A method for producing a nanoparticle to separate a diketopyrrolopyrrole pigment includes separating an \u03b1-type diketopyrrolopyrrole pigment nanoparticle having high crystallinity by carrying out separation of the diketopyrrolopyrrole pigment and crystal type transformation to the \u03b1-type with substantially a single step. The optical element may be used with at least two wavelengths, e. The housing has at least a first part and a second part which is movable relative to the first part to open the enclosure.