First Principles Laser Theory. Alfred D. Stone - Yale University - DMR 0408638.
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Alfred D. Stone - Yale University - DMR 0408638
The first lasers were invented in 1960. By 1963-4, Haken and Lamb had developed the standard theory of the light output of a laser, known as semiclassical laser theory (SCLT). The theory is based on the coupled non-linear Maxwell-Bloch equations, which depend on time and space. SCLT was never developed into a predictive laser theory; it showed how a lasing might work in general, but did not allow prediction of how a specific laser did work: how much light it emitted for a given input power (pump),what frequencies it emitted, and what spatial pattern of light the laser produced. In condensed matter theory, self-consistent equations have been developed to allow prediction of electronic properties from a few simple inputs. The goal of this research was to do the same for lasers.
In 2006, Stone and coworkers derived such an “ab initio” (AI) laser theory, which predicts all stationary lasing properties from simple inputs, based on a new self-consistent time-independent formalism. In 2008 they applied the formalism to random lasers, a new laser which defied previous approaches -Their results appeared in Science, 320, 643 (2008). Applications of the AI laser theory to other novel micro and nanolasers are in progress.
Tureci,Ge, Rotter, Stone, Science, May 2, 2008
In a conventional laser light bounces back and forth between mirrors and is amplified by the gain medium. Its frequencies are set by the mirror spacing. In a random lasers there are no mirrors, light diffuses, scattering from nanoparticles and then escapes in all directions. There is no simple principle determining the emitted frequencies and no simple means of calculating them just from the configuration of nanoparticles (passive cavity).
Our new theory allows us to calculate lasing frequencies and intensities for this non-conventional laser (see bottom right). Different electric field patterns are found for each frequency (false color images). The frequencies are stable under different pump conditions (dashed and solid lines), but the intensities vary greatly, as found experimentally.
The different lasing “modes” strongly interact making the calculations difficult.
Random lasers have been proposed for applications as unique identifiers (labels), displays and in medical imaging.