Numerical simulation of astigmatism influence on the donut-shaped focal spot. Simulated light intensity distribution vs astigmatism coefficient. (a) Aa = 0.05, (b) Aa = 0.1, (c) Aa = 0.2, and (d) Aa = 0.3. Intensity along x = y and x = −y (e) Aa = 0.05, (f) Aa = 0.1, (g) Aa = 0.2, and (h) Aa = 0.3.
Zhang et al. Nanoscale Research Letters 2013 8:280 doi:10.1186/1556-276X-8-280