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DESCRIPTION:Rick Trebino\, Georgia Tech\n\nTo measure an event in time requ
ires a shorter one. As a result\, the\ndevelopment of a technique to measu
re ultrashort laser pulses--less than\n\n10-12 seconds long and
the shortest events ever created--has been\nparticularly difficult. We ha
ve\, however\, recently developed a simple\nmethod for fully characterizin
g these events\, that is\, for measuring a\npulse's intensity and phase vs
. time. This method relies on two seemingly\nunrelated ideas: the concept
of the musical score and the fact that the\nFundamental Theorem of Algebra
fails in two dimensions. Specifically\, an\noptical analog of a musical s
core of the pulse is produced by measuring its\nspectrogram. And the mathe
matics involved is equivalent to the\ntwo-dimensional phase-retrieval prob
lem--a problem that is solvable only\nbecause the Fundamental Theorem of A
lgebra fails in two dimensions. We call\nthe method Frequency-Resolved Opt
ical Gating (FROG)\, and it is simple\,\nrigorous\, intuitive\, and genera
l. It can measure pulses in all spectral\nranges\, on a single-shot basis\
, and over a wide range of energies. FROG has\nbeen used to measure pulses
as short as 4.5 femtoseconds (4.5 x 10-15 sec)\,\nand it can m
easure two pulses simultaneously. More recently\, we have shown\nthat FROG
can be used in conjunction with spectral interferometry to measure\nessen
tially arbitrary pulses with as little as zeptojoules of energy (less\ntha
n one photon!) on a multi-shot basis.\n
DTSTART:20001110T210000Z
LOCATION:Physics Building\, Room 204
SUMMARY:The Musical Score\, the Fundamental Theorem of Algebra\, and the Me
asurement
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