ECEG287 Optical Detection Course Notes Part 1: Introduction

1. ECEG287 Optical Detection Course NotesPart 1: Introduction Profs. Charles A. DiMarzio and Stephen W. McKnight Northeastern University, Spring 2004 DiMarzio & McKnight, Northeastern University

2. Electromagetic Radiation: Classical and Quantum Stephen McKnight DiMarzio & McKnight, Northeastern University

3. Classical Maxwellian EM Waves v=c λ E H H x E E z H λ=c/υ y c=3x108 m/s (free space) υ = frequency (Hz) DiMarzio & McKnight, Northeastern University

4. VIS= 0.40-0.75μ γ-Ray RF Electromagnetic Spectrum (by λ) UV= Near-UV: 0.3-.4 μ Vacuum-UV: 100-300 nm Extreme-UV: 1-100 nm IR= Near: 0.75-2.5μ Mid: 2.5-30μ Far: 30-1000μ 10 nm =100Å 0.1 μ 1 μ 10 μ 100 μ = 0.1mm (300 THz) 0.1 Å 1 Å 10 Å 1 mm 1 cm 0.1 m X-Ray Soft X-Ray Mm-waves Microwaves DiMarzio & McKnight, Northeastern University

5. Quantum Optics: Photoelectric Effect UV Light (λ, Intensity) window i anode In2 > In1 i In1 Emitted Photo-electrons + – V V Vm DiMarzio & McKnight, Northeastern University

6. Photoelectric Effect (1/λ)min depends on metal type, surface condition, adsorbed gasses, but not on light intensity. Vm 1/λ (1/λ)min DiMarzio & McKnight, Northeastern University

7. Photoelectric Effect Explained:Einstein (1905) Energy metal vacuum wave-packet or photon Tmax Eυ=hυ vacuum level w Fermi Energy, Ef h(c/λ) = hυ = w + Tmax w=metal work function h=Planck’s constant =4.14x10-14 eV-s Tmax=electron maximum kinetic energy = qVm surface DiMarzio & McKnight, Northeastern University

8. Quantum Optics: Photoelectric Effect UV Light (λ, Intensity) window i In2 > In1 i In1 Emitted Photo-electrons (½mv2=Tm= hν-w) + – V V Vm=Tm/q DiMarzio & McKnight, Northeastern University

9. Photoelectric Effect (hυ)min is the work function. Depends on metal type, surface condition, adsorbed gasses, but not on light intensity. Vm hυ (hυ)min= w DiMarzio & McKnight, Northeastern University

10. VIS= 3.1-1.66 eV γ-Ray RF Electromagnetic Spectrum (by hυ) UV= Near-UV: 3.1-4.1 eV Vacuum-UV: 4.1-12.4 eV Extreme-UV: 12.4- 1240 eV IR= Near: 0.5-1.66 eV Mid: 41-500 meV Far: 1.4-41 meV 10 nm =100Å 0.1 μ =12.4 eV 1 μ =1.24 eV 10 μ = .124 eV 100 μ = 0.1mm 0.1 Å 1 Å 10 Å 1 mm 1 cm 0.1 m (120 keV) (12 keV) (1.2 keV) (1.24 meV) (124 μeV) (12 μeV) X-Ray Soft X-Ray Mm-waves Microwaves DiMarzio & McKnight, Northeastern University

11. Introduction to Optical Detectionand Course Overview Chuck DiMarzio DiMarzio & McKnight, Northeastern University

12. 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. DiMarzio & McKnight, Northeastern University

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

14. 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 DiMarzio & McKnight, Northeastern University

15. Some Notation DiMarzio & McKnight, Northeastern University

16. 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 General Detector Issues DiMarzio & McKnight, Northeastern University

17. Square-Law Detector DiMarzio & McKnight, Northeastern University

18. Noise Signal + Noise Ps Ps Pn DiMarzio & McKnight, Northeastern University

19. Thermal Detectors Photon Detectors Two Basic Detection Concepts i/P Absorber hn e- Heat Sink l Photon Energy: E=hn=hc/l Total Energy: Pt Photon Count: np=Pt/hn Electron Count: ne=hqPt/hn Electron Rate: ne/t=hqP/hn Current: ene/t=(hqe/hn)P Power: P Heating: (dT/dt)H = CP Cooling: k(dT/dt)C =(T-Ts) Steady State: (T-Ts)/kC = P DiMarzio & McKnight, Northeastern University

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

21. Envelope Transmission Cathode Quantum Efficiency Cutoff Wavelength Gain and High Voltage Dark Current Frequency Response Dead Time Magnetic Fields Damage Thresholds Anode Current Optical Power Photomultiplier Issues DiMarzio & McKnight, Northeastern University

22. Bandgap Energy Window Transmission? Quantum Efficiency Gain Frequency Response / Size Etendue Bias Considerations Cooling Damage Thresholds Optical Power Photocurrent NEP, D* Semiconductor Detector Issues DiMarzio & McKnight, Northeastern University

23. Thermal Detector Issues • Sensitivity • Damage Threshold Power • Frequency Response • Calibration • Repeatability • Spatial Uniformity • Spectral Uniformity • Acceptance Angle DiMarzio & McKnight, Northeastern University