Incoherent Photon Detection Bolometric Photon Counting Integrating Radio Telescopes Typical Designs Heterodyne Receivers Janskys First Radio Telescope 1933 Grote Reber 1937 Radio Telescope ID: 673765
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Slide1Slide2
Detection Methods
Coherent ↔ IncoherentPhoton Detection
↔
Bolometric
Photon Counting
↔ IntegratingSlide3
Radio Telescopes
Typical DesignsHeterodyne ReceiversSlide4
Jansky’s First Radio Telescope
1933Slide5
Grote Reber: 1937 Radio TelescopeSlide6Slide7Slide8Slide9Slide10
Heterodyne Receivers
Mix signal and local oscillatorMixed signal contains “intermediate frequency”
f_signal – f_local
but also the sum of the frequenciesSlide11
Heterodyne Signal DetectionSlide12Slide13Slide14Slide15
MM and Sub-MM Telescopes
Use both coherent and incoherent detectionHeterodyne receivers for emission-linesMostly bolometers for continuumSlide16
Millimeter Valley on Mauna KeaSlide17Slide18
NGC 6334Slide19Slide20
Detection Methods
Coherent ↔ IncoherentPhoton Detection
↔
Bolometric
Photon Counting
↔ IntegratingSlide21
Bolometers
Absorb and thermalize photonsMeasure temperature changeBalance between heating and cooling results in long time constantsTypically used in chopped operationSlide22Slide23Slide24Slide25Slide26Slide27Slide28
Transition Edge Sensors: Extreme sensitivity to small temperature changes allows to build very sensitive bolometer arraysSlide29Slide30
Photocathods
The photoelectric effectQuantum nature of lightPhotomultipliers, channel plates …Slide31
Detection Methods
Coherent ↔ IncoherentPhoton Detection
↔
Bolometric
Photon Counting
↔ IntegratingSlide32Slide33Slide34Slide35Slide36Slide37Slide38
Photocathod Devices
CathodsPhotomultiplierImage intensifiersMicrochannel platesSlide39
In 1907 Joel Stebbins pioneered the use of photoelectric devices in AstronomySlide40
Photomultiplier tubes: pile up errors
Each detected photon produces a pulse of finite duration, t
0
, which causes a dead time in the detector. The number of pulses (exposure time) is reduced by the amount of overlapping deadtimes.
N = n/(1
–t
0
n)
N is the true rate, and n the apparent rate
Pile-up errors
System blocks completely at high light levelsSlide41Slide42
1840 J.W. Draper makes a photograph of the moon. Followed by photographs of the Sun by Foucault and Fizeau
Sunspots photographed in 1858 by W. De La Rue
Jansen and Lockyer in the 1870s photographed the solar spectrum and discovered the spectral lines of Helium.
Ainsee Common photographed Orion Nebula and these revealed stars and details you could not see in a telescope
Photographs by Hubble in the early 1900‘s established that some nebula where „island universes“ (i.e. galaxies). His spectral observations of galaxies (exposures of more than one night) led to the discovery of the expansion of the Universe.
For 100 years photographic plates/film dominated the field of astronomical detectors.
A Revolution in Detectors: Photographic PlatesSlide43
Detection Methods
Coherent ↔ IncoherentPhoton Detection
↔
Bolometric
Photon Counting
↔ IntegratingSlide44
Physics of Semiconductors
Basic Quantum PhysicsSolidsSemiconductors
PN JunctionsSlide45Slide46Slide47Slide48Slide49Slide50Slide51Slide52
Semiconductors
Conduction in semiconductorsDopingSlide53
Detection Methods
Coherent ↔ IncoherentPhoton Detection
↔
Bolometric
Photon Counting
↔ IntegratingSlide54Slide55Slide56Slide57Slide58Slide59Slide60Slide61Slide62
PN Junctions
Formation of pn junctionRectifying propertiesCharge separating propertiesSlide63Slide64Slide65Slide66Slide67Slide68Slide69Slide70Slide71
Electronics
PN junctions and photodiodesField Effect transistorsLogic devicesAnalog switches
Operational amplifiers
A practical exampleSlide72
Field Effect Transistor
Junction FET (JFET)Metal-Oxide-Semiconductor FET (MOSFET)CMOS circuits (Complementary Oxide Semiconductor)Slide73Slide74Slide75Slide76Slide77Slide78Slide79Slide80Slide81Slide82
Fabrication of Integrated Circuits
DopingDepositing metalGrowing oxides (as isolators)All controlled by photoresist maskingSlide83
HAWAII-2: Photolithographically Abut 4 CMOS Reticles to Produce Each 2048
2
ROIC
Twelve 2048
2
ROICs per 8” Wafer
2048
2
Readout Provides Low Read Noise for Visible and MWIRSlide84
3-D Barrier to Prevent Glow from Reaching the DetectorSlide85Slide86Slide87Slide88Slide89