April 2004 DiMarzio & McKnight, Northeastern University ECEG287 Optical Detection Course Notes Part 19: Conclusion Profs. Charles A. DiMarzio and Stephen W. McKnight Northeastern University, Spring 2004

April 2004 DiMarzio & McKnight, Northeastern University Electromagnetic Spectrum (by λ) 1 μ10 μ100 μ = 0.1mm 0.1 μ10 nm =100Å VIS= μ 1 mm1 cm0.1 m IR= Near: μ Mid: μ Far: μ UV= Near-UV: μ Vacuum-UV: nm Extreme-UV: nm MicrowavesX-RayMm-waves 10 Å1 Å0.1 Å Soft X-RayRFγ-Ray (300 THz)

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

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

April 2004 DiMarzio & McKnight, Northeastern University Square-Law Detector

April 2004 DiMarzio & McKnight, Northeastern University Noise Signal + Noise PsPs PsPs PnPn

April 2004 DiMarzio & McKnight, Northeastern University 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: NE  T

April 2004 DiMarzio & McKnight, Northeastern University Two Basic Detection Concepts Thermal DetectorsPhoton Detectors e-e- h Photon Energy: E=h =hc/ Total Energy: Pt Photon Count: n p =Pt/h Electron Count: n e =  q Pt/h Electron Rate: n e /t=  q P/h Current: en e /t=(  q e/h )P Absorber Heat Sink Power: P Heating: (dT/dt) H = CP Cooling:  (dT/dt) C =(T-T s ) Steady State: (T-T s )/  C = P i/P Stopped Mon 5 Jan 04

April 2004 DiMarzio & McKnight, Northeastern University Detector Types Thermal –Characteristics Wide Bandwidth Accuracy –Examples Thermocouple Thermopile Pyroelectric Photon –Characteristics Speed Sensitivity –Examples Photoemissive Photoconductive - intrinsic & extrinsic Photovoltaic - intrinsic & extrinsic

April 2004 DiMarzio & McKnight, Northeastern University 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 DiMarzio & McKnight, Northeastern University 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 Array Detectors 18 - Odds and Ends

April 2004 DiMarzio & McKnight, Northeastern University SNR Layout for Coherent Detection PsPs P BKG BPF Preamp Amp P LO Filter?