Dr. Freeman D. Shepherd Profile

Dr. Freeman D. Shepherd

Senior Scientist

SPIE Involvement:

Author

Proceedings Article | 26 August 2010 Paper

Applications of multispectral video

Jim Murguia, Greg Diaz, Toby Reeves, Rick Nelson, Jon Mooney, Freeman Shepherd, Greg Griffith, Darlene Franco

Proceedings Volume 7780, 77800B (2010) https://doi.org/10.1117/12.861631

KEYWORDS: Sensors, Telescopes, Video, Video surveillance, Principal component analysis, Magdalena Ridge Observatory, Space telescopes, Image sensors, Target detection, Astronomical telescopes

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Proceedings Article | 27 August 2008 Paper

Adaptive MWIR spectral imaging sensor

F. Shepherd, J. Mooney, T. Reeves, P. Dumont, M. Weeks, S. DiSalvo

Proceedings Volume 7055, 705506 (2008) https://doi.org/10.1117/12.792761

KEYWORDS: Sensors, Prisms, Image sensors, Mid-IR, Cameras, Imaging spectroscopy, Spectral resolution, Infrared cameras, Monochromators, Image restoration

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Proceedings Article | 12 September 2007 Paper

SWIR variable dispersion spectral imaging sensor

F. Shepherd, J. Mooney, T. Reeves, D. Franco, J. Murguia, C. Wong, P. Dumont, F. Khaghani, G. Diaz, M. Weeks, D. Leahy

Proceedings Volume 6660, 66600J (2007) https://doi.org/10.1117/12.740364

KEYWORDS: Sensors, Prisms, Image sensors, Short wave infrared radiation, Infrared cameras, Imaging spectroscopy, Cameras, Infrared imaging, Image processing, Infrared radiation

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Proceedings Article | 15 December 2000 Paper

Application of Schottky barrier bolometer arrays to cooled sensors

Freeman Shepherd, James Murguia

Proceedings Volume 4130, (2000) https://doi.org/10.1117/12.409850

KEYWORDS: Sensors, Diodes, Thermography, Bolometers, Temperature metrology, Signal to noise ratio, Silicon, Thermal modeling, Thermal sensing, Signal detection

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Proceedings Article | 17 July 2000 Paper

Compact visible/near-infrared hyperspectral imager

James Murguia, Toby Reeves, Jonathan Mooney, William Ewing, Freeman Shepherd, Andrzej Brodzik

Proceedings Volume 4028, (2000) https://doi.org/10.1117/12.391760

KEYWORDS: Sensors, Prisms, Hyperspectral imaging, Image sensors, Cameras, Light emitting diodes, Tomography, Imaging systems, Video, Infrared sensors

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Proceedings Article | 17 July 2000 Paper

Comparison of infrared detection mechanisms in thermal-emissive vs. photoemissive silicon Schottky barrier arrays

Freeman Shepherd, James Murguia

Proceedings Volume 4028, (2000) https://doi.org/10.1117/12.391721

KEYWORDS: Sensors, Diodes, Bolometers, Thermography, Electrodes, Quantum efficiency, Temperature metrology, Silicon, Cameras, Interference (communication)

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Proceedings Article | 26 July 1999 Paper

Performance analysis of a thermionic thermal detector at 400 K, 300 K, and 200 K

James Murguia, Prabha Tedrow, Freeman Shepherd, Darin Leahy, Melanie Weeks

Proceedings Volume 3698, (1999) https://doi.org/10.1117/12.354538

KEYWORDS: Sensors, Diodes, Silicon, Thermography, Optical amplifiers, Signal detection, Multiplexers, Diffusion, Resistance, Infrared sensors

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The thermionic thermal detector (TTD) sense IR radiation by temperature modulation of thermionic emission current within a silicon Schottky diode. The thermionic emission current is the well known Richardson dark current. The TTD operates in the LWIR band. The physics of TTD operation is distinct from that of silicon Schottky barrier MWIR detectors, such as PtSi/Si which are based on internal photoemission. In fact, the TTD has high detection efficiency. The architecture of a TTD array is very similar to that of microbolometer arrays, expect the detector elements are thermally isolated Schottky diodes, operating under reverse bias. When the TTD array is illuminated by an IR image, the temperature of individual detector elements will vary with the local incident power of the image. Under small signal conditions, the dark current of individual detectors will vary as temperature, resulting in an electronic image of the IR scene. The reverse bias dark current of a Schottky diode varies exponentially with temperature. For the small temperature variations observed on the focal pane of an uncooled sensor, this variation is approximately linear. The rate of temperature variation is determined by the Schottky barrier potential and, to a lesser extent by the applied bias potential. The operating temperature range of the detector can be designed into the device by selecting a metal with the appropriate Schottky barrier height. Experimental Schottky barrier heights were determined using Richardson dark current activation energy analysis. Devices optimized for operating at room ambient temperature have a 6 percent K temperature coefficient. The use of Schottky diode thermionic emission for uncooled IR imaging offers several advantages relative to current technology. TTD manufacture is 100 percent silicon processing compatible. Schottky barrier based thermionic emissions array have the same uniformity characteristics as MWIR Schottky barrier photoemissive arrays. Operating TTDs in reverse bias provides a high impedance 'current source' to the multiplexer, resulting in negligible Johnson noise. This mode of operation also results in negligible detector 1/f-noise and drift. In addition, the TTD thermionic emission detection process has high efficiency, fully comparable with the best current thermal detectors.

Proceedings Article | 8 September 1995 Paper

Improved cell design for Schottky barrier infrared detector arrays

Freeman Shepherd, Jonathan Mooney, Alexis Tzannes, James Murguia

Proceedings Volume 2552, (1995) https://doi.org/10.1117/12.218235

KEYWORDS: Sensors, Electrodes, Detector arrays, Diodes, Infrared detectors, Doping, Infrared radiation, Multiplexers, Active sensors, Charge-coupled devices

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