L-1 Standards and Technology, Inc. Primary Standards, Radiometry & Space


The detector calibration system is designed to measure the absolute power responsivity of transfer standard detectors at wavelengths ranging from 370 nm to 2400 nm using the CryoRad III as the reference detector. The CryoRad III is an Absolute Cryogenic Radiometer (ACR) that measures the optical power incident on an absorbing cavity by measuring the equivalent amount of electrical power needed to keep the cavity at a given temperature. The CryoRad III’s absolute power scale comes from its calibrated electrical power measurement and measurements of the cavity absorptance (typically > 0.9999).  The CryoRad III is very accurate (type B uncertainties are approximately 0.01 %, k=2 for laser based measurements at 500 uW), uniform and sensitive to a broad spectrum of light. Its principal use is as a primary standard for calibration of other radiometric detectors, such as silicon trap detectors which are very uniform and stable at room temperature over many years. Such transfer detectors are usually less complex and easier to operate than primary standards and are, by themselves, important parts of calibration systems. The primary purpose of transfer detectors is to transfer radiometric scales to other working detectors, such as pyro-electric detectors and silicon photodiodes.


The detector calibration system consists of three subsystems (see Drawing): the laser system, the monochromator system, and the comparator system. The laser system is used independent of the monochromator system to directly calibrate detectors at a few discrete wavelengths.  L-1 has provided to VNIIOFI the CryoRad III, detector test chamber, and intercomparison chamber and stage.


The radiometer system consists of the CryoRad III and a test chamber into which five detectors can be mounted. Both the CryoRad III and the transfer chamber are connected to an optical window using a flexible Y-shaped bellows which eliminates the need to measure the window transmittance. The comparator stage selectively moves either the CryoRad III or the transfer chamber into the beam path. Light from the monochromator (or laser) is alternately measured by the CryoRad III and a transfer detector inside the transfer chamber


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