Double the Photons for Selectivity

Significance

Spatially resolved photopolymeri­zations enable the formation of objects and patterns and will be of increasing importance in the future. Like conventional photolithography, the resolution in some cases is limited by the inability to confine light with lenses to dimensions less than half its wavelength. Nonlinearity in an absorption process can be used to create superior resolution and there have been many examples of using simultaneous two-photon absorptions to create polymers. A drawback is that this process requires the design of special two-photon-absorbing chromophores and/or high-intensity lasers. However, in this case the method involves sequential absorption of hν (1) and hν (2) and in this way can be triggered with less intense sources.