Jan 2004 Chuck DiMarzio, Northeastern University b-1 ECEG287 Optical Detection Course Notes Part 3: Noise and Photon Detection Profs. Charles A. DiMarzio and Stephen W. McKnight Northeastern University, Spring 2004

Jan 2004 Chuck DiMarzio, Northeastern University b-2 Topic Outline Noise Sources –Overview of Noise Sources –A Simple Noise Model Photon Noise - Fundamental Limit Photon Detectors –Quantum Efficiency –Gain –Types and Examples Other Noise Sources

Jan 2004 Chuck DiMarzio, Northeastern University b tex:1 Noise Sources Photon Noise - Fundamental Limit Johnson Noise G-R Noise Background Noise Electronic Noise

Jan 2004 Chuck DiMarzio, Northeastern University b-4 Classical Noise Model Add Field Amplitudes Re U Im U UsUs UnUn tex:2

Jan 2004 Chuck DiMarzio, Northeastern University b-5 Photon Noise tex: tex:5 nn nn RMS eiei eiei nn 

Jan 2004 Chuck DiMarzio, Northeastern University b-6 Photon Detector Concepts Quantum Efficiency (spectral dependence) Gain Responsivity –Current or Voltage Noise –Current or Voltage Mechanisms of Detection –Later, for Specific Devices

Jan 2004 Chuck DiMarzio, Northeastern University b-7 Photon Detector Responsivity 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: i = en e /t=(  q e/h )P w    q e/h hWhW

Jan 2004 Chuck DiMarzio, Northeastern University b-8 Photon Detector Gain tex:6 qq G Signal Noise

Jan 2004 Chuck DiMarzio, Northeastern University b-9 Photon Counting (1) 05 Clock Gate Counter t Clock Signal t Photon Arrival t Photon Count 312 Probability Density n Experimental Setup to measure the probability distribution of photon number.

Jan 2004 Chuck DiMarzio, Northeastern University b-10 Photon Counting (2) t Photon Arrival t Anode Electrons t and Threshold Photon counting threshold removes gain fluctuations but misses multiple counts. It does not reduce dark counts. t Photocathode Electrons Error 1: Dark Count: Counted an electron when no photon was present. Error 2: Missed Count: Counted one electron when two photons were present. t Photocathode Electron Count t True Count

Jan 2004 Chuck DiMarzio, Northeastern University b-11 Photon Detector Types Photoemissive –Vacuum Photodiodes –Photomultipliers –Low Quantum Efficiency, High Gain Semiconductor –Photoconductive Intrinsic and Extrinsic High Quantum Efficiency High Gain Example: Avalanche Photodiode –Photovoltaic Intrinsic and Extrinsic High Quantum Efficiency No Gain Low Noise

Jan 2004 Chuck DiMarzio, Northeastern University b-12 Photon Detector Characteristics Advantages –Sensitivity –Low Noise –Speed –Small Size Disadvantages –Difficult Calibration –Damage Susceptibility Other –Ruggedness (?) –Narrow Spectral Range –Cooling Requirement (?)

Jan 2004 Chuck DiMarzio, Northeastern University b-13 Other Noise Sources Johnson Noise G-R Noise Background Noise Electronic Noise

Jan 2004 Chuck DiMarzio, Northeastern University b-14 Thermal Noise tex: tex:8 Stopped here Wed 14 Jan 04

Jan 2004 Chuck DiMarzio, Northeastern University b-15 NEP Example tex: tex:10

Jan 2004 Chuck DiMarzio, Northeastern University b-16 Detectivity, D* tex: tex:12

Jan 2004 Chuck DiMarzio, Northeastern University b-17 Background Noise tex: tex:14 Signal Bkg

Jan 2004 Chuck DiMarzio, Northeastern University b-18 Some Simplified Backgrounds tex: tex:15

Jan 2004 Chuck DiMarzio, Northeastern University b-19 Background Noise tex:17 Signal Bkg with Fluctuations

Jan 2004 Chuck DiMarzio, Northeastern University b-20 Background NEP tex: tex:19

Jan 2004 Chuck DiMarzio, Northeastern University b-21 Detectivity Limits and Example tex: tex:21

Jan 2004 Chuck DiMarzio, Northeastern University b-22 Detector Examples: Spectral Photon Radiance

Jan 2004 Chuck DiMarzio, Northeastern University b-23 Detector Examples: Detectivity, D*

Jan 2004 Chuck DiMarzio, Northeastern University b-24 Detector Examples: Total Background Power

Jan 2004 Chuck DiMarzio, Northeastern University b-25 Detector Examples: NEP