1. Laser Optics and Laser Industry Support
Optical Coating Qualification & Laser Damage Testing to ISO 21254:2011 Standards
Laser Optics and Laser Industry Support
After-Test Support; giving you more than just a number

2. Definitions
Testing explained
Origins of damage
Kerr Effect
WHAT IS LASER DAMAGE?
“Any permanent laser-radiation-induced change of the characteristics” of the surface or of the bulk of a specimen ….. ISO 21254:2011 When it happens inside a working laser, laser damage is a wrecking ball!

3. COMPONENT OPTICS IS ESSENTIAL FOR LASER MANUFACTURE
Definitions
Testing explained
Origins of damage
Kerr Effect
WHAT IS LIDT?
Laser-Induced Damage Threshold (LIDT) is the “Highest quantity of laser radiation incident upon the optical component for which the extrapolated probability of damage is zero”, as defined by ISO 21254:2011.
LIDT EVALUATION OF
COMPONENT OPTICS IS ESSENTIAL FOR LASER MANUFACTURE

4. WHICH UNIT: ENERGY OR POWER?
Definitions
Testing explained
Origins of damage
Kerr Effect
WHICH UNIT: ENERGY OR POWER?
Peak Power Density (PPD) is the critical quantity causing damage. PPD is measured in MW/cm2. This is the only stand-alone unit.
We are often asked for certification at specific energy without clarification of the pulse duration; this is meaningless. e.g.
10 J/cm2 with pulse duration 10 ns = 1000 MW/cm2
10 J/cm2 with pulse duration 20 ns = 500 MW/cm2
THESE ARE NOT THE SAME!
W = J/s

5. HOW DOES BRL DETERMINE LIDT?
Definitions
Testing explained
Origins of damage
Kerr Effect
HOW DOES BRL DETERMINE LIDT?
We produce a graph of the experimentally obtained damage, showing damage probability as a function of power.
The LIDT is where the slope intersects the axis - probability of damage is zero.
The damage pattern can give substantial information about the coating.

6. Least fluence only gives you a number- and not a very accurate one!
Definitions
Testing explained
Origins of damage
Kerr Effect
LEAST FLUENCE
Another way to determine LIDT is not to graph results but to use the last value at which no damage occurred. This is a quick test. In the case shown here, least fluence would give an LIDT of 650 MW/cm2 instead of 500 MW/cm2. Least fluence is cheaper, but less accurate, sometime far less accurate.
Least fluence only gives you a number and not a very accurate one!

7. HOW IS A TEST PERFORMED? Definitions Testing explained
Origins of damage
Kerr Effect
HOW IS A TEST PERFORMED?
An optic or witness piece of (ideally) 20 mm diameter clear aperture is required for a full LIDT determination.
Increasing peak power
Several sites in a row are exposed to several shots at a single PPD (MW/cm2).
Starting at a minimum, PPD is increased with each new row. Damage events are more frequent as the power increases. This is the most common test; an S-on-1 test (several shots per site).
This pattern is continued until all sites damage, or substrate ablation occurs, whichever comes first.

8. Our LIDT tests include graphical analysis
and “after-test support” as standard.
We regularly perform laser testing certifications to customer-supplied specifications.
We are pleased to discuss testing requirements and suggest cost-saving approaches.

9. WHERE DOES DAMAGE OCCUR?
Definitions
Testing explained
Origins of damage
Kerr Effect
WHERE DOES DAMAGE OCCUR?
Coating surface
Substrate/coating interface
Substrate Bulk
Coating Bulk
Scratches/digs
Areas of poor adhesion
Substrate surface inclusion
Damage is most likely at the substrate/coating interface.
Substrate Bulk
Coating Bulk
In poor quality optics, damage is also due to imperfections such as inclusions, dislocations, or other inhomogeneities. These give rise to a non-standard damage pattern.

10. Good coating- substrate adhesion
Definitions
Testing explained
Origins of damage
Kerr Effect
EXAMPLE OF ADDED VALUE
Poor surface quality
Good coating- substrate adhesion
BRL can give the coater more than a number. For example the graphical analysis above indicates “cosmetic issues” but an essentially good coating/substrate interface.

11. We have an excellent reputation and history of research capability
Coating development benefits from accurate informative LIDT
Come and hear our talk
“Insights into laser-damage testing” by Dr Kieran Mulholland at Photonex in the Optical Engineering & Design session
12th October 2016 Ricoh Arena Coventry
10/15

12. Check us out at www.laserdamage.co.uk
Turnaround - under 3 working days
Accurate and full test reports
Graphical analysis
After test support and discussion
Check us out at
10/15