Carbon nanotube electrical-substitution cryogenic radiometer: initial results

Area of Science:

• Metrology
• Materials Science
• Cryogenics

Background:

• Conventional cryogenic radiometers are complex and slow for optical power measurements.
• Need for advanced radiometric instruments with improved speed and simplicity.
• Carbon nanotubes offer unique thermal and electrical properties for sensor applications.

Purpose of the Study:

• To fabricate and characterize a carbon nanotube cryogenic radiometer (CNCR) for electrical-substitution optical power measurements.
• To evaluate the CNCR's performance, speed, and wavelength versatility compared to traditional radiometers.

Main Methods:

• Fabrication of a CNCR using vertically aligned multiwall carbon nanotube arrays (VANTAs) as absorber, heater, and thermistor.
• Integration of VANTAs with a micromachined silicon substrate acting as a weak thermal link.
• Characterization at 3.9 K, comparing electrical and fiber-coupled optical power measurements (50 μW to 1.5 mW) at 1550 nm.

Main Results:

• The CNCR demonstrated equivalent responses between electrical and optical power inputs within experimental uncertainty.
• Measurement uncertainty was primarily limited by temperature fluctuations of the cold stage, not the device itself.
• The CNCR is significantly faster and simpler than conventional cryogenic radiometers.

Conclusions:

• The developed CNCR shows promise as a simpler, faster, and more reproducible alternative for optical power metrology.
• Future performance improvements are expected with enhanced temperature stability.
• The reflectance of the VANTA absorber will become the main performance limitation with improved temperature control.