Synopsis The evaluation of sun-product efficacy, with laboratory solar simulators or in actual sun, implicates clinical and subjective assessment of the various skin responses in terms of wavelengths constitutive of solar light. These photobiological responses vary according to skin types and particularly to basic skin melanic content, i.e. with skin colour. Now, the instrumental measurement of live skin colour has become easier to perform, fast and reliable. Based on the standard CIE-L*a*b* colour system and correlated with the human eye, this technique was used to define the skin colour domain of the caucasian population, to propose a skin colour classification, and then to objectively follow, over a three week period, the dynamics and kinetics of tanning induced by UVB, UVA and UVB +/- A multi-exposures on the three skin categories. The specific directions in the three-dimensional L*a*b* colour space of the tanning components, i.e. erythema, immediate pigmentation and constitutional melanization, as well as the resulting tanning pathways, were analysed and defined in the three-dimensional colour space, using a vectorial method. The UVB, UVA and UVB +/- A tannings were differentiated by their intensity, their hue and especially their lasting capacity: UVA tanning clearly appeared more lasting than UVB. In addition, the UVA*UVB interaction on tanning intensity was not found to be significant. With the skin colour classification and the tanning models, this comprehensive study supplies a basic tool for the colorimetric interpretation of the skin phenomena involved, provided that this interpretation is always considered in the three dimensions of the colour space. It also suggests some useful practical applications for sun product formulation and evaluation.

The results show PPD to be a stable end point inducible by all the UVA wavelengths, not affected by fluence rate, i.e. a reliable endogenous UVA dosimeter in the skin.

Efficient repetitive passive Q switching of a cladding-pumped Er -Yb fiber laser has been demonstrated by use of an external-cavity configuration containing a Co 21 : ZnS crystal as a saturable absorber. Energies of as much as 60 mJ in pulses of durations as short as 3.5 ns (FWHM), corresponding to a peak power of .10 kW, have been generated, and the maximum slope efficiency with respect to the absorbed pump power was 13%. Using a bulk diffraction grating in the Littrow configuration to provide wavelength-selective feedback, we tuned the passively Q-switched fiber laser over 31 nm from 1532 to 1563 nm. The prospects for further improvement in performance are discussed. © 2002 Optical Society of America OCIS codes: 060.2320, 140.3480, 140.3540, 140.3510, 140.3600. Over the past decade, progress in the development of efficient diode-pumped, pulsed solid-state lasers operating in the eye-safe wavelength regime near 1.5 mm has been dramatic, fueled by the needs of a variety of scientific, industrial, and defense applications. For some of these applications (e.g., range finding and remote sensing) the requirement for short pulses (a few nanoseconds) has led to the development of compact Er-Yb-doped glass microlasers with active or passive Q switching. By virtue of their very short cavity lengths (typically a few millimeters), these lasers can generate pulses of ,8-ns duration and .3-mJ energy. 1An alternative method for producing pulsed output in the 1.5-mm spectral range is to Q switch an Er -Yb-codoped fiber laser. This approach has the potential attraction that output powers should be scalable to much higher levels without degradation in beam quality by the use of a double-clad fiber design and cladding -pumping. To simplify the resonator design and eliminate the need for external Q-switching electronics, passive Q switching of single-clad Er-doped fiber lasers has also been attempted with a liquefying gallium mirror, 9 a semiconductor saturable absorber, 10 and a Co 21 :ZnSe crystal as the saturable absorber.11

The calibration procedure proposed shows threshold PPD, used as an end point in a UVA-PF test method, to be a reliable endogenous dosimeter for UVA radiation that enters the skin.

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