femtosecond laser ablation dynamics in wide band gap crystals
DESCRIPTION
Femtosecond laser ablation dynamics in wide band gap crystals. N.Fedorov CEA/DSM/IRAMIS École Polytechnique. Summary. Introduction. Problems of micro-machining Proposed experiments. Femtosecond ablation Single shot surface modification. Multi shot surface modification. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Femtosecond laser ablation dynamics in wide band gap crystals](https://reader035.vdocuments.mx/reader035/viewer/2022062409/568151bc550346895dbfee6d/html5/thumbnails/1.jpg)
Femtosecond laser ablation dynamics in wide band gap
crystals.
N.FedorovCEA/DSM/IRAMIS
École Polytechnique
![Page 2: Femtosecond laser ablation dynamics in wide band gap crystals](https://reader035.vdocuments.mx/reader035/viewer/2022062409/568151bc550346895dbfee6d/html5/thumbnails/2.jpg)
Summary
• Introduction.– Problems of micro-machining– Proposed experiments.
• Femtosecond ablation– Single shot surface modification.– Multi shot surface modification.
• Ablation under picosecond pulse.
• Conclusion and perspectives.
![Page 3: Femtosecond laser ablation dynamics in wide band gap crystals](https://reader035.vdocuments.mx/reader035/viewer/2022062409/568151bc550346895dbfee6d/html5/thumbnails/3.jpg)
Material Ejection
Stages of ablation for dielectric crystal• Excitation of electrons
• Heating of electrons by laser.
• Heating of surface.
• Vaporization.
• Cooling and condensation of material.
![Page 4: Femtosecond laser ablation dynamics in wide band gap crystals](https://reader035.vdocuments.mx/reader035/viewer/2022062409/568151bc550346895dbfee6d/html5/thumbnails/4.jpg)
Femtosecond laser’s applications for micromachining.
Problem: Micro channels high profundityCondensation of vaporized material on channel border.
Detection in non-transparent material (metal):
•Crater profile
•Plasma light emission
•Electron / Ion emission.
•Light reflection modulation
craterLaser
Metal
plasma
![Page 5: Femtosecond laser ablation dynamics in wide band gap crystals](https://reader035.vdocuments.mx/reader035/viewer/2022062409/568151bc550346895dbfee6d/html5/thumbnails/5.jpg)
Femtosecond laser’s applications for micromachining.
Why scintillation crystals?• Plasma emission• Induced absorption• Reflection modulation.• Self emission.• Refraction index modulation.
Possible to study density of electronic excitation inside the sample.
Plasma
Electronic excitations in dielectric
Laser
Dielectric Crystalplasma
Plasma emission
Luminescence emission
Scintillation crystals:
SiO2:H, CdWO4,ets.
![Page 6: Femtosecond laser ablation dynamics in wide band gap crystals](https://reader035.vdocuments.mx/reader035/viewer/2022062409/568151bc550346895dbfee6d/html5/thumbnails/6.jpg)
Single pulse surface modification
Surfase modifications in
crater:• Periodic structure• “Mouldy” surface:
nanofibers.
Quartz monocrystal,
Irradiation by SLIC Ti:Saphire laser at CEA/Saclay 50fs 800nm 20Hz repetition rate or second harmonic (400nm)
![Page 7: Femtosecond laser ablation dynamics in wide band gap crystals](https://reader035.vdocuments.mx/reader035/viewer/2022062409/568151bc550346895dbfee6d/html5/thumbnails/7.jpg)
Nano-particles and nano-fibers
• Fast cooling of plasma.• Collapsing to drops.• Drop of glass stretch a fiber.
400nm 5J/cm2 (1014W/cm2) Single shot
![Page 8: Femtosecond laser ablation dynamics in wide band gap crystals](https://reader035.vdocuments.mx/reader035/viewer/2022062409/568151bc550346895dbfee6d/html5/thumbnails/8.jpg)
400nm 5J/cm2 (1014W/cm2) Single shot
![Page 9: Femtosecond laser ablation dynamics in wide band gap crystals](https://reader035.vdocuments.mx/reader035/viewer/2022062409/568151bc550346895dbfee6d/html5/thumbnails/9.jpg)
Periodic structure in the crater
• Evolution of structure with number of shots
• Direction of the structure and polarization.– Polarization– Exposition.
![Page 10: Femtosecond laser ablation dynamics in wide band gap crystals](https://reader035.vdocuments.mx/reader035/viewer/2022062409/568151bc550346895dbfee6d/html5/thumbnails/10.jpg)
400nm 5J/cm2 (1014W/cm2) 1 shot
![Page 11: Femtosecond laser ablation dynamics in wide band gap crystals](https://reader035.vdocuments.mx/reader035/viewer/2022062409/568151bc550346895dbfee6d/html5/thumbnails/11.jpg)
400nm 5J/cm2 (1014W/cm2) 5 shots
![Page 12: Femtosecond laser ablation dynamics in wide band gap crystals](https://reader035.vdocuments.mx/reader035/viewer/2022062409/568151bc550346895dbfee6d/html5/thumbnails/12.jpg)
400nm 5J/cm2 (1014W/cm2) 10 shots
![Page 13: Femtosecond laser ablation dynamics in wide band gap crystals](https://reader035.vdocuments.mx/reader035/viewer/2022062409/568151bc550346895dbfee6d/html5/thumbnails/13.jpg)
Period and amplitude of structure.
• L=l/1+Sin(F)=l normal incidence• Amplitude proportional to Sinn where n is multi
photonic order n=Eg/Eph. For SiO2 Eg=9eV, Ti:Saphire 800nm: Eph=1.55eV
• n(800nm)=6, n(400nm)=3.
