Device for light based skin treatment

A method for optical coupling of an incident light beam from a device for light based skin treatment into a skin, the method comprising:

• applying a fluid to the skin to be treated,
• pressing a substitutable multi-layered integrated interface element onto the portion of the skin covered with the applied fluid,
• the multi-layered integrated interface element comprising:
• a first layer, closest to the skin, consisting of a transparent foil,
• a second fluid layer comprising a transparent mixture of a polar and an apolar substance,
• a third layer comprising a transparent exit window, such that the transparent mixture is applied directly to an outer surface of the transparent exit window facing the skin thereby adhering the transparent exit window to the transparent foil,
• wherein the transparent foil is more hydrophobic than the transparent exit window.

A method for optical coupling of an incident light beam from a device for light based skin treatment into a skin, the method comprising:

• applying a transparent mixture of a polar substance and an apolar substance to an inner surface of a transparent foil not facing the skin,
• applying a fluid to an outer surface of the transparent foil facing the skin,
• applying the transparent foil as a separate replaceable covering arranged and configured to be pulled over at least a transparent exit window,
• pressing said transparent exit window to the transparent foil covering thereby adhering the transparent exit window to the transparent foil,
• wherein the transparent foil is more hydrophobic than the transparent exit window.