Figure 2.
(a) The expected time domain signal from an 80 MHz lasing system as observed by the detector: t1 is the pulse width of the ultrafast pulses, t2 is the time between pulses, and t3 is the period of the sinusoidal modulation. (b) Separation of the time domain signal into its time domain components. (c) The Fourier transform of each of the time domain components into their frequency domain counterparts. (d) Recombining the frequency domain counterparts gives the overall frequency domain content as observed by the detector. LIA with a sinusoidal reference tuned to the modulation frequency is only able to recover the signal's fundamental frequency contribution, f3, and misses the contributions from the higher frequency doublets.