6 Application Note
DC3100 35
6.1.2
Frequency Domain FLIM
The lifetime can also be determined in the frequency domain by using a modulated
light source. The source continuously emits a sine wave signal in the range of 1 to
200MHz and modulates the fluorescence. Due to the lifetime of the electrons in the
excited state there will be a phase shift between the excitation signal and the
fluorescence response. Furthermore, the intensity to the excitation and fluorescence
sine waves will be modulated. The lifetime can be calculated from the modulation
ratio of the intensity. Hence, the FLIM in the frequency domain provides 2 values for
the lifetime.
Figure 36 Frequency Domain FLIM