Photothermal deflection in multilayer coatings: modeling and experiment

Area of Science:

• Materials Science
• Optical Engineering
• Physics

Background:

• Accurate characterization of optical coatings is essential for high-performance optical systems.
• Understanding absorption in multilayer dielectric coatings is critical for preventing damage and optimizing performance, especially in high-power applications.
• Existing methods for measuring low absorption in thin films can be limited in sensitivity and scope.

Purpose of the Study:

• To develop and validate a comprehensive model for the photothermal deflection signal in multilayer coatings.
• To incorporate optical interference effects and heat flow dynamics into the photothermal deflection model.
• To enable highly sensitive and accurate measurement of absorption in ultraviolet (UV) dielectric mirrors.

Main Methods:

• Development of a theoretical model for photothermal deflection signal considering optical interference and thermal transport within multilayer stacks.
• Fabrication of high-reflectivity HfO2/SiO2 UV mirrors using plasma ion assisted deposition.
• Experimental measurement of photothermal deflection signals from fabricated mirrors.
• Comparison of experimental data with theoretical calculations from the developed model.

Main Results:

• The developed photothermal deflection model accurately predicts the signal by accounting for optical interference and heat flow.
• Experimental measurements of HfO2/SiO2 UV mirrors showed good agreement with the model's predictions.
• The validated model and experimental setup allow for the measurement of absorption as low as 10^-7 of incident power.

Conclusions:

• The presented photothermal deflection model provides a robust framework for analyzing multilayer optical coatings.
• The model's accuracy is confirmed by experimental validation on HfO2/SiO2 UV mirrors.
• This approach offers a highly sensitive method for quantifying absorption in optical thin films, vital for advanced optical applications.