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Detection Methods. Coherent ↔ Incoherent Photon Detection ↔ Bolometric Photon Counting ↔ Integrating. Radio Telescopes. Typical Designs Heterodyne Receivers. Jansky’s First Radio Telescope 1933. Grote Reber: 1937 Radio Telescope. The Arecibo Radio Telescope. Heterodyne Receivers.
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Detection Methods • Coherent ↔ Incoherent • Photon Detection ↔ Bolometric • Photon Counting ↔ Integrating
Radio Telescopes • Typical Designs • Heterodyne Receivers
Heterodyne Receivers • Mix signal and local oscillator • Mixed signal contains “intermediate frequency” f_signal – f_local but also the sum of the frequencies
MM and Sub-MM Telescopes • Use both coherent and incoherent detection • Heterodyne receivers for emission-lines • Mostly bolometers for continuum
Bolometers • Absorb and thermalize photons • Measure temperature change • Balance between heating and cooling results in long time constants • Typically used in chopped operation
Transition Edge Sensors: Extreme sensitivity to small temperature changes allows to build very sensitive bolometer arrays
Photocathods • The photoelectric effect • Quantum nature of light • Photomultipliers, channel plates …
Photocathod Devices • Cathods • Photomultiplier • Image intensifiers • Microchannel plates
Physics of Semiconductors Basic Quantum Physics Solids Semiconductors PN Junctions