Abstract
We demonstrate a method for broadband laser pulse characterization based on a spectrally resolved cross-correlation with a narrowband flat-top gate pulse. Excellent phase-matching by collinear excitation in a microscope focus is exploited by degenerate four-wave mixing in a microscope slide. Direct group delay extraction of an octave spanning spectrum which is generated in a highly nonlinear fiber allows for spectral phase retrieval. The validity of the technique is supported by the comparison with an independent second-harmonic fringe-resolved autocorrelation measurement for an 11 fs laser pulse.
Highlights
Pulsed lasers have become an important tool for nonlinear optical experiments and multiple characterization techniques evolved
Extension to the time-frequency domain was first demonstrated by Treacy in 1971 [3, 4]. Such spectrograms are still used in e.g. frequency-resolved optical gating (FROG) where the electric field is retrieved [5, 6]
XFROG spectrograms are more intuitively analyzed than FROG spectrograms but require a synchronized reference pulse which is well known
Summary
Pulsed lasers have become an important tool for nonlinear optical experiments and multiple characterization techniques evolved. Extension to the time-frequency domain was first demonstrated by Treacy in 1971 [3, 4] Such spectrograms are still used in e.g. frequency-resolved optical gating (FROG) where the electric field is retrieved [5, 6]. Cross-correlation FROG (XFROG) is demonstrated by second-order nonlinear interaction with a well characterized reference pulse [9]. In this paper we present a new method which is compatible to the excitation geometry in typical multiphoton microscopes It is based on degenerate four-wave mixing (FWM) XFROG between an unknown ultrashort laser pulse and a bandwidth-limited narrowband gate pulse with a flat-top profile of the temporal envelope. Enabled by the flat-top shape of the gate pulse, the spectral phase and the intensity can be extracted in a non-iterative manner from the XFROG spectrogram to reconstruct its temporal envelope
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