(a) The lateral plane and (b) the vertical plane. We deem that the influence of coma effect caused by the ×100/1.4 objective lens is insignificant since this type of objective is aplanatic which dispels coma influence of the objective. Also, the focal spot has a well-defined symmetric shape before patterning the photoresist as is displayed in Figure  1b. In addition, the extents of coma effect, which is shown in Figure  3a, b, c, are different under the same experimental conditions. Therefore, we consider that coma effect of the laser lithography system should be caused by mechanical #selleckchem randurls[1|1|,|CHEM1|]# disturbance. In fact, the mechanical vibration during the system working may disturb the laser beam

and then induce an angle of deviation between the laser beam and objective lens. Astigmatism influence Figure  6a presents images of the other kind of nanopillar with distorted pattern caused by astigmatism besides the situations shown in Figure  3 (the noise of background in Figure  6a is due to AFM software processing). We take the typical pattern marked by Dactolisib supplier the arrow in Figure  6a. Figure  6b, c presents the zoomed-in images

of the marked nanopillar in Figure  6a. In Figure  6b, c, dark lines pass through the top of the nanopillar, and they are drawn as the symmetry axes for the nanostructure in two perpendicular directions. Figure  6d, e presents the cross sections along the dark lines in Figure  6b, c, respectively. In Figure  6, it is obvious that the nanostructures fabricated by laser lithography are almost located at the center of the patterns; however, they are an elliptic cylinder. It is also evident that the patterns in Figure  6b, c,d,e are symmetric to the two dark lines, but not completely the same as that in Figure  5a. As has been explained earlier, spherical aberration influence is negligible since an aplanatic lens is employed as the objective lens. Therefore,

this kind of experimental phenomenon could only be induced by astigmatism effect. Figure 6 Images of the other kind Anidulafungin (LY303366) of nanopillar. (a) AFM image of the other kind of nanopillar. (b, c) Enlarged image of the marked pattern in (a) along different directions. (d, e) The corresponding cross sections of (b) and (c). Figure  7 is the numerical simulation of astigmatism influence on the donut-shaped focal spot. Figure  7a,b,c,d shows the intensity distribution calculated with different A a values which are 0.05, 0.1, 0.2, and 0.3, respectively. The corresponding profiles of intensity distribution along x = y and x = −y are shown in Figure  7e, f, g, h. In Figure  7a, b, c,d, some clues about the gradual transformation of the donut-shaped laser spot could be found. As A a is increasing, the laser pattern is pulled into two opposite directions and finally separated into two parts while the center shape varies from a circular to a belt-like structure.