Optical radiation patterns at two wavelengths, an “imaging” wavelength and a “masking” wavelength, are superimposed on a photochromic layer, wherein the masking wavelength induces optical absorbance in the layer, allowing the imaging wavelength to transmit only through narrow transmittance zones where the masking-wavelength radiation has an optical null. The patterns are preferably formed as a focal-point array. At each focal point a focused-radiation spot at the imaging wavelength is superimposed with an annular-radiation spot at the masking wavelength. The spots may be generated by an array of microlenses with focal points proximate the layer. (Several novel types of dual-wavelength microlenses are disclosed.) Alternatively, the focused-radiation spots may be generated in separate optical paths for the two wavelengths, and optically combined at the photochromic layer by means of beam-combining and projection optics. The radiation patterns can also comprise full-field images, which are formed by separate photomasks for the two wavelengths.