Laser light-----------------------------------emission

These concepts of the classical physics of standing waves have important implications in photophysics, in particular for the understanding of orbital symmetries and laser light emission. In the case of a standing wave the propagation velocity does not exist, and the important relationship defines the wavelengths as a function of the distance between the boundaries and the number of nodes in the wavefunction... 

Laser (Light emission by stimulated emission of radiation), action, with its tremendous phase coherence (Rayleigh scattering), was discovered much later, in 1960 (Section 10.10), but provision for it already existed in Einstein s analysis ... 

In figure 16 a portion of the initial (a) and delayed (b) emission spectra of HMX is shown after irradiation with 248 nm laser light. Emission spectra of RDX are similar [39]. In these initial spectra, CN could be identified superposed onto a continuum. This is in contrast with the emission characteristics of mercury fulminate, which showed CN only after a time delay. No line inversion was observed. 

The acronym LASER (Light Amplification via tire Stimulated Emission of Radiation) defines the process of amplification. For all intents and purjDoses tliis metliod was elegantly outlined by Einstein in 1917 [H] wherein he derived a treatment of the dynamic equilibrium of a material in a electromagnetic field absorbing and emitting photons. Key here is tire insight tliat, in addition to absorjDtion and spontaneous emission processes, in an excited system one can stimulate tire emission of a photon by interaction witli tire electromagnetic field. It is tliis stimulated emission process which lays tire conceptual foundation of tire laser. 

The timing of the emission is clearly dependent on the system in use. For example, if pumping is relatively slow and stimulated emission is fast, then the emergent beam of laser light will appear as a short pulse (subsequent lasing must await sufficient population inversion). This behavior is... 

The reaction path shows how Xe and Clj react with electrons initially to form Xe cations. These react with Clj or Cl- to give electronically excited-state molecules XeCl, which emit light to return to ground-state XeCI. The latter are not stable and immediately dissociate to give xenon and chlorine. In such gas lasers, translational motion of the excited-state XeCl gives rise to some Doppler shifting in the laser light, so the emission line is not as sharp as it is in solid-state lasers. 

LASER, light amplification by stimulated emission of radiation... 

An argon-ion laser is used in some laser light shows. The argon ion has strong emissions at 485 nm and 512 nm. 

Figure 10-15. Output vs. input energy characteristic of our laser device. The horizontal dashed curve indicates the zero line. A clear laser threshold behavior at an excitation pulse energy ol 1.5 nJ is observed. Below the lasing threshold only isotropic phololuminesccncc is entitled. Above threshold the device emits low divergence single mode laser emission perpendicular to the surface, as schematically shown in the inset. The laser light is polarized parallel to the grating lines.

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