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Re: Quantum question?



I see the connection between frequencies and time. As I told Leigh, I guess
I have to think about how time relates to spectral emission lines. I have a
hard time seeing how emission lines that are broad when measured through a
short time interval become sharp when measured over a long time interval.

They don't. Emission lines have a width (the natural linewidth) that
is related by the uncertainty principle to the lifetime of the upper
energy level. I think circumstance where measurement time limits the
line narrowness are rare. More common is the case in which other
processes (usually nonradiative) broaden the line. High pressure may
broaden an emission line in a gas discharge because collisions are
shortening the upper state lifetime. (This is distinct from doppler
broadening, of course).

A single photon doesn't have a linewidth. Linewidth pertains to the
distribution of energies in an ensemble of photons.

Leigh