From the Archive
A method of cutting off three-inch pieces from a beam of light,
like a meat cutter slicing a bologna sausage, though the light
moves at 186,000 miles a second, is described by Dr. Ernest O.
Lawrence and Dr. J. W. Beams of
Yale University.
Though light travels so fast that
it can encircle the earth seven
times in a second, the two physicists made use of a shutter that
turned the light on and off with
such rapidity that each “piece” of
light was only about three inches
in length. Each flash lasted a hundred billionth of a second.
The investigation was under-taken in an endeavor to measure the length of what are called
“quanta” of light, for according to
modern ideas, light is transmitted
as separate pulses, each of which is
called a quantum. Physicists have
been uncertain as to how long
these quanta are, but by some it
was believed that they were as
much as a yard in length.
These extremely short flashes
of light were measured by a very
delicate photoelectric cell, which
gives off an electric current when
illuminated, and they found that
so long as the total amount of light
reaching the cell was the same,
the resulting current was not
affected by the length of the individual flashes. One three inches
long produced an effect as well as
a piece of light many miles or more
in length, and this shows, say the
investigators, that the individual
quanta are less than three inches
in length.
Femtosecond lasers (this one at Imperial College London) emit pulses lasting quadrillionths of a second.
UPDATE
Photon size a trickier question today
To vote for one of these topics to
appear on From the Archive, visit
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A. What protons had to say about
matter’s next smallest level
B. Computing in tandem with Illiac IV
C. The rest of the Chindesaurus story
