Integrated Electron/Light Sources
The use of stellar objects, such as stars and planets, for calibration and alignment of optical systems is well known. However, the use of stellar objects is often restricted by atmospheric conditions and/or the physical location of the optical system. As requirements for navigation and navigation update systems reach more exquisite accuracy, the stability of optics, and optical detectors come to limit the ultimate accuracy of the whole navigation system. Such systems use characteristic stellar spectra to locate a reference star (or stars) within the system’s field of view and apply the knowledge of the star location in inertial space for navigation during the mission.
Current calibration techniques do not permit pre-flight, in-flight or real-time calibration. The available optical calibration sources such as lamps and blackbody simulators are bulky and can be used only in laboratory conditions. In addition, they require precise adjustments of the total flux, color, and spectral shape, which are accomplished by using extensive hardware in the form of filters, diaphragms, mirrors, lenses and software to perform complicated calculations to calibrate the data. Achievements in the area of SiC- and Si-based avalanche LEDs combined with the new developments in SiC and group III-nitride material growth, characterization, and processing are currently used for development of miniature and reliable integrated broadband optical calibration sources. Avalanche electroluminescence-based LEDs have numerous advantages over lamps and injective LEDs, including unusually broad emission spectrum, lack of spectral dependence on the current, similarity to solar radiation spectrum, high thermal and temporal stability, and miniature size.
The high stability of these devices in a wide temperature range, including cryogenic temperatures and vacuum environments, has been shown in several prototype devices. We have demonstrated class C and class B solar simulators based on the integrated InGaN and Silicon avalanche emissions. IMS is currently in the development stage of a portable super broadband optical emission sources for field and in-flight calibration of stellar photometers and spectrometers.
Pulsed electron beams allow for direct atomic-scale femtosecond to picosecond temporal resolution observation of structures in the condensed and gas phase by diffraction, crystallography, and microscopy. They are widely used in a variety of fields in materials science, chemistry, and biology. Thermionic electron emission from a filament, used to generate the electrons in continuous regime systems, is completely inapplicable for time-resolved systems due to very large turn-on and turn-off electron generation times. The formation of ultra-short electron pulses is currently achieved by illumination of a photocathode material with a pulsed laser beam, thereby generating free electrons by the photoelectric effect. The free electron packet is then accelerated through an electric field and subsequently shaped using an instrument specific combination of pinholes, electrostatic and magnetostatic lenses.
Field emission cathodes provide an alternative approach to electron generation without the heating power needed in filament-based designs. Lasers employed in photoelectric devices are very fast and can be used to achieve pulses in the pico- and femto-second ranges. Current field-emitter cathodes are electron sources, in the form of arrays of micro-fabricated sharp tips. Field emission is used to extract the electrons without heating or illuminating the cathodes.
IMS has developed, fabricated, and tested (see figures below) ultra-fast high-stability high current-density photon-enhanced pulsed planar cold cathodes that are based on avalanche photon/electron emission diodes. These diodes are fabricated from III-Nitride semiconductor materials and are free of the drawbacks described above.
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