Ultraviolet sensor is immune to direct sunlight

Feb. 1, 1996
A proprietary ultraviolet (UV) bandpass filter renders a UV sensor immune to direct sunlight for wavelengths from 280 nm through the near-infrared.

A proprietary ultraviolet (UV) bandpass filter renders a UV sensor immune to direct sunlight for wavelengths from 280 nm through the near-infrared. Researchers at Ofil Ltd. (Nes Ziona, Israel) created the sensor by integrating the filter with a small side-on photomultiplier tube and a 14 × 4-mm cesium telluride photocathode. Filter blocking ranges from 6 OD in the near-IR region to 12 OD in the visible region, further increasing at UV wavelengths. Transmission peaks at 255 nm, with a bandwidth (FWHM) of 16 nm, independent of angle of incidence.

Sensor responsivity is 4 A/mW at peak transmission. Direct sun generates a background signal of less than 0.25 nA, with a dark current below 0.05 nA. Without collecting optics, the device detected a 0.5-mW/sr signal at 250 m with a 10:1 signal-to-noise ratio. According to researchers Malka Lindner and Shimon Elstein, adding collection optics and using a larger PMT should expand the detection range out to 5 km for signals of 0.1 W/sr or greater. Applications for solar-blind UV detectors include UV radiometry, fire and missile detection, and pollution monitoring.

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