Mid-infrared interference coatings with excess optical loss below 10 ppm

Area of Science:

• Materials Science
• Optics
• Nanotechnology

Background:

• Traditional amorphous multilayers produced via physical vapor deposition (PVD) exhibit limitations in optical loss.
• Achieving ultra-low optical loss is critical for high-performance optical resonators and sensitive measurements.

Purpose of the Study:

• To present high-reflectivity substrate-transferred single-crystal GaAs/AlGaAs interference coatings.
• To demonstrate a novel microfabrication process for achieving record-low optical loss.
• To explore the potential of these coatings for mid-infrared applications.

Main Methods:

• Fabrication of single-crystal GaAs/AlGaAs interference coatings using a novel microfabrication process.
• Optical loss characterization using cavity ring-down, transmittance spectroscopy, and direct absorption tests.
• Investigation of polarization-orientation-dependent loss mechanisms.

Main Results:

• Achieved record-low excess optical loss below 10 parts per million (ppm) at a 4.54 micrometer center wavelength.
• Demonstrated reduced scatter loss due to low surface and interfacial roughness.
• Observed a unique polarization-orientation-dependent loss attributed to elastic anisotropy.

Conclusions:

• The novel microfabrication process enables high-performance mirrors with significantly reduced optical loss compared to PVD methods.
• These mirrors are suitable for developing optical resonators with finesse exceeding 100,000 in the mid-infrared.
• Potential applications include high-resolution spectroscopy, laser stabilization, and ultrasensitive light-matter interaction measurements.