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https://www.nist.gov/laboratories/tools-instruments/primary-optical-watt-radiometer-powr-facility

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TOOLS & INSTRUMENTS

# 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:
                    - LOCR (Laser-Optimized Cryogenic Radiometer) located in NIST Boulder.
                    - 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.

Optical / photometry / laser metrologyCalibration services

## Organizations

                          - NIST Headquarters
                            - Laboratory Programs
                              - Physical Measurement Laboratory
                                - Sensor Science Division
                                  - Remote Sensing Group

## Details

## Contact

                    -  Ping-Shine Shaw  ping-shine.shaw@nist.gov      (301) 975-4416   
                    -  Joseph P Rice  joe.rice@nist.gov      (301) 975-2133   

## Related Projects

Primary optical watt radiometer (POWR)

Spectral irradiance and radiance responsivity calibrations using uniform sources (SIRCUS)

## Related Publications

NIST Reference Cryogenic Radiometer Designed for Versatile Performance

### HEADQUARTERS

301-975-2000

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