Cover Picture: Ann. Phys. 3'2013

Biological modulation using a femtosecond‐pulsed laser: When a femtosecond‐pulsed laser (yellow beam) is used to irradiate the cytosol of the cell (upper left), it generates free electrons (blue particles) in the focused area. Laser‐induced free electrons subsequently produce reactive oxygen species (ROS, red particles), which are amplified by inter‐mitochondrial networks. Amplified ROS signals can stimulate endoplasmic reticulum to release calcium ions (green particles). Femtosecond‐pulsed laser stimulation can modify blood vessel permeability (lower right). After short‐term laser irradiation, small chemicals (e.g., drugs) and proteins to which the intact blood vessel is impermeable can now flow out while red blood cells stay within the lumen. The cascade mechanism, which consists of low‐density plasma, ROS and calcium, is responsible for femtosecond‐pulsed laser‐induced biological modulation in both excitable and non‐excitable cells. J. Yoon et al., pp. 205‐214 in this issue