Figure 4

Transmission ratios at 400 nm and 800 nm, T ₄₀₀/T ₈₀₀, at different times after single pulse of E _p  = 200 nJ focused by \(NA\equiv n\,{\rm{s}}{\rm{i}}{\rm{n}}\,\alpha =1.25\) (α = 55.6°) objective lens (shown by a triangle); the optical resolution of the FFT filter was 0.89 μm marked by ellipse. Fringing is caused by division of two images with similar intensity values and the FFT enhanced  oscillations.