Spectral radiance source based on supercontinuum laser and wavelength tunable bandpass filter: the spectrally tunable absolute irradiance and radiance source

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 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.

Contributed Review: Absolute spectral radiance calibration of fiber-optic shock-temperature pyrometers using a coiled-coil irradiance standard lamp

“…The modern alternatives to these relatively cheap yet robust and reliable light sources are standards of spectral radiance employing integrating spheres 65,66 and high-power quartz halogen lamps or quasi-continuouswave lasers. These devices provide superior light uniformity over large exit aperture areas, up to 100 mm in diameter.…”

MODIS and VIIRS Calibration History and Future Outlook

“…The tunable, intensity stabilized laser approach described in Section 3 moves SI traceability of radiometric calibration from the SIS-100 source-based system to a reference trap detector-based system while producing lower overall calibration uncertainties. For the calibration of absolute spectral radiance responsivities of remote sensing instruments, systems incorporating supercontinuum (i.e., white light) laser sources (SLS) with laser line tunable filters (LLTF) are being developed [51,52]. In these systems, the intensity stabilized, monochromatic output of a tunable supercontinuum laser with LLTF is input to an integrating sphere whose output is monitored using trap reference detectors calibrated for absolute spectral radiance responsivity.…”

Implication of Illumination Beam Geometry on Stray Light and Bandpass Characteristics of Diode Array Spectrometer

“…The MMS 1 spectrometer module (NIR enhanced variant), FEE-HS front-end electronics, and interface electronics used in this study are components of the SkySpec B hyperspectral radiometer described in [17]. As mentioned, the LSFs were measured with a spectrally tunable absolute irradiance and radiance source (STAIRS) [18] and verified with a double monochromator setup.…”