Microwave Cavity Coatings for Ammonia Based Frequency Standards

The practical deployment of compact NH₃ frequency standards is constrained by rapid NH₃ loss through wall interactions in the small, sealed, metallic containers suitable for use as compact microwave cavities. For containers with uncoated, non-passivated walls, usable NH₃ lifetimes are measured in days and are significantly too short for practical applications. We are investigating surface coating strategies to reduce NH₃ loss and quantify the resulting improvement by measuring the reduction in microwave absorption over time. We report measured lifetimes for multiple coating types and compare their stability, cavity-to-cavity variability and impact on cavity quality factor and resonant frequency.