Abstract

A new spectrally tunable source for calibration of radiometric detectors in radiance, irradiance, or power mode has been developed and characterized. It is termed the spectrally tunable absolute irradiance and radiance source (STAIRS). It consists of a supercontinuum laser, wavelength tunable bandpass filter, power stabilization feedback control scheme, and output coupling optics. It has the advantages of relative portability and a collimated beam (low étendue), and is an alternative to conventional sources such as tungsten lamps, blackbodies, or tunable lasers. The supercontinuum laser is a commercial Fianium SC400-6-02, which has a wavelength range between 400 and 2500 nm and a total power of 6 W. The wavelength tunable bandpass filter, a PhotonEtc laser line tunable filter (LLTF), is tunable between 400 and 1000 nm and has a bandwidth of 1 or 2 nm depending on the wavelength selected. The collimated laser beam from the LLTF filter is converted to an appropriate spatial and angular distribution for the application considered (i.e., for radiance, irradiance, or power mode calibration of a radiometric sensor) with the output coupling optics, for example, an integrating sphere, and the spectral radiance/irradiance/power of the source is measured using a calibration optical sensor. A power stabilization feedback control scheme has been incorporated that stabilizes the source to better than 0.01% for averaging times longer than 100 s. The out-of-band transmission of the LLTF filter is estimated to be $<-65\mathrm{dB}$ (0.00003%), and is sufficiently low for many end-user applications, for example the spectral radiance calibration of earth observation imaging radiometers and the stray light characterization of array spectrometers (the end-user optical sensor). We have made initial measurements of two end-user instruments with the STAIRS source, an array spectrometer and ocean color radiometer.

Facility for spectral irradiance and radiance responsivity calibrations using uniform sources

Steven W. Brown, George P. Eppeldauer, and Keith R. Lykke
Appl. Opt. 45(32) 8218-8237 (2006)

Absolute detector-based spectrally tunable radiant source using digital micromirror device and supercontinuum fiber laser

Zhigang Li, Xiaoxu Wang, Yuquan Zheng, and Futian Li
Appl. Opt. 56(17) 5073-5079 (2017)

Comparison of absolute spectral irradiance responsivity measurement techniques using wavelength-tunable lasers

Ville Ahtee, Steven W. Brown, Thomas C. Larason, Keith R. Lykke, Erkki Ikonen, and Mart Noorma
Appl. Opt. 46(20) 4228-4236 (2007)

Validation of short-pulse-laser-based measurement setup for absolute spectral irradiance responsivity calibration

Michaela Schuster, Saulius Nevas, and Armin Sperling
Appl. Opt. 53(13) 2815-2821 (2014)

Pyroelectric detector-based method for low uncertainty spectral irradiance and radiance responsivity calibrations in the infrared using tunable lasers

Brian G. Alberding, John T. Woodward, Ping-Shine Shaw, Leonard M. Hanssen, Catherine C. Cooksey, and Joseph P. Rice
Appl. Opt. 61(11) 2957-2966 (2022)