RelativeResourceManager(6)

RelativeResourceManager(6) - Time-domain detection and...

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Time-domain detection and optical photodetectors Chem 420 September 15, 2008
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Slit width and spectrometer resolution z Entrance and exit slits—usually the same width z Optimal width based upon grating dispersion z Tradeoff with sensitivity
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Measuring optical spectra in time rather than frequency space
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Advantages of Fourier transform optical measurements z Throughput (Jaquinot) advantage z Reduced number of optical elements (no slits) leads to more transmitted light (greater S/N) z Wavelength accuracy (Connes) advantage z Multiplex (Fellgett) advantage z Entire spectrum taken simultaneously in ~ 1 second or less z Many more spectra can be acquired in a given time frame and thus S/N increases as (n) 1/2 z Advantage in IR, disadvantage in UV-vis
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Michelson interferometer (Skoog Chapter 7-I) z Converts high frequency optical signal (10 12 -10 15 Hz) to observable frequency z Radiation is split into two beam paths of varying pathlength. z Recombination gives interference that is dependent upon difference in pathlength for a given optical frequency. z Pathlength is dynamically changed to give a lower frequency read-out.
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Interferograms
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Gratings vs. Interferometers Frequency vs. Time Domain Measurements z Multiple wavelengths require scanning or array detectors z Typically no real-time wavelength reference z Easier conceptual operation z Multiplex disadvantage in IR advantage in UV z Multiple wavelengths inherent; FFT yields spectrum z Real-time wavelength reference z Higher throughput at constant resolution z Multiplex advantage in IR disadvantage in UV
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Optical Photodetectors A. PMT B. CdS photoconductivity C.
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RelativeResourceManager(6) - Time-domain detection and...

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