1 / 27

Femtosecond laser ablation dynamics in wide band gap crystals.

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.

ulfah
Download Presentation

Femtosecond laser ablation dynamics in wide band gap crystals.

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Femtosecond laser ablation dynamics in wide band gap crystals. N.Fedorov CEA/DSM/IRAMIS École Polytechnique

  2. 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.

  3. 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.

  4. Metal Laser crater plasma Femtosecond laser’s applications for micromachining. Problem: Micro channels high profundity Condensation of vaporized material on channel border. • Detection in non-transparent material (metal): • Crater profile • Plasma light emission • Electron / Ion emission. • Light reflection modulation

  5. Dielectric Crystal plasma Laser Luminescence emission Plasma emission Femtosecond laser’s applications for micromachining. Why scintillation crystals? • Plasma emission • Induced absorption • Reflection modulation. • Self emission. • Refraction index modulation. Plasma Electronic excitations in dielectric Possible to study density of electronic excitation inside the sample. Scintillation crystals: SiO2:H, CdWO4,ets.

  6. Single pulse surface modification Quartz monocrystal, Irradiation by SLIC Ti:Saphire laser at CEA/Saclay 50fs 800nm 20Hz repetition rateor second harmonic (400nm) Surfase modifications in crater: • Periodic structure • “Mouldy” surface: nanofibers.

  7. 400nm 5J/cm2 (1014W/cm2) Single shot Nano-particles and nano-fibers • Fast cooling of plasma. • Collapsing to drops. • Drop of glass stretch a fiber.

  8. 400nm 5J/cm2 (1014W/cm2) Single shot

  9. Periodic structure in the crater • Evolution of structure with number of shots • Direction of the structure and polarization. • Polarization • Exposition.

  10. 400nm 5J/cm2 (1014W/cm2) 1 shot

  11. 400nm 5J/cm2 (1014W/cm2) 5 shots

  12. 400nm 5J/cm2 (1014W/cm2) 10 shots

  13. 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. SEM image brightness amplitude Period 800nm Fitting by Sin6 AFM measurement is required.

  14. Polarization. • Literature: Structure is parallel to polarization • 400nm: Structure is parallel to polarization • 800nm: Structure is perpendicular to polarization 400nm 800nm

  15. Polarization. Verification of polarization. • Vertical – horizontal • Horizontal – vertical • Circular-circular. 800nm circular polarization 800nm 800nm

  16. Polarization. 800nm Long exposition (50J/cm2 x 20Hz : 1015W/cm2) : Appearance of parallel structure. 800nm

  17. Polarization, picosecond pulse duration. 800nm Long exposition (40J/cm2 : 2*1013W/cm2) pulse duration 2ps: Appearance of parallel structure. 800nm

  18. Different pulse durations. • Femtoseconds (50fs) • Excitation of electrons. • Absorption of laser pulse by electrons • Vaporization All processes on the surface • Picoseconds (2ps) • Amorphization • Darkening • Absorption by amorphous dark volume Heating of big volume.

  19. 800nm 40J/cm2 (1013W/cm2) 1 shot Very weak modification

  20. 800nm 40J/cm2 (1013W/cm2) 5 shots Parallel and perpendicular structures.

  21. 800nm 40J/cm2 (1013W/cm2) 10 shots Dark spot in the center

  22. 800nm 40J/cm2 (1013W/cm2) 12 shots Beginning of boiling in the center

  23. 800nm 40J/cm2 (1013W/cm2) 15 shots Boiling in the center

  24. 800nm 40J/cm2 (1013W/cm2) 20 shots Boiling all the crater.

  25. 800nm 40J/cm2 (1013W/cm2) multi shots Cracks around crater Strong heating in the volume under surfase

  26. 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.

  27. 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

More Related