Abstract
We present the first technique for directly measuring (without assumptions) the spatio-temporal intensity and phase of a train of ultrashort pulses at and near a focus. Our method uses an experimentally simple and high-spectral resolution variant of spectral interferometry (SEA TADPOLE). To illustrate our technique, we measured the spatio-temporal electric field in and around the foci of several different types of lenses. To confirm our results, we also simulated these measurements by numerically propagating a pulse through each of the lenses used. From one set of measurements, we made a movie showing a focusing pulse with severe chromatic aberration.
Highlights
Almost all applications of ultrashort pulses require focusing them
While scanning SEA TADPOLE bears some resemblance to the method of interferometric photon tunneling scanning microscopy (PTSM) there are some key differences between the two methods [24,25,26,27]
To test scanning SEA TADPOLE, we measured ultrashort pulses focused by various lenses
Summary
Almost all applications of ultrashort pulses require focusing them. Generally, the highest possible intensity is desired, and this is achieved when the pulse is undistorted in both space and time, so that it has a transform limited time duration and a diffraction limited focused spot size. From a typical measurement using our device, a movie can be made of the pulse focusing, showing its intensity and color vs space and time To make these measurements we use a slightly modified version of a device that we recently introduced, called SEA TADPOLE, or Spatial Encoded Arrangement for Temporal Analysis by Dispersing a Pair of Light E-fields [17]. While scanning SEA TADPOLE bears some resemblance to the method of interferometric photon tunneling scanning microscopy (PTSM) there are some key differences between the two methods [24,25,26,27] Both methods involve sampling or spatially resolving the unknown field with an optical fiber (or an NSOM probe in the case of PTSM) and interferometrically recombining it with a reference pulse for each position of the sampling fiber. Interferometric PSTM has primarily been used to measure propagating pulses in photonic structures while scanning SEA TADPOLE is intended for measuring focusing pulses
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