A Novel Airborne Molecular Contaminants Sensor Based on Sagnac Microfiber Structure

Area of Science:

• Optics and Photonics
• Materials Science
• Laser Technology

Background:

• Airborne molecular contaminants (AMCs) degrade fused silica optics in high power lasers (HPLs).
• Effective monitoring of AMCs is essential for maintaining HPL system performance and optic longevity.
• Existing monitoring methods may lack the sensitivity or real-time capability required for HPL environments.

Purpose of the Study:

• To develop and demonstrate an on-line monitoring method for AMCs concentration using a Sagnac microfiber structure.
• To assess the sensor's sensitivity and feasibility for detecting trace contaminants in vacuum environments.

Main Methods:

• Fabrication of a Sagnac microfiber loop with a mesoporous silica coating using microheater brushing and dip coating.
• Utilizing the change in refractive index due to AMC absorption in the coating to induce spectral shifts.
• Monitoring spectral shifts to quantify AMC concentration and evaluating sensor performance with low-volatilization greases in a vacuum.

Main Results:

• The Sagnac microfiber sensor demonstrated on-line monitoring of AMCs concentration.
• The sensor achieved a sensitivity of 0.11 nm/(mg/m³).
• Feasibility was confirmed by evaluating gas discharge characteristics of greases in a vacuum, showing promise for detecting trace contaminants.

Conclusions:

• The proposed Sagnac microfiber sensor is a promising tool for on-line detection of AMCs.
• This technology can help meet the stringent requirements for monitoring trace contaminants in HPL systems.
• Real-time AMC monitoring can contribute to extending the lifetime of critical optical components.