RE: starship-design: Casimir-Foreward balloon

[Zenon Kulpa <zkulpa@zmit1.ippt.gov.pl>]

> From owner-starship-design@lists.uoregon.edu Fri Jan 14 04:00:37 2000
> From: "L. Parker" <lparker@cacaphony.net>
> 
> > > From owner-starship-design@lists.uoregon.edu Thu Jan 13 20:05:32 2000
> > > From: "N. Lindberg" <nlindber@u.washington.edu>
> > >
> > > 	I have a question about the 'phosphor' inside the balloon, and
> > > about phosphorescent materiels in general.
> > >
> > As far as I know:
> >
> > > Apparently, a phosphor absorbs
> > > a high-energy photon, and re-emits low energy photons.
> > >
> > Sometimes other way around, but rarely.
> > Also, there is phosphorescence and luminescence.
> > The difference is in the delay between absorbing
> > (some energy, e.g., a photon) and emitting a photon.
> > Phosphorescent materials have long delay (even days),
> > so they shine long after the excitation ended
> > (e.g., materials glowing in the dark) while luminescent
> > materials stop to radiate almost immediately after
> > the excitation stopped.
> 
> First, lets straighten out the terminology...
> 
I would like to thank you for correcting my terminology, but...

> "Luminescence" is an emission of light such as "fluorescence" or
> "phosphorescence" which is not directly attributable to heat as is for
> instance "incandescence". "Fluorescence" is the property possessed by some
> materials of absorbing radiation at a _particular_ wavelength and then
> emitting it as _white_ light 
>
? Usually fairly monochromatic or with few narrow frequency bands;
to obtain white (as in fluorescent white light tubes) a special mixtures
of different materials emitting at different bands must be used.

> while the stimulus, the radiation source, is
> still active. Fluorescence is distinct from "phosphorescence" which merely
> means the emission of light without any perceptible heat. Phosphorescence
> may be caused by many different stimuli such as chemical reactions or
> radiation. Luminescence includes both of these phenomena and fluorescence
> may include phosphorescence or may not.
> 
... your explanation confuses me even more...
Certainly, it seems to be that in English the terminology 
in this area goes differently than in Polish, hence my confusion...
Anyway, this is not very important in this particular case,
so let us drop it for a while.


> [CLIP]
> 
> > > What is the typical energy difference/proportion between
> > > absorbed & emitted light.
> > >
> > Ehem, what means "typical" here?
> > There is the whole range o proportions, byt of course,
> > always there is less energy emitted than absorbed
> > (usually much less - the efficiency of the process is rather low).
> >
> > > Finally, is any energy left over?
> > >
> > Yes, usually a significant percentage (as stated above).
> > The sources of loss:
> > - not all exciting photons are absorbed (some go through,
> >   some are reflected);
> > - still some incoming photons are absorbed in other ways
> >   (eg., in inner electron layers) and are converted to heat;
> > - the emitted photons are of lower energy (longer wavelength),
> >   or - where it does not apply - are of lower energy than the sum
> >   of energies of those photons which were used in the process
> >   of generating them;
> > - falling down of electrons not always occurs along the standard
> >   route, so that they may emit other photons than desired - often
> >   those that are then easily (re)absorbed and converted to heat;
> > - the "desired" photons may get absorbed and converted to other ones
> >   or to heat before they manage to leave the material.
> 
> As the question is stated, yes there may be a difference between "absorbed
> radiation" and "emitted light". However, there is never any difference in
> the energy of the system, as in "left over energy". Energy is always
> conserved. Some may be converted to other forms of energy besides "light"
> but all the energy absorbed by the material is eventually emitted in some
> form.
> 
> I suppose you could say that in an extreme case, say a particle accelerator,
> you could theoretically insert enough energy to permanently raise the energy
> of the material, by transmuting it into a different material. But the total
> energy of the system still remains the same even then.
> 
Of cource it is all true - what I called "loss of energy" refers only
to the difference beween total energu of the stimulating radiation 
and the total energy of "usable" output radiation - i.e., that 
of the light of fluorescence (which is usually either fairly 
monochromatic or contains only a few narrow bands of wavelengths).
The rest is of course emitted sooner or later in some form
(or stored in the material in some way).

-- Zenon Kulpa