Composite reflective/absorptive IR-blocking filters embedded in metamaterial antireflection-coated silicon

Area of Science:

• Physics
• Materials Science
• Optical Engineering

Background:

• Infrared (IR)-blocking filters are essential for managing radiative heat loads in cryogenic systems.
• Optimizing the sensitivity of far-infrared bolometric detectors requires effective IR filtering.

Purpose of the Study:

• To introduce a new IR filter design combining frequency-selective structures and absorptive composites.
• To demonstrate the filter's capability to significantly reduce thermal loading on sensitive instruments.

Main Methods:

• Fabrication of filters using patterned frequency-selective structures on silicon substrates.
• Incorporation of a thin (25-75 μm) absorptive composite layer with powdered reststrahlen materials.
• Integration of a metamaterial antireflection coating to minimize in-band reflections.

Main Results:

• The filter reflects approximately 50% of incident 300 K blackbody radiation.
• Achieved >99.8% blocking of total IR power with negligible thermal gradients.
• Demonstrated excellent low-frequency transmission (<1% absorption below 750 GHz).
• Silicon substrates ensure near-bath temperature for the absorptive filter area.

Conclusions:

• This novel IR filter design effectively minimizes thermal loading in a single stage.
• The filter is compatible with silicon refractive optical elements for integrated applications.
• The technology offers a significant advancement for cryogenic systems and far-IR detection.