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size=2 face=Arial>Folks,</FONT></DIV></DIV>
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size=2 face=Arial>I have become fortuitously aware of an old trick in the lamp
industry that is now sometimes called “light recycling” – with the goal of
enhancing the optical brightness of light sources.</FONT></DIV></DIV>
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size=2 face=Arial>Remember, brightness = power / area in transverse phase
space</FONT></DIV></DIV>
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size=2 face=Arial>(although the opticians don’t generally say it this way,
perhaps using the buzzword “etendue” instead of “area in transverse phase
space”)<BR></FONT></DIV></DIV>
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size=2 face=Arial>In our project, we try to increase the brightness by
“cooling”/shrinking the area in transverse phase space.</FONT></DIV></DIV>
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size=2 face=Arial>The opticians’ trick is to “recycle” the light so that one
photon gets counted many times in the same area in phase space, effectively
increasing the power, while leave the emittance the same.</FONT></DIV></DIV>
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style="FONT-STYLE: normal; DISPLAY: inline; FONT-FAMILY: 'Calibri'; COLOR: #000000; FONT-SIZE: small; FONT-WEIGHT: normal; TEXT-DECORATION: none"><FONT
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size=2 face=Arial>The historical way of doing this (dating back at least to
1936) involves a cylindrical cavity lined with a phosphor (i.e., a fluorescent
lamp) with a small slit in the phosphor to let light out.</FONT></DIV></DIV>
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size=2 face=Arial>A photon has only a small probability P to escape out the slit
directly after being emitted by the phosphor.</FONT></DIV></DIV>
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size=2 face=Arial>Generally, the photon hits another region of the phosphor, is
absorbed, and then re-emitted. [The cavity can be lined with a reflector
to assist in this process.]</FONT></DIV></DIV>
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size=2 face=Arial>On average, the photon bounces around N = 1 / P times before
it escapes through the slit.</FONT></DIV></DIV>
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size=2 face=Arial></FONT> </DIV></DIV>
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size=2 face=Arial>Hence, the steady-state emission of photons by the phosphor
surface is N times greater than if the photons flew away on their first emission
– as holds for an ordinary fluorescent lamp.</FONT></DIV></DIV>
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size=2 face=Arial></FONT> </DIV></DIV>
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size=2 face=Arial>The net effect is that the light coming out of the slit is N
times brighter than the light from an ordinary fluorescent bulb of the same
output power.</FONT></DIV></DIV>
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size=2 face=Arial></FONT> </DIV></DIV>
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size=2 face=Arial>The brightness has been enhanced N-fold (with no emittance
reduction) to the extent that the absorption and re-emission involves no
losses.</FONT></DIV></DIV>
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size=2 face=Arial></FONT> </DIV></DIV>
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size=2 face=Arial>[I think the lamps in Xerox machines and scanners are of this
type.]</FONT></DIV></DIV>
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size=2 face=Arial></FONT> </DIV></DIV>
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size=2 face=Arial>I’ve written up a pedagogic note on this:</FONT></DIV></DIV>
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style="FONT-STYLE: normal; DISPLAY: inline; FONT-FAMILY: 'Calibri'; COLOR: #000000; FONT-SIZE: small; FONT-WEIGHT: normal; TEXT-DECORATION: none"><A
title=http://puhep1.princeton.edu/~mcdonald/examples/lamp.pdf
href="http://puhep1.princeton.edu/~mcdonald/examples/lamp.pdf">http://puhep1.princeton.edu/~mcdonald/examples/lamp.pdf</A></DIV></DIV>
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size=2 face=Arial></FONT> </DIV></DIV>
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face=Arial><FONT
size=2>--------------------------------------</FONT></FONT></DIV></DIV>
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face=Arial><FONT size=2>This trick seems different from what we do to enhance
