Mid-infrared supermirrors with finesse exceeding 400 000

Area of Science:

• Optics
• Materials Science
• Spectroscopy

Background:

• Optical cavities with low-loss mirrors are crucial for enhancing path length and intensity in trace gas sensing and precision spectroscopy.
• High-performance mirrors exist for visible and near-infrared (NIR) regions, achieving losses below 2 parts per million (ppm) and cavity finesse over 1 million.
• Similar advancements have been limited in the mid-infrared (MIR) spectral region, despite significant scientific interest.

Purpose of the Study:

• To demonstrate a breakthrough in high-performance mid-infrared (MIR) mirrors.
• To enable enhanced optical cavities for MIR spectroscopy and sensing applications.
• To report on novel substrate-transferred single-crystal interference coatings.

Main Methods:

• Fabrication of substrate-transferred single-crystal interference coatings for MIR applications.
• Characterization of mirror performance, including optical losses (scatter and absorption) and cavity finesse.
• Proof-of-concept demonstration in a linear cavity ring-down spectrometer.

Main Results:

• Achieved cavity finesse values ranging from 200,000 to 400,000 near 4.5 µm.
• Reported excess optical losses (scatter and absorption) below 5 ppm.
• Demonstrated the lowest noise-equivalent absorption in a linear cavity ring-down spectrometer normalized by cavity length.

Conclusions:

• The developed MIR mirrors represent a significant advancement in optical coating technology.
• These high-performance MIR mirrors will enable a wider range of applications in various scientific and industrial fields.
• Potential applications include atmospheric science, environmental monitoring, emissions detection, process gas analysis, and biogenic fuel/plastic verification.