Skin treatment device providing optical coupling to skin tissue

A skin treatment device for light-based treatment of skin tissue, the skin treatment device comprising:

• a light source constructed for emitting treatment light,
• an optical system constructed for focusing the treatment light along an optical axis to a focus position inside the skin tissue, and
• an indenter comprising a skin contact surface having an aperture (A1, An) at a distance from the optical system for allowing the treatment light to be focused through the aperture (A1, An) into the skin tissue, the indenter and the aperture (A1, An) being configured and constructed for generating, in a cross-section of the aperture (A1, An) taken along the optical axis (OA, OAn) and along a cross-section direction wherein the aperture (A1, An) has a width dimension (d1, dn), a maximally curved protrusion of skin tissue freely protruding through the aperture (A1, An) towards the optical system when the indenter is pressed against the skin surface of a specific skin type with a pressure exceeding a predefined pressure above which for the specific skin type the freely protruding curved protrusion remains constant, a skin surface of said maximally curved protrusion having a radius of curvature (RC, RCn) at an intersection with the optical axis (OA, OAn),
• the optical system being configured and constructed for generating a focused beam of the treatment light having, in said cross-section of the aperture (A1, An) at said intersection, a wave front (WF) with a radius of curvature ranging between 75% and 125% of said radius of curvature (RC, RCn) of the skin surface of said maximally curved protrusion.