Probably the first instance of a photoinduced state is described for the organic molecular compound TTF-CA, which turns from neutral to ionic species as a result of excitation by laser pulses. However, a similar transformation is also possible by the application of pressure, so strictly speaking the photoinduced transition is not to a hidden state under the definition given in the introductory paragraph. A few further examples are given in ref. Photoexcitation has been shown to produce persistent states in vanadates and manganite materials, leading to filamentary paths of a modified charge ordered phase which is sustained by a passing current. Transient superconductivity was also reported in cuprates.