Figure 3
From: Direct frequency comb optical frequency standard based on two-photon transitions of thermal atoms
High quality TPTs spectrum of 87Rb with eliminated Doppler broadening background.
(a) The observed spectrum of 87Rb Doppler-free TPTs directly excited by the frequency comb with the frep scanned around 144.198 MHz. (b) The 5S1/2 (F = 2) to 5D5/2(F = 4) TPT transition. This TPT has the highest SNR among all of the transitions and is selected for the stabilization of the frequency comb.
