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Primary optical watt radiometer (POWR) facility


POWR is a cryogenic electrical substitution radiometer that serves as the Nation's optical power reference.

Specifications / Capabilities:

  • Dynamic range of primary standard power levels, 0.01 % at 1 mW to 1 mW).
  • Periodic shuttering with active cavity, feed-forward, and phase-sensitive detection.
  • Optional 2-Kelvin operational temperature mode for greater sensitivity compared with the standard 4.2-Kelvin operational temperature.
  • Continuous spectral coverage possible at the primary standard using tunable lasers from the adjacent SIRCUS facilities.
  • Extended IR coverage and UV coverage using the primary standard.
  • Possibility for windowless transfer from the primary standard, decreasing transfer uncertainties.
  • Horizontal optical path eliminates the need for turning mirror, and provides more space for larger transfer detectors to be calibrated.
  • Beyond radiant power, irradiance measurements using the POWR facility are conceivable.
  • Captures future, unknown primary standard requirements through modular design.
  • 2-weeks between liquid helium transfers, even when operating at 2 K temperature.

Internal intercomparison:

Optical power measurements on POWR were compared with two other absolute cryogenic radiometers at NIST:

  1. LOCR (Laser-Optimized Cryogenic Radiometer) located in NIST Boulder.
  2. A portable ACR located in the NIST SIRCUS facility.

The spectral power responsivity of two trap detectors measured at 488 nm, 514 nm, and 633 nm with the two cryogenic radiometers agreed to within ±0.02 %, comparable to the uncertainties of these radiometers.

Schematic of the POWR instrument

Name: Ping-Shine Shaw
Phone: 301-975-4416
Email: ping-shine.shaw@nist.gov
100 Bureau Drive, M/S 8444
Gaithersburg, MD 20899-8444

Name: Steven Brown
Phone: 301-975-5167
Email: steven.brown@nist.gov

Name: John Woodward
Phone: 301-975-5495
Email: john.woodward@nist.gov

Name: Keith Lykke
Phone: 301-975-3216
Email: keith.lykke@nist.gov