ECEG287 Optical Detection Course Notes Part 1: Introduction

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


Electromagetic Radiation: Classical and Quantum

Stephen McKnight


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)


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)


Quantum Optics: Photoelectric Effect

UV Light (λ, Intensity)

V

Emitted Photo-electrons

i

–+

i

VVm

In2 > In1

In1

anode

window


Photoelectric Effect

Vm

1/λ(1/λ)min

(1/λ)min depends on metal type, surface condition, adsorbed gasses, but not on light intensity.


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


Quantum Optics: Photoelectric EffectUV Light (λ, Intensity)

V

Emitted Photo-electrons (½mv2=Tm= hν-w)

i

–+

i

VVm=Tm/q

In2 > In1

In1

window


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.


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)


Introduction to Optical Detectionand Course Overview

Chuck DiMarzio


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.


Course Overview

2. Sources andRadiometry

2-5. Detectors

3. Noise

6. Circuits7. Coherent Detection8. Signal Statistics9. Array Detectors


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


Some Notation


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


Square-Law Detector


NoiseSignal+ NoisePs

Ps

Pn


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


Detector Types

• Thermal– Characteristics

• Wide Bandwidth

• Accuracy

– Examples• Thermocouple

• Thermopile

• Pyroelectric

• Photon– Characteristics

• Speed• Sensitivity

– Examples• Photoemissive• Photoconductive -

intrinsic & extrinsic• Photovoltaic -

intrinsic & extrinsic


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


Semiconductor Detector Issues

• Bandgap Energy• Window

Transmission?• Quantum Efficiency• Gain• Frequency Response /

Size• Etendue

• Bias Considerations• Cooling• Damage Thresholds• Optical Power• Photocurrent• NEP, D*


Thermal Detector Issues

• Sensitivity• Damage Threshold Power• Frequency Response• Calibration• Repeatability• Spatial Uniformity• Spectral Uniformity• Acceptance Angle

ECEG287 Optical Detection Course Notes Part 1: Introduction

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