ECEG 287 Optical Detection Course Notes Part 19

ECEG 287 Optical Detection Course Notes Part 19: Conclusion Profs. Charles A. Di. Marzio and Stephen W. Mc. Knight Northeastern University, Spring 2004 April 2004 Di. Marzio & Mc. Knight, Northeastern University 1

Electromagnetic Spectrum (by λ) UV= Near-UV: 0. 3 -. 4 μ Vacuum-UV: 100 -300 nm VIS= IR= 0. 40 -0. 75μ Near: 0. 75 -2. 5μ Mid: 2. 5 -30μ Extreme-UV: 1 -100 nm 10 nm =100Å 0. 1 Å γ-Ray April 2004 0. 1 μ Far: 30 -1000μ 1μ (300 THz) 1Å 10 Å X-Ray Soft X-Ray 1 mm Mm-waves Di. Marzio & Mc. Knight, Northeastern University 10 μ 100 μ = 0. 1 mm 1 cm 0. 1 m Microwaves RF 2

What is Optical Detection? • The goal is to get information from light. – Usually we look for variations in the amount of light over • • space. . . or time. . . or spectrum. . . or some combination of these. • Generally the output is an electrical signal. – It may be digitized for use in a computer. – We need to measure this signal in the presence of noise. April 2004 Di. Marzio & Mc. Knight, Northeastern University 3

Course Overview 2. Sources and Radiometry 3. Noise 2 -5. Detectors 7. Coherent Detection 8. Signal Statistics 9. Array Detectors April 2004 Di. Marzio & Mc. Knight, Northeastern University 6. Circuits 4

Some Detection Issues • Optics – Radiometry, Beam Shaping, and Filters • Detector Physics – Converting Optical Energy to Electrical • Receiver Circuit – Matching to Detector, Proper Biasing • Interpretation of Data – Dealing with Noise and Signal Statistics April 2004 Di. Marzio & Mc. Knight, Northeastern University 5

General Detector Issues • • Spectral Response Modulation Response Responsivity Noise (NEP) Damage Level Sensitive Area Circuit Considerations Device-Specific Issues April 2004 • Filtering – Angle, Position, Wavelength • Packaging – Window Transmission, Position • Power Requirements • Cooling/Vacuum Requirements Di. Marzio & Mc. Knight, Northeastern University 6

Square-Law Detector April 2004 Di. Marzio & Mc. Knight, Northeastern University 7

Noise Ps Signal + Noise Ps Pn April 2004 Di. Marzio & Mc. Knight, Northeastern University 8

Noise Issues • Optical Signal Power (Watts) – Normally Related to Some Desired Quantity (Reflectivity, Temperature, Distance, Magnetic Field, Scattering, Absorption, etc. ) • NEP (Watts per root Hertz) – Can be Related to “NEX” • Example: NEDT April 2004 Di. Marzio & Mc. Knight, Northeastern University 9

Two Basic Detection Concepts • Thermal Detectors Absorber hn Heat Sink Power: P Heating: (d. T/dt)H = CP Cooling: k(d. T/dt)C =(T-Ts) Steady State: (T-Ts)/k. C = P April 2004 • Photon Detectors i/P e- l Photon Energy: E=hn=hc/l Total Energy: Pt Photon Count: np=Pt/hn Electron Count: ne=hq. Pt/hn Electron Rate: ne/t=hq. P/hn Current: ene/t=(hqe/hn)P Di. Marzio & Mc. Knight, Northeastern University 10 Stopped Mon 5 Jan 04

Detector Types • Photon • Thermal – Characteristics • Wide Bandwidth • Accuracy – Examples • Thermocouple • Thermopile • Pyroelectric April 2004 – Characteristics • Speed • Sensitivity – Examples • Photoemissive • Photoconductive intrinsic & extrinsic • Photovoltaic intrinsic & extrinsic Di. Marzio & Mc. Knight, Northeastern University 11

Course Overview (1) • 3 - Noise and Photon Detectors • - Materials Considertations – (4) in Photoemissive Detectors – (5, 6) in Semiconductor Detectors • 7 - Types of Semiconductor Detectors • 8 - P-N Junction Effects & Other Detectors • 9, 10 - Detectors as Circuit Elements April 2004 Di. Marzio & Mc. Knight, Northeastern University 12

Course Overview (2) • 11, 12 - Coherent Detection • 13 - Semiconductor Photoconductive Detectors • 14 - Signals and Noise • 15 - Intro to Arrays & a bit about color • 16 - Gain & BW in Semiconductor Dets. • 17 - Array Detectors • 18 - Odds and Ends April 2004 Di. Marzio & Mc. Knight, Northeastern University 13

SNR Layout for Coherent Detection PLO Filter? Amp Preamp Ps PBKG April 2004 BPF Di. Marzio & Mc. Knight, Northeastern University 14