FIELD : medicine.SUBSTANCE : non-invasive device for treatment of skin by wrinkle reduction in skin with laser light. Device comprises : an optical system having a laser light source for generating a light beam, being configured such that, in use, light beam exits the device and impinges on an outer surface of the skin to be treated; opening disposed such that, in use, light returning from the skin enters the device as a measurement light beam; first and a second intensity detection channel configured and arranged to detect the intensity in, respectively, a first and a second bandwidth range of the measurement light beam; processor connected to the first and the second intensity detection channel, wherein the processor being configured to determine the occurrence of both laser induced optical breakdown and second harmonic generation at the position of the treatment location, based on the intensities detected by the first and the second intensity detection channel. Wherein the first bandwidth range and second bandwidth range comprises a light wavelength generated in skin as a result of laser induced optical breakdown, first bandwidth range comprises the second harmonic generation wavelength of the laser light source, second bandwidth range is adjacent to the first bandwidth range, and the second bandwidth range excludes the second harmonic generation wavelength of the laser light source. Wherein the optical system is configured to focus, in use, the light beam at a position of a treatment location inside the skin, whereby laser induced optical breakdown is induced at the position of the treatment location.EFFECT : group of inventions provides higher efficiency of reducing skin wrinkles.11 cl, 3 dwg