Process for generation of free superacid and for imaging, and imaging medium for use therein

A process for generation of free superacid, which process comprises:

• providing a medium containing a mixture of a superacid precursor and a dye capable of absorbing actinic radiation of a first wavelength which does not, in the absence of the dye, cause decomposition of the superacid precursor to form the corresponding superacid, the superacid precursor being capable of being decomposed by actinic radiation of a second wavelength shorter than the first wavelength;
• irradiating part of the medium with actinic radiation of the first wavelength, thereby causing, in the irradiated part of the medium, absorption of the actinic radiation, and decomposition of part of the superacid precursor, without formation of free superacid but with formation of a protonated product derived from the dye;
• and
• thereafter irradiating a larger portion of the medium with actinic radiation of the second wavelength, thereby causing, in the part of the medium exposed to the radiation of both the first and second wavelengths, decomposition of part of the remaining superacid precursor, with formation of free superacid without generation of free superacid in the part of the medium exposed to the radiation of the second wavelength but not to the radiation of the first wavelength.