Edible lasers: What's the next course?

LIGHT | TOUCH
Edible Lasers:
What’s the Next Course?
Stephen R. Wilk
Thirty-five years have passed since Ted Hänsch and Art Schawlow invented
the world’s first edible laser. Is there hope for a future in culinary photonics?
Steve Wilk savors the possibilities.
When I was in graduate school in
the 1980s, stories had been circulating
about how someone had actually
constructed a laser using Jell-O. And,
sure enough, when I looked through
the Science Citation Index and Physics
Abstracts Index, I located “Laser Action
of Dyes in Gelatin,” by T.W. Hänsch,
M. Pernier and A.L. Schawlow in the
January 1971 IEEE Journal of Quantum
Electronics. The paper revealed that the
lasing material wasn’t the colorful Jell-O
that we associate with dessert, but rather
a clear, unflavored gelatin that had been
mixed with sodium fluorescein dye.
I was grateful when Theodor Hänsch
wrote an OPN article titled “Edible
Lasers and Other Delights of the 1970s”
in February 2005 to tell the story of their
edible laser. Apparently, Arthur Schawlow
really had tried to make colored, flavored
gelatin lase. Unfortunately, none of the
12 flavors he had bought would act as
a laser. (However, Hänsch noted that
Schawlow “took the obstinate experiment
to his office and savored it as a snack.”)
Arthur Schawlow really
had tried to make
colored, flavored gelatin
lase. Unfortunately,
none of the 12 flavors
he had bought would
act as a laser.
Not one to give up, Schawlow pointed
out that sodium fluorescein dye was
“almost non-toxic,” so the researchers
mixed it into the gelatin.
This got me wondering about whether
there are any other edible lasers. It’s
been more than 35 years since Hänsch
and his colleagues published their letter;
perhaps the time has come to develop
another laser snack. Let’s consider some
possibilities.
For the purposes of this exercise, I
will assume that only the lasing medium
needs be edible. I’ll also allow that the
medium might not be easy to consume
in the condition that it must be in
for lasing: It might have to be cooled,
heated, ground-up, or otherwise subjected
to a temperature or size change—
but it won’t undergo significant chemical
changes or be placed in mixtures or
solutions. I think that’s fair.
Dyed lasers
That doesn’t leave much to work with.
Most solid-state lasers are out, since you
can’t digest glass or crystal hosts. Gas
lasers are disqualified too, since noble
gases freeze out at temperatures well
below that of liquid nitrogen; neon isn’t
much better; and metal vapors condense
to, well, metals. The cadmium out of a
HeCd laser isn’t edible. So what remains?
A search through reference books,
databases and patent literature didn’t
turn up much. One place to start is with
14 | OPN May 2009
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laser dyes. As Schawlow noted, sodium
fluorescein isn’t very toxic. Neither, for
that matter, are coumarin dyes. One
expert I spoke with noted that some
dyes, such as the sulforhodamines, exit
the body quickly and would arguably be
a better choice if you were determined
to drink your dye. (I want to emphasize
that I am NOT advocating this. I
strongly insist that you do not try this
at home.)
All of these dyes are soluble and
lasable in ethanol, so you could, in principle,
drink them. In fact, a droplet of
alcohol containing the dye would itself
constitute a complete laser, as Hänsch
showed. With the light totally internally
reflecting from the interior droplet
surfaces, the entire laser is edible. The
actual toxicity of these dyes has not been
fully established, however. Certainly
most laser dyes are toxic, especially the
cyanide-based ones. Also, these examples
of laser dyes in gelatin or ethanol
don’t stray far from the work of Hänsch
and Schawlow.
Salty lasers
One new possibility is a color-center
laser, which uses point defects in crystal
lattices as broadband, tunable laser sources.
Granted, many of these crystals are
minimally soluble, indigestible crystals
such as lithium fluoride or even diamond.
But most of the lasing defects are in
potassium chloride or sodium chloride.
Two of the crystals used by the only
commercial color center laser were
potassium chloride, which is certainly
edible when ground up or licked; in
fact, it’s used as a salt substitute. Most
of the color centers involve impurities
introduced into the crystals, but these
are at low concentrations—typically
about 1 percent—and most are benign,
being other alkali metal ions. However,
both KCl and NaCl crystals are host to
defects that don’t involve impurities.
Besides defect lasers, there are also
laser materials in which the salt crystal
acts as a host medium for lasing molecular
ions. My own work on superoxide
ions in salt crystals is an example.
“One-Drop-Only” dye laser, a precursor of
the edible laser.
One new possibility is
a color-center laser,
which uses point
defects in crystal
lattices as broad-band,
tunable laser sources.
Unfortunately, there aren’t too many
other edible crystals. However, there are
alkali halide crystals, and other color
centers in some of those (such as rubidium
chloride or potassium bromide).
No one, to my knowledge, has reported
laser properties in defects or impurity
centers in, say, rock candy, or crystallized
proteins. Perhaps this column will spur
someone to take up the challenge.
Liquid lasers
What about liquids? Our choices here
are limited as well. Water and ethanol
are potable, but most other fluids,
including organic liquids, are not. You
can drink small amounts of glycerine,
but I haven’t been able to lase them,
even with the inclusion of dyes. Aside
from organic compounds and their
perhalogenated analogs, and silicones,
most substances that are liquid at room
temperature are either highly toxic or
highly reactive in the presence of organic
liquids and water.
However, water and alcohol in vapor
form meet my guidelines: Although you
can’t consume them as a vapor, you can
condense and drink them without making
any other alteration. There are about
two dozen lines on which water vapor
will lase continuously between 2 and
350 µm. And ethyl alcohol has been
found to lase at 396 µm. There must be
others. Methyl alcohol has more than
100 lasing lines in the infrared. Perhaps
this is a fruitful area for future research.
And what about the fabled gin-and
tonic laser, another rumor I’d heard during
my graduate school days? According
to D.A. Jennings, K.M. Evenson and
J.J. Jimenez, all working at the NIST
laboratory in Boulder, Colo., U.S.A.,
in 1975, the “…ethyl alcohol line lased
very well on vodka, gin and rum, but it
lased on only one line and rather weakly
compared with methyl alcohol. It is quite
obvious that there are better uses of ethyl
alcohol.” I’ll drink to that. t
Stephen Wilk (swilk@comcast.net) is an optical
engineer based in Saugus, Mass., U.S.A.
[ References and Resources ]
>> W.S. Benedict et al. “The water vapor
laser,” IEEE J. Quantum Electron. 5(2),
108-24 (1969).
>> T.W. Hänsch et al. “Laser action of dyes
in gelatin,” IEEE J. Quantum Electron. 7,
45-6 (Jan. 1971).
>> J.G. Kepros et al. “Experimental evidence
of an X-ray laser,” Proc. Natl. Acad. Sci.
USA, 69(7), 1744-5 (1972).
>> D.A. Jennings et al. “New CO 2
pumped
CW far-infrared laser lines,” IEEE J.
Quantum Electron. 11, 637 (1975).
>> A. Kues and G.A. Lutty. “Dyes can be
deadly,” Laser Focus 11(5), 59–61 (May
1975).
>> S.R. Wilk et al. “Laser characteristics
of KNL:O 2
,” Opt. Comm. 47(6), 404-6
(1983).
>> J.F. Pinto et al. “Stable color-center
laser in K-doped NaCl tunable from 1.42
to 1.76 µm,” Opt. Letters 10(8), 384-6
(1985).
>> T.W. Hansch et al. “Edible lasers and
other delights of the 1970s,” Opt. Photon.
News 16(2), 14-6 (2005).
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