Aug 15 2013
Multi-photon absorption is a technique that is widely used in atomic and molecular physics to determine the properties of materials. Multi-photon absorption is a non-linear process, and can be used as a type of non-linear spectroscopic measurement. Non-linear spectroscopy is based on the interaction of a pulsed light source with a non-linear medium.
The absorption rate of n photons is proportional to the nth power of the photon flux density. When a medium absorbs multiple photons, it will move to an intermediate excited electronic state. This article will elaborate on the working, experimental set up and applications of multi-photon absorption process.
Experimental Set Up
Multi-photon absorption in caesium can be observed by using a DCM dye laser. Multiphoton absorption maybe viewed as the absorption of two entangled photons that are generated by the spontaneous parametric down conversion process. In this process, a high power laser is passed through a non-linear medium, resulting in the generation of a pair of entangled photons. These pairs of photons are absorbed by an absorber.
Working
When a non-linear medium absorbs multiple photons simultaneously, the atom will proceed to an intermediate energy level. The atom will return to its original state by emitting radiation. The lines emitted by the medium are scanned using a laser, a DCM dye laser. Various ionization states could be identified by observing the transition lines.
Some of the observations of multi-photon absorption are listed below:
- Emission spectrum is the same as 1-p
- Emission quantum yield remains the same
- Fluorescence lifetime remains the same
- Spectral positions nominally scale for the same transition
Applications
Some of the applications of multi-photon absorption process are listed below:
- Molecular spectroscopy
- 3D photo polymerization
- Optical power limiting
- Optical data storage.
Sources and Further Reading