Highway ticket treated with ninhydrin. (a) Inspection performed in the visible region. (b) Inspection performed by exploiting the luminescence of the thermal paper (input radiation: 400–640 nm, longpass filter on the emitted radiation: >695 nm).
Highway ticket treated with ninhydrin. (a) Inspection performed in the visible region. (b) Inspection performed by exploiting the luminescence of the thermal paper(input radiation: 400–640 nm, longpass filter on the emitted radiation: >695 nm).