Fig. 7.

Schematic of high-order photobleaching and ablation of Hoechst molecules. Violet arrows correspond to wavelengths from 720 up to 920 nm, yellow arrows to 920 nm and above. In photobleaching two or three photons evoke the excitation of Hoechst and another two photons are sequentially absorbed in saturated one photon transitions, while in ablation multiphoton-ionization occurs by the quasi-simultaneous absorption of four or five photons.