Abstract
Frequent intercomparisons between radiometric scales are the foundation of low uncertainty, absolute radiometry. However, radiometric scales are typically established by semi-permanent installations such as cryogenic radiometers and blackbody sources that would require substantial cost and effort to temporarily relocate for intercomparisons. These challenges are often circumvented by using transfer standards. Transfer standards are convenient but add to the overall measurement uncertainty and often multiple standards are needed to cover a broad wavelength range.
We present the development of a compact, room temperature standard reference electrical substitution radiometer (ESR). The radiance, irradiance, and power radiometer (RIPR) incorporates a vertically aligned carbon nanotube absorber to provide high sensitivity over a broad spectral range from the ultraviolet to the far infrared (i.e., 0.2 μm to beyond 100 μm) in a single package. The ESR detector in the RIPR provides an SI traceable absolute power scale. With the addition of a calibrated aperture in front of the detector an absolute irradiance scale is realized. Furthermore, inclusion of a second calibrated aperture a fixed distance from the first realizes an absolute radiance scale. The design is compact and easily configured for different radiometric measurements by underfilling or overfilling the detector aperture for power and irradiance measurements, respectively, or by adding a modular optical baffle and second calibrated aperture for radiance measurements. The size of the detector configured for power or irradiance measurements is 64 mm long by 38 mm wide by 20 mm deep. When configured for radiance an additional 215 mm long optical baffle assembly is included.
We have demonstrated a power noise floor of 0.5 nW for a 20 second integration period, which translates to 25 μW m-2 in irradiance for a 5 mm diameter aperture and 0.05 W m-2 sr-1 in radiance for two 5 mm diameter apertures spaced 200 mm apart. We have validated the RIPR power and irradiance scales against the NIST traceable LASP NACR5 reference detector and observe agreement to within 250 ppm in both power and irradiance. We are currently in the process of validating the RIPR radiance scale against LASP blackbody sources.
We intend to fabricate a number of these radiometers to enable frequent, straightforward intercomparisons with established radiometric scales worldwide, as well as provide a service center of standard reference radiometers available to other labs and institutes for instrument calibrations.
A New Broadband, Room Temperature Standard Reference Radiometer for High Accuracy Intercomparison of Radiometric Scales and Instrument Calibration
Frequent intercomparisons between radiometric scales are the foundation of low uncertainty, absolute radiometry. However, radiometric scales are typically established by semi-permanent installations such as cryogenic radiometers and blackbody sources that would require substantial cost and effort to temporarily relocate for intercomparisons. These challenges are often circumvented by using transfer standards. Transfer standards are convenient but add to the overall measurement uncertainty and often multiple standards are needed to cover a broad wavelength range.
We present the development of a compact, room temperature standard reference electrical substitution radiometer (ESR). The radiance, irradiance, and power radiometer (RIPR) incorporates a vertically aligned carbon nanotube absorber to provide high sensitivity over a broad spectral range from the ultraviolet to the far infrared (i.e., 0.2 μm to beyond 100 μm) in a single package. The ESR detector in the RIPR provides an SI traceable absolute power scale. With the addition of a calibrated aperture in front of the detector an absolute irradiance scale is realized. Furthermore, inclusion of a second calibrated aperture a fixed distance from the first realizes an absolute radiance scale. The design is compact and easily configured for different radiometric measurements by underfilling or overfilling the detector aperture for power and irradiance measurements, respectively, or by adding a modular optical baffle and second calibrated aperture for radiance measurements. The size of the detector configured for power or irradiance measurements is 64 mm long by 38 mm wide by 20 mm deep. When configured for radiance an additional 215 mm long optical baffle assembly is included.
We have demonstrated a power noise floor of 0.5 nW for a 20 second integration period, which translates to 25 μW m-2 in irradiance for a 5 mm diameter aperture and 0.05 W m-2 sr-1 in radiance for two 5 mm diameter apertures spaced 200 mm apart. We have validated the RIPR power and irradiance scales against the NIST traceable LASP NACR5 reference detector and observe agreement to within 250 ppm in both power and irradiance. We are currently in the process of validating the RIPR radiance scale against LASP blackbody sources.
We intend to fabricate a number of these radiometers to enable frequent, straightforward intercomparisons with established radiometric scales worldwide, as well as provide a service center of standard reference radiometers available to other labs and institutes for instrument calibrations.