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EE119 Discussion Section 7

# EE119 Discussion Section 7 - (300K what is the minimum...

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EE119 Discussion Section 7 (03/15/10) Professor: Jeff Bokor TA: Xi Luo I. Photomultiplier Tube Example: A PMT with 8 dynodes and 5 = δ is used to detect a laser beam at nm 630 = λ . The quantum efficiency of the PMT at this wavelength is ~50%. Assume the laser power incident on the PMT is 3 × 10 -9 W. - Photoelectric effect What is the maximum possible value of the work function of the photocathode? - Quantum efficiency How many photo-electrons are generated at the photocathode per second? - Gain What is the anode current? - Dark current a) If the cathode dark current is found to be 5x10 4 e/sec at room temperature
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Unformatted text preview: (300K), what is the minimum detectable power of this PMT? b) What would the cathode dark current be if you cool the PMT down to 200K? Does it suggest a way of reducing the dark current? What is the minimum detectable power now? How much improvement in the sensitivity of the PMT you’ve gained in cooling it down? - Shot noise; Poisson statistics; SNR Given the same cathode dark current at 300K, what is the shot noise? What is the signal-to-noise ratio? Assume the bandwidth is 1Hz, which means that, the integration time is 1 sec. II. Brief intro to semiconductor and p-n junction...
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