Loss in long-storage-time optical cavities

Area of Science:

• Optical Physics
• Metrology
• Experimental Physics

Background:

• Fabry-Perot cavities are essential for precision measurements.
• Optical loss in these cavities significantly impacts experimental performance.
• Characterizing mirror loss independently is challenging.

Purpose of the Study:

• To directly measure optical loss in situ within a long-storage-time Fabry-Perot cavity.
• To investigate the dependence of optical loss on beam spot size and position.
• To provide data relevant for gravitational-wave interferometers.

Main Methods:

• Application of three in situ optical loss measurement techniques.
• Utilizing a high-finesse, near-concentric, 2 m Fabry-Perot cavity.
• Modifying cavity length to vary beam spot size (1-3 mm) and observing loss.

Main Results:

• Optical loss was found to be approximately 5 parts per million (ppm) per mirror.
• Optical loss showed a stronger dependence on the position of the beam spot on the optics than on its size.
• Loss remained relatively constant across the tested beam spot size range.

Conclusions:

• Direct in situ measurement of optical loss is feasible and valuable.
• Beam spot positioning is a critical factor for minimizing optical loss in Fabry-Perot cavities.
• Findings have direct implications for improving squeezed light applications in gravitational-wave detectors.