lect21 - Thermal and Photon Detectors – Introduction to...

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Unformatted text preview: Thermal and Photon Detectors – Introduction to Photodetectors – Quantum Efficiency – Photon Detectors – Thermal Detectors – Noise Considerations Photodetectors • Optical detection – Process that converts optical signal to electrical signal • Photodetector – Too slow to follow instantaneous signal – Square Law device: output proportional to optical power • Sensitivity – Needs to be sensitive to particular wavelength of light • Speed – Needs to have a fast enough response to follow modulation of the optical signal • Responsivity: electrical current to optical power Photodetectors: “Figures of Merit” quantum efficiency Photodetectors: “Figures of Merit” • Noise Equivalent Power (NEP) – Minimum optical power required to maintain a signal- to-noise ratio of 1 • Normalized detectivity (D*) – “A” is the detector area – Gives measure of intrinsic quality of detector material NEP A D * Photodetectors: “Figures of Merit” • Quantum Efficiency ( ) – The ratio of countable events produced by photons incident on detector to the number of photons photons incident of number emitted electrons of number ) ( Types of Detectors • Photon detectors – Photons interact with detector material and generate free electrons – Types of Photon Detectors: • Photoemissive- Incident photons release electrons from surface of material • Photoconductive (semiconductor) - Electrical conductivity of material changes with intensity of incident light ( often reverse biased) • Photovoltaic (semiconductor) - Voltage is generated from optical energy (zero bias - photocurrent is restricted, voltage builds up) • Thermal detectors – Convert photon energy into heat Photoelectron Emission Book: 18.1 Photoelectric work function • Response vs. Wavelength – Photon detectors: photon must have enough energy to free an electron Types of Detectors hc E Photoemissive Detectors...
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This note was uploaded on 02/12/2012 for the course ECE 414 taught by Professor Alenxendra during the Spring '11 term at Purdue.

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lect21 - Thermal and Photon Detectors – Introduction to...

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