hw3part2

hw3part2 - 20.309: Biological Instrumentation and...

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1 20.309: Biological Instrumentation and Measurement Laboratory Fall 2006 Homework Set 3.5 Sensitive optoelectronic detectors: seeing single photons Due by 12:00 noon (in class) on Tuesday, Nov. 7, 2006. This is another hybrid lab/homework; please see Section 3.4 for what you need to turn in. Contents 1 Objectives 1 2 Background 2 2.1 Photomultiplier Tube (PMT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2.2 Noise Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.2.1 Photon Shot Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.2.2 Electron Shot Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.2.3 Johnson Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3 Experimental Procedures 4 3.1 Hardware set-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.2 Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.3 Experiment Roadmap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.4 Data Analysis and “Deliverables” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Objectives 1. Understand the principles of operation of photomultiplier tubes (PMTs). 2. Build signal conditioning electronics to capture and detect the optical signal generated by a photomultiplier tube. 3. Observe single-photon events with the detector. 4. Understand some of the noise characteristics of the PMT-circuit system as affected by light level and gain. 1
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20.309: Biological Instrumentation and Measurement Laboratory Fall 2006 2 Background 2.1 Photomultiplier Tube (PMT) For low light-level detection and measurement, you can’t beat the photomultiplier. This clever device allows a photon to eject an electron from a light-sensitive alkali metal photocath- ode. The photomultiplier then amplifies this feeble photocurrent by using a high voltage to accelerate the electron onto successive surfaces (dynodes), from which a cascade of additional electrons is easily generated (Figure 1). This use of “electron multiplication” yields extremely low-noise amplification of the initial photocurrent signal. The final current is col- lected by the anode, usually run near ground potential. Figure 1: Principle of PMT operation: a high neg- ative voltage applied to the photocathode acceler- A PMT is a linear device in the sense that the current output is proportional to the ates electrons down the dynode chain. light
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hw3part2 - 20.309: Biological Instrumentation and...

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