2011 IR&D Annual Report

Measuring Ultraviolet Sensitivity of New Detectors: Capability Development for the NASA Planetary Instrument Definition and Development Program, 15-R8234

Principal Investigators
Michael W. Davis
Thomas G. Greathouse
Kurt D. Retherford
Gregory S. Winters

Inclusive Dates:  06/27/11 – 10/27/11

Background — SwRI has a nearly 20-year history of building ultraviolet spectrographs for NASA sounding rocket and satellite payloads. Every one of these successful instruments contained a core detector consisting of a microchannel plate (MCP) stack operated at high voltages of 4,000 to 5,000 V. The dependence on high voltages means building a custom high-voltage power supply for each instrument, adding undesirable mass, cost and complexity to the design.

A leading manufacturer of astronomical sensors is developing CMOS detectors that are sensitive down to EUV wavelengths without the use of an MCP or high voltage. Their detectors, while still in the prototype stage, have greater than 40 percent sensitivity to light at wavelengths as short as 200 nm. However, this manufacturer lacks the test capability to measure the sensitivity of these CMOS detectors at shorter wavelengths (100 to 200 nm) of high scientific interest to our UV group.

Approach — The main objective of this experiment was to verify the vacuum ultraviolet sensitivity of the silicon detectors. This measurement was made by directing a known intensity of ultraviolet light at discrete wavelengths onto the test detectors and reading out the resulting photocurrent. The sensitivity of the detector to light of the given wavelength was then calculated from the intensity and wavelength of the input light and the active area of the test detector.

Accomplishments — SwRI demonstrated that the detectors are sensitive to UV light at levels ranging from 9 to 22 percent at 1216 Â to 20 to 40 percent at 1600 Â. These detectors meet the initial criteria of 10 percent sensitivity in the vacuum UV for their use in future spaceflight instrument concepts. Indeed, approximately 40 percent sensitivity at 1600 Â greatly exceeded expectations for the potential suitability of these devices for SwRI UV studies. Further development and UV-optimization of these devices are warranted.

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