Jan 2004 DiMarzio & McKnight, Northeastern University 10464-1-1
ECEG287 Optical Detection Course Notes
Part 1: Introduction
Profs. Charles A. DiMarzio
and
Stephen W. McKnight
Northeastern University, Spring 2004
Jan 2004 DiMarzio & McKnight, Northeastern University 10464-1-2
Electromagetic Radiation: Classical and Quantum
Stephen McKnight
Jan 2004 DiMarzio & McKnight, Northeastern University 10464-1-3
Classical Maxwellian EM Waves
E E
E
x
y
z H
HH
λ
v=c
λ=c/υ
c=3x108 m/s (free space)
υ = frequency (Hz)
Jan 2004 DiMarzio & McKnight, Northeastern University 10464-1-4
Electromagnetic Spectrum (by λ)
1 μ 10 μ 100 μ = 0.1mm
0.1 μ10 nm =100Å
VIS=
0.40-0.75μ
1 mm 1 cm 0.1 m
IR=
Near: 0.75-2.5μ
Mid: 2.5-30μ
Far: 30-1000μ
UV=
Near-UV: 0.3-.4 μ
Vacuum-UV: 100-300 nm
Extreme-UV: 1-100 nm
MicrowavesX-Ray Mm-waves
10 Å1 Å0.1 Å
Soft X-Ray RFγ-Ray
(300 THz)
Jan 2004 DiMarzio & McKnight, Northeastern University 10464-1-5
Quantum Optics: Photoelectric Effect
UV Light (λ, Intensity)
V
Emitted Photo-electrons
i
–+
i
VVm
In2 > In1
In1
anode
window
Jan 2004 DiMarzio & McKnight, Northeastern University 10464-1-6
Photoelectric Effect
Vm
1/λ(1/λ)min
(1/λ)min depends on metal type, surface condition, adsorbed gasses, but not on light intensity.
Jan 2004 DiMarzio & McKnight, Northeastern University 10464-1-7
Photoelectric Effect Explained:Einstein (1905)Energy
w
Tmax
h(c/λ) = hυ = w + Tmax
Eυ=hυ vacuum level
metal vacuum
surface
Fermi Energy, Ef
wave-packet or photon
w=metal work function
h=Planck’s constant =4.14x10-14 eV-s
Tmax=electron maximum kinetic energy = qVm
Jan 2004 DiMarzio & McKnight, Northeastern University 10464-1-8
Quantum Optics: Photoelectric EffectUV Light (λ, Intensity)
V
Emitted Photo-electrons (½mv2=Tm= hν-w)
i
–+
i
VVm=Tm/q
In2 > In1
In1
window
Jan 2004 DiMarzio & McKnight, Northeastern University 10464-1-9
Photoelectric Effect
Vm
hυ
(hυ)min= w
(hυ)min is the work function. Depends on metal type, surface condition, adsorbed gasses, but not on light intensity.
Jan 2004 DiMarzio & McKnight, Northeastern University 10464-1-10
Electromagnetic Spectrum (by hυ)
1 μ
=1.24 eV
10 μ
= .124 eV
100 μ = 0.1mm
0.1 μ
=12.4 eV
10 nm =100Å
VIS=
3.1-1.66 eV
1 mm 1 cm 0.1 m
IR=
Near: 0.5-1.66 eV
Mid: 41-500 meV
Far: 1.4-41 meV
UV=
Near-UV: 3.1-4.1 eV
Vacuum-UV: 4.1-12.4 eV
Extreme-UV: 12.4- 1240 eV
MicrowavesX-Ray Mm-waves
10 Å1 Å0.1 Å
Soft X-Ray RFγ-Ray(1.2 keV)(12 keV)(120 keV) (124 μeV)(1.24 meV) (12 μeV)
Jan 2004 DiMarzio & McKnight, Northeastern University 10464-1-11
Introduction to Optical Detectionand Course Overview
Chuck DiMarzio
Jan 2004 DiMarzio & McKnight, Northeastern University 10464-1-12
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.
Jan 2004 DiMarzio & McKnight, Northeastern University 10464-1-13
Course Overview
2. Sources andRadiometry
2-5. Detectors
3. Noise
6. Circuits7. Coherent Detection8. Signal Statistics9. Array Detectors
Jan 2004 DiMarzio & McKnight, Northeastern University 10464-1-14
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
Jan 2004 DiMarzio & McKnight, Northeastern University 10464-1-15
Some Notation
Jan 2004 DiMarzio & McKnight, Northeastern University 10464-1-16
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
Jan 2004 DiMarzio & McKnight, Northeastern University 10464-1-17
Square-Law Detector
Jan 2004 DiMarzio & McKnight, Northeastern University 10464-1-18
NoiseSignal+ NoisePs
Ps
Pn
Jan 2004 DiMarzio & McKnight, Northeastern University 10464-1-19
Two Basic Detection Concepts
• Thermal Detectors • Photon Detectors
e-
h
Photon Energy: E=h=hc/Total Energy: PtPhoton Count: np=Pt/hElectron Count: ne=qPt/hElectron Rate: ne/t=qP/hCurrent: ene/t=(qe/h)P
Absorber
HeatSink
Power: PHeating: (dT/dt)H = CPCooling: (dT/dt)C =(T-Ts)Steady State: (T-Ts)/C = P
i/P
Jan 2004 DiMarzio & McKnight, Northeastern University 10464-1-20
Detector Types
• Thermal– Characteristics
• Wide Bandwidth
• Accuracy
– Examples• Thermocouple
• Thermopile
• Pyroelectric
• Photon– Characteristics
• Speed• Sensitivity
– Examples• Photoemissive• Photoconductive -
intrinsic & extrinsic• Photovoltaic -
intrinsic & extrinsic
Jan 2004 DiMarzio & McKnight, Northeastern University 10464-1-21
Photomultiplier Issues
• 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
Jan 2004 DiMarzio & McKnight, Northeastern University 10464-1-22
Semiconductor Detector Issues
• Bandgap Energy• Window
Transmission?• Quantum Efficiency• Gain• Frequency Response /
Size• Etendue
• Bias Considerations• Cooling• Damage Thresholds• Optical Power• Photocurrent• NEP, D*
Jan 2004 DiMarzio & McKnight, Northeastern University 10464-1-23
Thermal Detector Issues
• Sensitivity• Damage Threshold Power• Frequency Response• Calibration• Repeatability• Spatial Uniformity• Spectral Uniformity• Acceptance Angle