Abstract
We describe the design and performance of a 10 GHz harmonic-content frequency-domain fluorometer. The modulated excitation is provided by the harmonic content of a train of ps pulses. High speed and/or high frequency detection was attained with a triode-type MCP PMT from Hamamatsu, R-2566-6, with 6 micron channels. To minimize the cost of the electronic components, and to minimize the noise due to these components, the detection circuits consist of two ranges, 10 MHz to 2 CHz and 2-10 GHz. The upper frequency limit of 10 GHz is determined by the current MCP PMT, so the usual configuration includes a low noise 2-10 GHz amplifier. This amplifier is easily replaced with a 2-18 GHz amplifier which allows operation to 18 GHz and the use of faster PMTs, should they become available in the future. Measurement of known optical delays demonstrates the accuracy of the instrument. For instance, a 1.69 ps optical delay was measured as 1.7 0.4 ps from 0.5 - 10 GHz, and 1.7 0.2 ps from 2- 8 GHz, where the uncertainty indicates the maximum deviation from the expected value. The data were shown to be free of systematic errors by measurements on fluorophores with single exponential decays.
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