Fig. 3.

(a)–(f) Examples of different postprocessing techniques on microtubules in a fixed HeLa cell labeled with Alexa 488. The presence of STED-induced background (uncorrelated) negatively impacts the 2PE CW-STED image; the improvement is effective when this background is efficiently removed. The SPLIT technique has the best performance, similar to that obtained with MID. ${\lambda }_{\mathrm{exc}}=760\mathrm{nm}$ and ${\lambda }_{\mathrm{STED}}=577\mathrm{nm}$. Scale bars: $1\mu \mathrm{m}$.