Reconstructing multi-spectral wavefronts from measured speckle patterns

The highest possible spatio-temporal quality of a focused ultrashort laser pulses is a key factor in experiments relying on highest peak intensity and/or shortest duration. Such pulses, are naturally broadband and thus can have different wavefronts for different frequencies. Accurate measurements of the spectrally-resolved phase front have been challenging to implement.

Lead by Slava Smartsev of LOA’s APPLI group and Aaron Liberman of the Weizmann Institute of Science, Israel, a novel and technically straightforward approach has been developed for the measurement of the spectrally resolved wavefront of an ultrashort laser pulse.

The minimally intrusive method new method, called IMPALA (Iterative Multispectral Phase Analysis for LAsers) relies on placing a mask with specially arranged pinholes in the beam path before the focusing optic, imaging the speckle pattern produced at focus, and retrieving from it the spectrally resolved laser wavefront through an iterative algorithm.

In a first experimental demonstration on the 30-fs Ti:sapphire laser system in Salle Noire 3 at LOA, chromatic aberrations, such as pulse-front tilt (PFT), pulse-front curvature (PFC), and higher-order aberrations introduced by a spherical lens have been accurately retrieved.

The simplicity and scalability of this method, combined with its compatibility with single-shot operation, make it a strong complement to existing tools for high-intensity laser facilities.