CCD based spectrometers are commonly used to characterize the optical performance of LEDs. All CCD based spectrometers exhibit varying amounts of stray light. This situation is exacerbated by using tungsten-halogen based sources for calibration. NIST has come up with methods to characterize the stray light associated with CCD based spectrometers using multiple lasers spanning the visible and near IR spectrum. At Sphereoptics we have developed methods to map out and correct for stray light using a double monochromator and software. We have been able to mathematically remove the effects of stray light on many common LED characterization measurements such as spectral flux for instance. These effects were found to be quite substantial especially in the UV part of the spectrum. In this paper we will present our findings on the nature of stray light found in a B&W BRC112E UV spectrometer as well as our progress in correcting the errors it causes.
Integrating spheres for optical calibration of remote sensing cameras have traditionally been made with Quartz Tungsten Halogen (QTH) lamps because of their stability. However, QTH lamps have the spectrum of a blackbody at approximately 3000K, while remote sensing cameras are designed to view a sun-illuminated scene. This presents a severe significant mismatch in the blue end of the spectrum. Attempts to compensate for this spectral mismatch have primarily used Xenon lamps to augment the QTH lamps. However, Xenon lamps suffer from temporal instability that is not desirable in many applications. This paper investigates the possibility of using RF-excited plasma lamps to augment QTH lamps. These plasma lamps have a somewhat smoother spectrum than Xenon. Like Xenon, they have more fluctuation than QTH lamps, but the fluctuations are slower and may be able to be tracked in an actual OGSE light source. The paper presents measurements of spectra and stability. The spectrum is measured from 320 nm to 2500 nm and the temporal stability from DC to 10 MHz. The RF-excited plasma lamps are quite small, less than 10mm in diameter and about 15 mm in length. This makes them suitable for designing reasonably sized reflective optics for directing their light into a small port on an integrating sphere. The concludes with a roadmap for further testing.
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