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Re: [FT] Vector Move question

From: Tom Anderson <thomas.anderson@u...>
Date: Tue, 3 Aug 1999 21:53:20 +0100 (BST)
Subject: Re: [FT] Vector Move question

On Sun, 1 Aug 1999, Laserlight wrote:

> >Without wanting to go through all of that again, I feel obliged to
> >
> >>According to the printed rules, it's legal.  However, it is also
> >>Exceptionally Cheesy. 
> Beth responded
> >Hey I wouldn't say that! You guys got your double screens, strong
> >armour and even stealth (!!) I've got my good old FSE thrust... I'll
> >PS2TS3MD6 and get the heck out of here before you all kick my butt
> >dissenting ;)
> Elementary Physics Lesson #1: You Can't Outrun a Laser.

Advanced Physics Lesson #1: Oh Yes You Can

the trick is to make sure the laser is going through a highly cunning
medium ...

--- begin quote ---
source: Nature 397, 559 - 560 (1999)
title: Slow light in cool atoms
author: Jon Marangos
copyright: Macmillan Publishers Ltd. 1999

An experiment with atoms at nanokelvin temperatures has produced the
remarkable observation of light pulses travelling at velocities of only
m s-1. The large optical nonlinearities seen in this system may open up
new opportunities in quantum optics.

In our usual understanding, the speed of light, c, is the absolute top
speed in the Universe at 3 108 m s-1 in a vacuum. So observation of
pulses propagating at a speed no faster than a swiftly moving bicycle,
described by Hau et al.1 on page 594 of this issue, comes as a surprise.
We know that light can be slowed to a modest extent in refractive and
transparent media, for example water and glass, to velocities typically
factor of 1.5-2.0 times slower than c. But there is a limit to how much
light can be slowed in normal optical materials, because the larger
refractive index associated with slower propagation is inevitably
accompanied by increased light absorption.

Under special circumstances, however, this limit can be overcome -- that
is, a perfectly transparent medium can be created in which the speed of
light is slowed enormously. The systems in question are laser-dressed
atomic media that acquire new optical properties because light does not
interact directly with atoms but with a system composed of atoms plus
laser field. This requires the preparation of laser-dressed atoms (see
for the technical details) to create what is termed electromagnetically
induced transparency, in which quantum interference leads to the
cancellation of absorption2. In this new kind of system, the dispersive
(or refractive) properties of the medium -- including the velocity of
propagation of an optical pulse -- become independent of absorption3.
example, Steve Harris and colleagues4 at Stanford have used coherently
prepared lead atoms to reduce the propagation velocity of a resonantly
tuned light pulse to c/165. To achieve even slower pulse velocities,
atoms are required because, to maximize the quantum interference effect,
the thermal motion must be small.

--- end quote ---

lifting copyrighted text from a journal is somewhat dodgy, but i believe
this qualifies as fair use.


ps i know neither of these were lesson #1; we really should put together
GZG-L Physics Primer at some point :)

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