New technique measures ultrashort laser pulse... (pecialized fibers called near-field scan...)

New technique measures ultrashort laser pulses at focus

Date:5/9/2008

pecialized fibers, called near-field scanning optical microscopy fibers, which can resolve features smaller than the wavelength of the light.

The researchers tested the device by measuring ultrashort pulses focused by various lenses, since each lens can cause different complex distortions. To validate the measurements, Bowlan performed simulations of pulses propagating through the experimental lenses. Results showed that a common plano-convex lens displayed chromatic and spherical aberrations, whereas more expensive aspheric and doublet lenses exhibited mostly chromatic aberrations.

Spherical aberrations occur when the light that strikes the edges of the lens gets focused to a different point than the light that strikes the center, creating a larger, inhomogeneous focused spot size. Chromatic aberrations occur because the many colors in the laser travel at different speeds and do not stay together in space and time as the pulse passes through glass components in the experimental setup, such as lenses. As a result, each color arrives at the focus at a different time, creating a rainbow of colors in the electric field images.

Aberrations can drastically increase the pulse length, which decreases the laser intensity. A lower intensity forces researchers to increase the power of the laser, increasing the possibility of damaging the sample. Aberrations can also yield odd pulse and beam shapes at the focus, which complicate the interpretation of the experiment or application.

Our system tells researchers what types of aberrations are present in instrumentation, which then allows them to test different lenses in the instrumentation setup or use a pulse shaper to create the desired pulse at the focus thats free of distortions, added Bowlan.

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Contact: Abby Vogel
avogel@gatech.edu
404-385-3364
Georgia Institute of Technology Research News
Source:Eurekalert

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New technique measures ultrashort laser pulse...(pecialized fibers called near-field scan...)