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. 2011 Jan 3;2011:870879. doi: 10.1155/2011/870879

Figure 4.

Figure 4

Illustration of frequency-domain fluorescence lifetime measurement. The excitation light (red) is modulated in amplitude at a frequency ω, while the fluorescence light (blue) is emitted with the same modulation frequency but with a phase shift in time, ϕ. For a single exponential lifetime, the value of the fluorescence lifetime is related by tanϕ = ωτ.