm

1 m

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Parallel processing of photopolymers using colloidal particles

9.468

Spheres of polystyrene (1.5 m diameter) are deposited of SU-8 thin film.

The monolayer of PS spheres areirradiated by fs laser beam.

TPP occurs in optical near-filedenhancement regime.

Numerical FDTD simulation showsan optical field enhancement with afactor of 9.

3 m

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Acceptor Film

Donor film

d

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Two-Photon Excitation Spectroscopy

In the confocal configuration, the DLW workstation is connected through anoptical fiber to a spectrometer. A 100 m optical fiber gives about 5 m lateral

resolution on the sample.

By scanning the samplesurface the TPE microscopyimage can be recorded.

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Set-up for TPE-Spectroscopy

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Typical TPE-PL spectra

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TPE Microscopy work in progress

Reconstructedimages of abiological sample at differentdepths inside the sample.

By scanning the sample in XY, a map ofTPE-PL intensity can be recorded.

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A laser direct writing system was configured for laser processingwith femtosecond laser pulses.

The laser set-up is compatible with laser processing andcharacterisation techniques, such as laser ablation, near-fieldlithography, LIFT, TPP, TPE Spectroscopy.

The system allows us to obtain 2D and 3D structures withsubmicrometric precision.

The obtained structures have applications for micro-sensors, micro-optics, metamaterials, micro-fluidics, etc.

Conclusions

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Thank you for your attention!

http://ssll.inflpr.ro/

Solid State Lasers Group

This work is supported by National Agency of Scientific Research trough the projects:CNCSIS IDEI268, FEMAT, METALASER, FOTOPOL
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