Sensor fusion and novel “multi-image” systems that have several different spectral ranges are proliferating in tactical and commercial applications. Calibrating these devices requires a variety of sources from quartz-tungsten halogen to blackbodies to more selectable band sources such as LEDs. Usually these sources are used independently in discrete spectral regions, but real reflective and emissive targets often have signatures that make combining these sources necessary if one is to emulate these real spectrums for testing in either image (collimator) or flood (sphere) configurations. A novel approach to combine LED and broadband emitters has been developed to effect stable, calibrated, traceable sources that can match real target spectral signatures.
We report the preliminary characterization results of a gold-coated concentrator used for longwave irradiance
measurements. Throughput measurements of the concentrator are conducted at 1.562 μm and 10.15 μm using two
different approaches, one is referred to a transmittance measurement using the Complete Hemispherical Infrared Laserbased
Reflectometer (CHILR) of NIST, and the other one is a direct throughput measurement using an existing
thermopile detector for longwave irradiance measurement. For the transmittance measurement using CHILR, two diffuse
gold references are selected to generate a Lambertian source by shining a laser on them. Spatial variations of
transmittance of the concentrator are also investigated by scanning the laser beam across the opening area of it with a
gold diffuser. For the direct throughput measurement, a small diffuse gold integrating sphere of 25.4 mm in diameter is
utilized to produce an ideal diffuse source. The thermopile detector measures the radiation passing through the
concentrator from the small integrating sphere. The incoming irradiance is determined from signal outputs of the
thermopile detector and ambient temperature changes. Comparing with the results from the two approaches, a consistent
throughput of the concentrator is obtained about 91 % to 92 %. The error sources and uncertainty in the two
measurements are also discussed.
The optical system discusses is an integrating sphere based uniform source. The system consists of an integrating sphere illuminated with a tungsten halogen lamp system. The output of the integrating sphere is projected using a large single- element collimating lens. Such a system is advantageous in the testing of optical detectors since in a specific region of the projected beam the irradiance is constant in a volume around the optical axis and for a significant distance along the optical axis. This property eases the positioning requirements of devices under test relative to the lens. Relative irradiance predictions of a plane in the collimated beam made using ZEMAX Optical Design Program are presented. Measured data of the relative irradiance in this specific plane achieved with the implemented optical system are presented. Comparison between the predictions and measured data are made. Predictions agreed with the measured data to within 5%.