Fig. 1. Double-comb surface shape measuring system. (a) Experimental setup; (b) output spectrum of electro-optical comb

Fig. 2. Time domain characteristics of dual-comb. (a) Time domain dual-comb interferometric sequence; (b) partial enlargement

Fig. 3. Single-cycle dual-comb interferogram

Fig. 4. Test of system stability. (a) Allen deviation; (b) deviation

Fig. 5. Dual-comb measurement result under galvanometer scanning

Fig. 6. Measured signal and reference signal reflected by surface of sample 1

Fig. 7. Surface morphologies of sample 1. (a) 3D topography of antenna sample 1 with physical picture shown in inset; (b) result of surface fitting

Fig. 8. Surface morphologies of sample 2. (a) 3D topography of antenna sample 2 with physical picture shown in inset; (b) result of surface fitting