Multipass lock-in thermography for the study of optical coating absorption

Area of Science:

• Materials Science
• Optical Engineering
• Laser Physics

Background:

• High-power laser systems demand optical components with minimal light absorption to prevent thermal damage.
• Accurate measurement of low optical absorption is crucial for developing advanced laser technologies.

Purpose of the Study:

• To develop and demonstrate a sensitive method for measuring low optical absorption in materials for high-power lasers.
• To characterize the absorption of various dielectric coatings using an advanced thermographic technique.

Main Methods:

• Utilized lock-in thermography in a multipass configuration to enhance the effective laser power on samples.
• Employed a kW-class ytterbium fiber laser operating at 1.07 µm, achieving effective sample power up to 5 kW.
• Developed a calibration procedure for accurate absorption measurements in the parts-per-million (ppm) range.

Main Results:

• Successfully measured optical absorption in the ppm range for dielectric coatings.
• Demonstrated the effectiveness of the multipass lock-in thermography system for sensitive absorption analysis.
• Characterized single-layer coatings of HfO2, Ta2O5, TiO2, Nb2O5, and SiO2.

Conclusions:

• The developed multipass lock-in thermography system is highly effective for measuring low optical absorption in laser optics.
• The technique provides critical data for selecting and optimizing materials for high-power laser applications.
• Plasma-assisted electron beam deposition is a viable method for producing low-absorption coatings.