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Departmental Colloquium

Measuring Everything You’ve Always Wanted to Know About an Ultrashort Laser Pulse, But Were Afraid to Ask  
Guest Speaker
Rick Trebino  
Thursday, February 11, 2010 4:00 pm - 5:00 pm  
202 Physics  

Dr. Susanne Ullrich will host Dr. Rick Trebino of the Georgia Institute of Technology Department of Physics this week. His talk is is entitled "Measuring Everything You’ve Always Wanted to Know About an Ultrashort Laser Pulse, But Were Afraid to Ask."

Measuring an event in time seems to require a shorter one. As a result, the development of a technique to measure ultrashort laser pulses—the shortest events ever created—has been particularly difficult. We have, however, developed simple methods for fully characterizing these events, that is, for measuring a pulse's intensity and phase vs. time. One involves making an optical analog of a musical score of the pulse by using nonlinear optics to measure the pulse spectrogram. The mathematics involved is equivalent to the two-dimensional phase-retrieval problem—a problem that’s solvable because the Fundamental Theorem of Algebra fails for polynomials of two variables. We call this method Frequency-Resolved Optical Gating (FROG), and it’s simple, rigorous, intuitive, and general. FROG has been used to measure pulses as short as 100 attoseconds (10-16 sec) and as weak as a few hundred photons. FROG has also measured the most complex ultrashort pulse ever generated, yielding surprising results. And we have recently developed methods (also with frivolous names: SEA TADPOLE and STRIPED FISH) for measuring the complete spatio-temporal field of an arbitrary laser pulse, making ultrashort laser pulses the most completely characterized form of light known to humankind.