Process and apparatus for locally polymerizing a starting material by dual color photopolymerization and method for volumetric printing of a shaped body

A process for locally polymerizing a starting material by dual color photopolymerization, comprising:

• providing a polymerizable starting material containing photoinitiator molecules which can be converted by sequential optical excitation into a reactive state in which the photoinitiator molecules locally trigger polymerization of the starting material;
• and
• photopolymerizing the starting material in a local volume by irradiating light of a first wavelength and light of a second wavelength, different from the first wavelength, into the local volume, whereby in the local volume
• the photoinitiator molecules are converted, due to the absorption of the light of the first wavelength, from an initial state in which the photoinitiator molecules substantially do not absorb the light of the second wavelength, into an intermediate state with changed optical properties compared to the initial state, such that the photoinitiator molecules in the intermediate state absorb the light of the second wavelength;
• and
• the photoinitiator molecules are transferred from the intermediate state to the reactive state due to the absorption of the light of the second wavelength, which triggers the polymerization locally;
• wherein the polymerizable starting material further contains a solvent, wherein the solvent is water.