Random laser

A random laser is a laser that uses a highly disordered gain medium. A random laser uses no optical cavity but the remaining principles of operation remain the same as for a conventional laser. Random laser action has been observed in many different media, including semiconductor powder, nanostructured and non-nanostructured thin films, laser dyes, ceramics and many more.

Developments in nanoparticles have demonstrated that large amounts of optical scattering can occur when photons are incident. In this way, light can be diffused around a medium in much the same way as it is on white paint and in clouds.

If nano particles are embedded in an optical gain medium, for example, zinc oxide (UV emission - bandgap 3.3 eV), light from a pump source ( e.g. frequency-tripled Nd:YAG laser) will induce spontaneous emission of light at around 350 nm within the gain medium. These spontaneously emitted photons will then stimulate other radiative transitions in the gain medium to take place, unleashing yet more photons. This is, in many ways analogous to the chain reaction that occurs in the fission of neutrons in a nuclear reactor and has been referred to by R.H. Dicke (reaching for a metaphor) as an "optical bomb".

Anderson localization is a well-known phenomenon which occurs when electrons become trapped in a disordered metallic structure and this metal goes through a phase transition from conductor to insulator. These electrons are said to be Anderson Localized. The conditions for this localization are that there is a high enough density of scatters in the metal (other electrons, spins, etc.) to cause free electrons to follow a single looped path.

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