On Thu, Apr 28, 2022 at 2:42 AM William Beaty <bi...@eskimo.com> wrote:
> On Wed, 27 Apr 2022, H LV wrote: > > > I have been doing more reading about the history of stimulated > > emission. Einstein formally introduced a quantum version of the concept > in > > 1917. > > "STIMULATED EMISSION!" Oh man don't even get me started. (Too late!) > Saying the words Stimulated Emission, that's like wearing a Susquehanna > hat in an Abbott and Costello bit, and then saying "Niagara Falls" > ...slowly I turned, step by step, INCH BY INCH. > > A very simple classical analog of Stimulated Emission (circuit-based > stimulated emission) ...seems to have been missed by everyone. It's a > part of the "missing physics" of EM wave-absorption by atoms, photon- > destruction, Einstein's fundamental mistakes about photoelectric effect, > as well as being part of the odd "energy-sucking" effects seen with short > resonant antennas. All these topics constitute a single subject, and, > having been missed by Classical physics textbooks, are declared to be > "QM-only phenomena" when they crop up in various places. > > OK, first say we have a classical EM oscillator (a tank circuit hanging in > space,) and it's slowly emitting a small amount of radio waves. Is there > a way to force it to suddenly dump all of its stored energy as a huge > blast of EM radiation? > > Certainly. It's dead-simple stuff. Should be part of every EM textbook. > > But it's not. > > Instead, Stimulated Emission is treated as some rare and unique, QM-only > process, rather than a normal part of basic radio-science. (Similar > treatment is given to the weird behavior of electrically-small resonant > antennas: ignored, except when it crops up as "virtual photon" effects > with atomic resonance, narrow-linewidth photon absorption, > nearfield/evanescent "photon tunneling," etc.) > > I found this paper from 1987 but it is not open access. --------------- https://opg.optica.org/josab/abstract.cfm?uri=josab-4-1-78 Classical stimulated emission Benjamin Fain and Peter W. Milonni Abstract Stimulated emission is formulated in completely classical terms and is shown to occur in general only in nonlinear systems. Our approach is based on the frequency-dependent susceptibility, which in both the classical and quantum-mechanical descriptions is the main characteristic determining whether there is absorption or stimulated emission. By using Bom’s correspondence rule, we derive an expression for the lowest-order quantum correction to the classical susceptibility. --------------------- I want to revisit Rayleigh and Jeans famous classical calculation for the spectral energy distribution from a blackbody that produced the ultraviolet catastrophe. When doing their calculation they required that the electric field on the cavity wall must be zero everywhere for all frequencies. Since the calculation resulted in a physically unrealistic prediction of the spectral energy distribution did it occur to them that the boundary condition was physically unrealistic? How would the calculation change if the electric field were allowed to be frequency dependent? This is a conventional but detailed presentation of Rayleigh and Jeans law for blackbody radiation. https://www.youtube.com/watch?v=rCfPQLVzus4 Harry > Put bluntly, Stimulated Emission works at DC, and obviously applies to > all capacitors. > > If we have a charged capacitor, we can connect it to a resistor, and > remove its energy according to RC time-constant. Or, we can short it out, > and the much shorter RC-constant then depends on the capacitor's internal > impedance, and the micro-ohms of wire resistance (ignoring for the moment > any wave-emission and LC effects.) > > > Or instead, we can force that capacitor to dump out its energy at ANY fast > rate desired, even many orders faster than just shorting it out. > > Simply hook it up to a high-amps constant-current supply. > > But hook it up backwards. > > Before the backwards-connected capacitor can begin to be "charged" by > conneting it to this CC supply, first it has to be discharged to zero > (where the joules in the capacitor are then EMITTED, and they must move > out of the capacitor and into the CC supply.) And clearly we can > discharge this capacitor at ANY rate desired, proportional to the > current-output of the backwards-connected CC supply. > > The discharge-time can easily be orders shorter than any conceivable > natural RC-constant. (The capacitor might possess micro-ohms of internal > resistance, and if it's simply being shorted, have a very short RC time > constant for discharge. But if we apply a huge backwards current, we can > discharge it hundreds of times faster than that, thousands of times, any > speed desired. That's the essence of Stimulated Emission of course: the > max rate