Fig. 1. (a) Intensity distribution in cross-section; (b) one-dimensional horizontal intensity distribution

Fig. 2. Schematic of high-quality Bessel beam generated by CDG

Fig. 3. Schematic of SSOCT system (the solid line represents the optical signal and the dotted line represents the electrical signal)

Fig. 4. Flow chart of data processing algorithm

Fig. 5. (a) Axial point spread function; (b) image of 3 μm microbeads; (c)-(e) lateral point spread functions

Fig. 6. Schematic of a microneedle array and its geometrical shape

Fig. 7. (a) Image of microneedle array inserted into the skin; (b) OCT image before inserting the microneedle; (c)-(e) OCT images of microneedle array inserted into the skin for 0, 30, 60 min, respectively; (f) OCT image after removing the microneedle base plate