Ion-beam-sputtered mid-infrared coatings for hybrid supermirrors

Area of Science:

• Materials Science
• Optics
• Thin Film Technology

Background:

• Supermirrors are crucial optical components requiring highly reflective, low-loss coatings.
• Mid-infrared (MIR) applications demand specialized coatings that are challenging to develop.
• Previous work established foundational results for MIR coatings.

Purpose of the Study:

• To develop novel low-loss ion-beam-sputtered (IBS) coatings for hybrid supermirrors in the mid-infrared spectrum.
• To investigate the use of amorphous silicon (a-Si) as a direct bonding layer for enhanced performance.
• To achieve high reflectivity and low optical loss for advanced MIR optical systems.

Main Methods:

• Fabrication of two distinct dielectric Bragg reflector (DBR) designs (HR1 and HR2) using IBS deposition.
• Integration of IBS coatings with crystalline mirrors (GaAs/AlGaAs) to create hybrid supermirrors.
• Characterization of optical performance, including total loss, excess loss, and cavity finesse at 4.45 µm.

Main Results:

• Achieved low total loss (9.3 ppm) and excess loss (6.8 ppm) at 4.45 µm using HR2-based hybrid supermirrors.
• Demonstrated a maximum cavity finesse of 396,000.
• Verified sub-angstrom roughness for IBS-deposited a-Si used directly as a bonding layer, a novel approach.

Conclusions:

• The developed IBS coatings offer excellent optical performance for mid-infrared hybrid supermirrors.
• The direct use of a-Si as a bonding layer is validated, showing sub-angstrom roughness and superior optical properties.
• This work provides a scalable pathway for advanced coatings in longer mid-infrared wavelengths.