1. LASER DAMAGE - A BALANCED VIEW
Difficult to take the long considered and balanced view when your work stops dead with that flash of light or “ping”
Rona Belford

2. We would like to thank Sean Kudesia for his continued support and useful insights in our LIDT research work and to SELEX ES for its support
Thanks also to Scottish Enterprise for funding our most recent research project

3. To cause damage we need to break bonds
DEFINITION OF LASER DAMAGE
Any permanent laser-radiation-induced change in characteristics of either the Substrate or the Coating
To cause damage we need to break bonds
Permanent Change means alteration in the morphology has occurred and that means a massive change at the molecular level which has its origin in the breaking of bonds
What bonds? and how much energy will it take?

4. Band Diagram for a Crystalline Semiconductor/ InsulatorAO MO
MO*
Increasing Electron Energy
Increasing Electron Energy
Conduction Band Edge
Valence Band Edge
N atoms

5. SiO2 Si 8.9 eV 1.1 eV Increasing Electron Energy Insulator
Semiconductor
Conduction Band Edge
8.9 eV
Increasing Electron Energy
1.1 eV
Valence Band Edge

6. Si

7. We are dealing with Amorphous materials (Glasses) are formed by cooling from the liquid phase melt or by sputtering. The thermal history determines the material’s structure
Structure determines electronic states; thermal history “freezes in” these states

8. Typical Distribution of Electronic States in an Amorphous SC/insulator
Localized States
Tail States
Defect States
Typical Distribution of Electronic States in a Crystalline SC/insulator
Crystalline SiO2
Typical Distribution of Electronic States in an Amorphous SC/insulator
Amorphous SiO2
Structure determines electronic states Annealing differences
Optical glasses have much reduced defect states

9. Origin of these Additional Energy States
The Structure (Amorphous =lack of Periodicity) Dictates the Electronic Structure
“Freezing-in” non-equilibrium features such as bond angle or bond length give states of higher energy bonding electrons and lower energy anti-bonding states

10. Typical Distribution of Electronic States in an Amorphous SC/insulator
Localized States
Tail States
Defect States
Typical Distribution of Electronic States in a Crystalline SC/insulator
Crystalline SiO2
Typical Distribution of Electronic States in an Amorphous SC/insulator
Amorphous SiO2
Structure determines electronic states Annealing differences
Optical glasses have much reduced defect states

11. Free H2O (highly Hydrogen bonded) Modes of Absorbing IR Through Vibration
Symmetric Stretch
Asymmetric Stretch
Deformation (bend)

13. ≡ Si- O H + H O-Si ≡ Elevated Temp ≡ Si-O-Si ≡ +H20

15. BAND STRUCTURE FOR LITHIUM NIOBATE

16. http://phys.strath.ac.uk/12-370/sld006.htm Allister Ferguson

17. http://phys.strath.ac.uk/12-370/sld006.htm Allister Ferguson

18. http://phys.strath.ac.uk/12-370/sld006.htm Allister Ferguson

19. BELFORD RESEARCH FOR ALL YOUR LIDT NEEDS