Can anybody explain briefly about two photon absorption and how the focus spot becomes small in two photon lithography than single photon lithography. There is plenty of literature but I am not finding a suitable explanation for why the absorption is dependent on the square of the intensity. If so, why is it weaker than the single photon absorption.
http://en.wikipedia.org/wiki/Two-photon_absorption.
See:
“Two-Photon Photopolymerization and 3D Lithographic Microfabrication” by Hong-Bo Sun and Satoshi Kawata
http://nathan.instras.com/MyDocsDB/doc-712.pdf
“Nanofabrication using Two-photon Polymerization and Direct Vectorial Writing” by Puskal Kunwar
http://dspace.cc.tut.fi/dpub/bitstream/handle/123456789/20657/kunwar.pdf?sequence=3
See also:
“Two-Photon Polymerization Fabrication of Doped Microstructures” by Daniel S. Correa, Leonardo De Boni, Adriano J. G. Otuka, Vinicius Tribuzi and Cleber R. Mendonça
http://www.intechopen.com/download/get/type/pdfs/id/38898
Two-photon absorption is a process related to the change in the electronic state of an atom or molecule, which is excited from a lower energy level n (ground state, in the most of cases) to a higher electronic state n +1, absorbing simultaneously two-photon of same energies (called “degenerate process”) or different energies (called “non-degenerate process”).
Two-photon absorption (2PA) is a nonlinear optical process in which a molecule "simultaneously" absorbs 2 photons to reach an excited state. Often, these photons are quite low in energy, so low that the molecule's typical absorption spectrum shows essentially no absorbance. This is because the extinction coefficient (magnitude of the transition dipole) is very small. The absorption is said to occur through transient (virtual) states that have extremely small lifetimes, on the order of about 5 femtoseconds. Unless another photon strikes the molecule within this lifetime, it simply decays and you don't notice the absorption at all. The intensity of the light source in a UV-Vis spectrometer does not produce light intensely enough for a second absorption to occur at a very high probability. Only with very high intensity light (laser source) does it become probable enough to observe 2PA because the second photon has to strike the same molecule (whose lifetime is extremely short). For additional information, download the document from the following link and start on page 12.
http://uknowledge.uky.edu/chemistry_etds/22/
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Materials Chemistry