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.)
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
