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 www.laserdamage.co.uk

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!

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

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

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.

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!

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.

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.

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.

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.

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

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 www.laserdamage.co.uk 10/15