Intercomparison of the LBIR Absolute Cryogenic Radiometers to the NIST Optical Power Measurement Standard

Area of Science:

• Metrology and Measurement Science
• Optical Physics and Infrared Technology

Background:

• The Low Background Infrared (LBIR) calibration facility at NIST utilizes four absolute cryogenic radiometers (ACRs) as standard reference detectors.
• The High Accuracy Cryogenic Radiometer (HACR) was the previous primary standard for optical power at NIST, now succeeded by the Primary Optical Watt Radiometer (POWR).

Purpose of the Study:

• To compare the radiometric power measurements of the four LBIR facility ACRs against NIST's primary standards (HACR and POWR).
• To validate the accuracy and consistency of the ACRs used in infrared calibrations.

Main Methods:

• A silicon photodiode light-trapping detector was employed as a secondary transfer standard.
• Detailed methodology for comparing each ACR to the trap detector was implemented.
• Radiometric power measurements were conducted using the primary standards and the ACRs via the transfer standard.

Main Results:

• All four absolute cryogenic radiometers (ACRs) demonstrated agreement with the primary standards.
• The absolute optical power measurements from the ACRs were found to be within 0.1% of the primary standard.
• Successful intercomparison between national primary standards and facility ACRs was achieved.

Conclusions:

• The LBIR facility's ACRs are highly accurate and reliable for infrared calibrations.
• The established comparison technique using a silicon photodiode trap detector is effective for validating radiometer performance.
• Measurement results confirm the high metrological capability of NIST's infrared calibration standards.