> I have been doing more reading about the history of stimulated > emission. Einstein formally introduced a quantum version of the concept in > 1917. > Therefore you might think that it is only possible in a quantum theoretical > context. However, subsequent mathematical work has shown that a form of > stimulated emission can also arise in a classical (pre-quantum) setting > when a suitable model of the atom is used.
The key point about stimulated emission is that it exploits the suspension of superposition exclusion to enable an aggregate system to cohere under a unitary wavefuntion; the corollary effect being coherent absorption, such that the initial plasma system can be classically described right up to the population inversion: from which point all electrons are bouncing between peak energy and stable bottom, emitting and absorbing essentially the same photons in sync.. ..so the quantum / classical threshold there is Pauli exclusion; the spontaneous photomultiplication resulting from collective coherence of the electron population is a pretty fundamental kind of 'resonance', not your average harmonic oscillator. On this key point about coherent absorption as well as emission, see Green at al "Limiting photovoltaic monochromatic light conversion efficiency" 2001, noting that in PV cells for which recombination is mainly radiative, a stimulated emission regime could take efficiency arbitrarily close to the Carnot limit; his team down in Oz are currently up to ~70% - again, for monochromatic (basically laser) light - with increasing applications in ie. wireless power transmission, electrical isolation / firewalling etc., and obvs much greater range (albeit limited to LoS) than classical inductive transmission techniques. A stimulated emission mode / regime is an inherently quantum-classical system, a unique means of corralling quantum systems distinct from Faraday and Maxwell et al; the system's propensity to begin lasing a direct consequence of the quantisation of energy & momentum: in the tensioned 'population inversion' state, ideally at least, a single photon of further input energy will inevitably trigger a cascade of absorption and emission because there's nowhere else for this conserved quantised energy to go, ie. further input energy catalyses a cyclic phase transition between high and low-energy states, because the transitions are quantised, and because a whole bunch of fermions are behaving as a kind of extended quasi-boson, holding the same quantum-energy states at the same time. It's that force-feedback dynamic, like a turbine, generating this low-entropy livewire state of perfect photoelectric synchrony.. coherent emission AND absorption, en masse.. On a bit of a tangent perhaps, but in his later years GC Huth posited that the retinal cells of the fovea may form a kind of phase-conjugate mirror, which may have thought-provoking implications for ie. the nature of eye contact between sentients, optic nerves essentially being extensions of cortex: what if electrons in remote rhodopsin discs are entangled by the same photons? 'A twinkle in the eye'.. 'windows on the soul'.. (woo-wavy hands)
