Absorption and fluorescence in Rb sub-micron cell on D2 line have been studied when the thickness L varies in the range of 0.5 λ - 3.5 λ, and the laser intensity is 0.1 - 1 W/cm2 (λ = 780 nm, λL ~ 5 MHz). When L = (2n +1) λ/2 (n-integer) and I ~ 0.1 W/cm2, revival of peaks of Dicke-type coherent narrowing effect with some modification of the spectra (as compared with low intensity regime) are still observable. The experimental results obtained at I ~ 1 W/cm2 for L = λ/2 show that there are no "dips" of a reduced absorption in the spectra, though there is a strong spectral broadening of the absorption (and fluorescence), as well as a reduction of the absorption (in contrast, I ~ 1 mW/cm2 is sufficient to create the dips when L = λ). Probably, this is caused by a strong Dicke narrowing regime when L = λ/2. Several additional differences of fluorescence and absorption spectra behaviour at high intensities are revealed.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.