the brightness of particle beams.</FONT></FONT></DIV></DIV>
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face=Arial><FONT size=2></FONT></FONT> </DIV></DIV>
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face=Arial><FONT size=2>However, a comment by Fred Mills, dated 9/98, near the
bottom of my web page</FONT></FONT></DIV></DIV>
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style="FONT-STYLE: normal; DISPLAY: inline; FONT-FAMILY: 'Calibri'; COLOR: #000000; FONT-SIZE: small; FONT-WEIGHT: normal; TEXT-DECORATION: none"><FONT
face=Arial><A title=http://puhep1.princeton.edu/~mcdonald/mumu/physics/
href="http://puhep1.princeton.edu/~mcdonald/mumu/physics/">http://puhep1.princeton.edu/~mcdonald/mumu/physics/</A></FONT></DIV></DIV>
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face=Arial><FONT size=2>has me wondering if part of the effect of the “Piccione
lip” seen on p. 4 of</FONT></FONT></DIV></DIV>
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style="FONT-STYLE: normal; DISPLAY: inline; FONT-FAMILY: 'Calibri'; COLOR: #000000; FONT-SIZE: small; FONT-WEIGHT: normal; TEXT-DECORATION: none"><A
title=http://puhep1.princeton.edu/~mcdonald/mumu/physics/lichtenberg_mura-110.pdf
href="http://puhep1.princeton.edu/~mcdonald/mumu/physics/lichtenberg_mura-110.pdf">http://puhep1.princeton.edu/~mcdonald/mumu/physics/lichtenberg_mura-110.pdf</A><FONT
size=2 face=Arial> </FONT></DIV></DIV>
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size=2 face=Arial>was to use multiple scattering in the “lip” to kick some
particles into a desired area of phase space.</FONT></DIV></DIV>
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size=2 face=Arial></FONT> </DIV></DIV>
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size=2 face=Arial>That is, perhaps we can say that ionization cooling also
includes a small effect equivalent to the opticians’ trick of “light
recycling”.</FONT></DIV></DIV>
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size=2 face=Arial></FONT> </DIV></DIV>
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size=2 face=Arial>What do you think?</FONT></DIV></DIV>
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size=2 face=Arial></FONT> </DIV></DIV>
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size=2 face=Arial>--Kirk</FONT></DIV></DIV>
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size=2 face=Arial></FONT> </DIV></DIV>
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style="FONT-STYLE: normal; DISPLAY: inline; FONT-FAMILY: 'Calibri'; COLOR: #000000; FONT-SIZE: small; FONT-WEIGHT: normal; TEXT-DECORATION: none"><FONT
size=2 face=Arial>PS The opticians are after big game = use of such tricks
to make better solar energy concentrators for photovoltaic energy generation (or
even just heating water).</FONT></DIV></DIV>
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style="FONT-STYLE: normal; DISPLAY: inline; FONT-FAMILY: 'Calibri'; COLOR: #000000; FONT-SIZE: small; FONT-WEIGHT: normal; TEXT-DECORATION: none"><FONT
size=2 face=Arial></FONT> </DIV></DIV>
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style="FONT-STYLE: normal; DISPLAY: inline; FONT-FAMILY: 'Calibri'; COLOR: #000000; FONT-SIZE: small; FONT-WEIGHT: normal; TEXT-DECORATION: none"><FONT
size=2 face=Arial>In the past, such efforts have not involved brightness
enhancement, but only clever rearrangement of light in phase space (as in
Winston cones).</FONT></DIV></DIV>
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style="FONT-STYLE: normal; DISPLAY: inline; FONT-FAMILY: 'Calibri'; COLOR: #000000; FONT-SIZE: small; FONT-WEIGHT: normal; TEXT-DECORATION: none"><FONT
size=2 face=Arial></FONT> </DIV></DIV>
<DIV>
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style="FONT-STYLE: normal; DISPLAY: inline; FONT-FAMILY: 'Calibri'; COLOR: #000000; FONT-SIZE: small; FONT-WEIGHT: normal; TEXT-DECORATION: none"><FONT
size=2 face=Arial>The next generation of brightness enhancement schemes uses
materials with differing absorption and emission spectra to play additional
“tricks”. New engineered optical materials, called photonic band gap
materials, could play a key role here.</FONT></DIV></DIV>
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<DIV
style="FONT-STYLE: normal; DISPLAY: inline; FONT-FAMILY: 'Calibri'; COLOR: #000000; FONT-SIZE: small; FONT-WEIGHT: normal; TEXT-DECORATION: none"><FONT
size=2 face=Arial></FONT> </DIV></DIV>
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size=2 face=Arial>If these solar brightness-enhancement schemes pay off, they
will be able to fund all of high energy
physics....</FONT></DIV></DIV></DIV></DIV></BODY></HTML>