200 400 600 800 1000 1200
0 .5
1 .0
1 .5
SEM image brightness amplitude
Period 800nm
Fitting by Sin6
AFM measurement is required.
![Page 14: Femtosecond laser ablation dynamics in wide band gap crystals](https://reader035.vdocuments.mx/reader035/viewer/2022062409/568151bc550346895dbfee6d/html5/thumbnails/14.jpg)
Polarization.
• Literature: Structure is parallel to polarization• 400nm: Structure is parallel to polarization• 800nm: Structure is perpendicular to polarization
400nm
800nm
![Page 15: Femtosecond laser ablation dynamics in wide band gap crystals](https://reader035.vdocuments.mx/reader035/viewer/2022062409/568151bc550346895dbfee6d/html5/thumbnails/15.jpg)
Polarization.
Verification of polarization.• Vertical – horizontal• Horizontal – vertical• Circular-circular.
800nm
800nm circular polarization
800nm
![Page 16: Femtosecond laser ablation dynamics in wide band gap crystals](https://reader035.vdocuments.mx/reader035/viewer/2022062409/568151bc550346895dbfee6d/html5/thumbnails/16.jpg)
Polarization.
800nm Long exposition (50J/cm2 x 20Hz : 1015W/cm2) :
Appearance of parallel structure.
800nm
![Page 17: Femtosecond laser ablation dynamics in wide band gap crystals](https://reader035.vdocuments.mx/reader035/viewer/2022062409/568151bc550346895dbfee6d/html5/thumbnails/17.jpg)
Polarization, picosecond pulse duration.
800nm Long exposition (40J/cm2 : 2*1013W/cm2) pulse duration 2ps:
Appearance of parallel structure.800nm
![Page 18: Femtosecond laser ablation dynamics in wide band gap crystals](https://reader035.vdocuments.mx/reader035/viewer/2022062409/568151bc550346895dbfee6d/html5/thumbnails/18.jpg)
Different pulse durations.
• Femtoseconds (50fs)– Excitation of electrons.– Absorption of laser pulse by electrons– VaporizationAll processes on the surface
• Picoseconds (2ps)– Amorphization– Darkening– Absorption by amorphous dark volumeHeating of big volume.
![Page 19: Femtosecond laser ablation dynamics in wide band gap crystals](https://reader035.vdocuments.mx/reader035/viewer/2022062409/568151bc550346895dbfee6d/html5/thumbnails/19.jpg)
800nm 40J/cm2 (1013W/cm2) 1 shot
Very weak modification
![Page 20: Femtosecond laser ablation dynamics in wide band gap crystals](https://reader035.vdocuments.mx/reader035/viewer/2022062409/568151bc550346895dbfee6d/html5/thumbnails/20.jpg)
800nm 40J/cm2 (1013W/cm2) 5 shots
Parallel and perpendicular structures.
![Page 21: Femtosecond laser ablation dynamics in wide band gap crystals](https://reader035.vdocuments.mx/reader035/viewer/2022062409/568151bc550346895dbfee6d/html5/thumbnails/21.jpg)
800nm 40J/cm2 (1013W/cm2) 10 shots
Dark spot in the center
![Page 22: Femtosecond laser ablation dynamics in wide band gap crystals](https://reader035.vdocuments.mx/reader035/viewer/2022062409/568151bc550346895dbfee6d/html5/thumbnails/22.jpg)
800nm 40J/cm2 (1013W/cm2) 12 shots
Beginning of boiling in the center
![Page 23: Femtosecond laser ablation dynamics in wide band gap crystals](https://reader035.vdocuments.mx/reader035/viewer/2022062409/568151bc550346895dbfee6d/html5/thumbnails/23.jpg)
800nm 40J/cm2 (1013W/cm2) 15 shots
Boiling in the center
![Page 24: Femtosecond laser ablation dynamics in wide band gap crystals](https://reader035.vdocuments.mx/reader035/viewer/2022062409/568151bc550346895dbfee6d/html5/thumbnails/24.jpg)
800nm 40J/cm2 (1013W/cm2) 20 shots
Boiling all the crater.
![Page 25: Femtosecond laser ablation dynamics in wide band gap crystals](https://reader035.vdocuments.mx/reader035/viewer/2022062409/568151bc550346895dbfee6d/html5/thumbnails/25.jpg)
800nm 40J/cm2 (1013W/cm2) multi shots
Cracks around craterStrong heating in the volume under surfase
![Page 26: Femtosecond laser ablation dynamics in wide band gap crystals](https://reader035.vdocuments.mx/reader035/viewer/2022062409/568151bc550346895dbfee6d/html5/thumbnails/26.jpg)
Conclusions.
• Collapsing of plasma to nano-particles.• Stretching of fibers of glass.• In the case of multi photonic absorption creation
of structure perpendicular to light polarization.• Creation of parallel structure after long
exposition or single photon absorption.• Amplitude of structure is proportional to Sin
power coefficient of nonlinearity.• Long pulse duration gives amorphization,
darkening and heating of volume under surface.
![Page 27: Femtosecond laser ablation dynamics in wide band gap crystals](https://reader035.vdocuments.mx/reader035/viewer/2022062409/568151bc550346895dbfee6d/html5/thumbnails/27.jpg)
Perspectives
Electron density distribution study
• AFM study to amplitude of structure in crater.
• Installation of Intensified CCD Camera for luminescence and plasma emission studies.
• Time resolved imaging of plasma reflection
Merci de votre attention