(a,c) Show respectively an example of the radial (a) and axial (c) intensity distribution of a 100 nm fluorescent bead excited with single photon excitation at 405 nm collected with a 10X, 0.3 NA. (b,d) Show respectively an example of the radial (b) and axial (d) intensity distribution of a 100 nm fluorescent bead excited with two-photon excitation at 740 nm collected with the same objective as in single photon case. (e) shows the linear profile of the intensity distribution shown in (a,b). The Full Width at Half Maximum (FWHM) of these profiles gives a direct estimate of the radial Point Spread Function of the system in 1P and 2P regimes (data shown in Table 1). Similarly (f) shows the axial profiles of the intensity distribution for single and two-photon excitation. Scale bars are 4 μm for (a,b) 1 μm (along z) for (c,d).