Figure 2
Through-focus series of an asymmetric double slit, whose rectangle openings are of 0.12 μm width for the left slit and 0.035 μm width for the right slit, with a 0.8 μm spacing between the slits d s : (a) in-focus condition (Δf = 0 mm), (b) Fresnel condition #1 for defocusing Δf = 4 mm estimated from the lens current, (c) Fresnel condition #2 for defocusing Δf = 7 mm and interference-fringe spacing s = 8 nm, and (d) pre-Fraunhofer condition for Δf = 16 mm and s = 15 nm. In Fig. 2(d), the images of each single slit show Fraunhofer patterns but they do not overlap; therefore, the image of the double slit is under the Fresnel condition. However, two-wave interference fringes between the Fraunhofer patterns are observed as in Fig. 3(b-2).