of "energy dumping" is determined by the stimulating signal, not > only by the characterists of the energy-storage capacitor (or resonator.) ) > > Pretty cool, eh? > > And, whatever applies to capacitors, also applies to Classical LC tank > circuits hovering in the vacuum. > > An EM-resonator in space, if it contains some stored energy, is slowly > leaking away it's EM energy as radio waves (or even optical photons) at > the LC resonant freq. We can force it to suddenly dump out all of > its energy in any short time desired. Simply blast it with an EM-wave > which has 180deg phase relationship to that oscillator. (This is the same > as connecting a pre-charged capacitor to a HV power supply, connecting it > backwards.) Our tank circuit hovering in space must first discharge all > its stored energy, before it can absorb any energy from the EM waves > striking it. Blast it with extremely high-amplitude waves, and first it > will rapidly "dump" its stored energy ...then quickly fall to zero total > stored energy ...then start rapidly absoring energy from the incoming > waves. (Viewed from the side, it would suddenly output a huge flash of > EM waves, before settling down and becoming a normal absorber.) > > Everyone knows that we can quickly charge up a capaictor using an HV > supply ...and the same applies to LC resonators hooked to HV AC power > supplies tuned to resonate. > > But if the capacitor or the LC resonator already contains some energy, > then we can force a sudden "dumping," by connecting it to our power supply > backwards. > > Oddly, I've never encountered ANYONE discussing these concepts. The > closest have been the few papers about the enormously wide "effective > apertures" seen with short resonant antennas. (And then there's Willis > Lamb's various articles against the photon concept: "Anti-photon.") But > even these papers never discuss a resonant antenna which already happens > to store some oscillations, and then is suddenly hit with incoming waves > at 180deg phase. (The process is directly analogous to taking a charged > capacitor and NOT shorting it out, but instead, hooking it backwards to a > power supply at extremely high cufrent, to force it to "dump energy" at > extremely high rate.) > > --- > > Next, imagine that we have hundreds of tiny LC oscillators (resonators) > floating in space, all "charged up" with oscillations at various > randomized phases. If they're closely spaced, then on average they cannot > emit EM waves, because for every oscillator trying to send out waves at q > phase, there will be a nearby one in the same nearfield-zone trying to > emit at q+180deg phase. The fields cancel out, so emission isn't > possible. This is our model of a pumped fluoresecent material, with only a > "statistical tail" of EM waves able to escape from the "medium." > > > What happens when all these oscillators are suddently hit with > "Stimulating" radiation: an extremely powerful EM wave? Some start > absorbing, and add more energy to their existing oscillations. Others > will suddenly dump out their stored energy in an intense blast! Those are > the ones which happened to be out of phase with the incoming EM waves. > > On average, will our "laser medium" emit more joules than it absorbs? Can > it amplify the incoming wave? And, will we see any "Rabi oscillations?" > (Classical ones of course, not QM-only photon effects.) > > PS > > I find Rabi Oscillations to be fascinating, because top experts claim that > they're a QM-only phenomenon, yet any brief examination shows them to be > identical to the "slow-beats oscillation" of two coupled mechanical > pendulua ...but in the case of optical Rabi oscillations, one pendulum is > positioned far away, and is only "coupled" to the other by illuminating it > with some of its emitted EM radiation. Heh, imagine that two mechanical > pendula are very distant, and coupled only by subsonic sound waves. Each > one considered alone, should then mysteriously build up its swinging > motion, then diminsh to zero, then build up again, over and over. If we > don't know about the existence of the other distant pendulum, we'll give > these strange slow modulations of pendulum-swinging a new name: Rabi > oscillations! (And next, pretend that they're a mysterious effect limited > to QM systems, atoms and photons, or only seen in mechanical systems > chilled near 0deg K, etc. And, if you should ever notice the phenomenon > of over-coupled macro-sized pendulums, be sure to never, never label it > with the name "line-splitting.") > > > > > (((((((((((((((( ( ( ( ( (O) ) ) ) ) )))))))))))))))) > William J. Beaty http://staff.washington.edu/wbeaty/ > beaty, chem washington edu Research Engineer > billb, amasci com UW Chem Dept, Bagley Hall RM74 > x3-6195 Box 351700, Seattle, WA 98195-1700
