Ptychographic reconstruction algorithm for frequency resolved optical gating: super-resolution and supreme robustness

TL;DR

This paper introduces a ptychography-based algorithm for FROG pulse characterization, offering super-resolution, robustness to noise, and the ability to reconstruct from partial spectrograms, surpassing traditional methods.

Contribution

The authors develop a novel ptychographic reconstruction algorithm for FROG that overcomes limitations of existing methods, enabling faster, more robust, and partial spectrogram-based pulse reconstructions.

Findings

Ptychographic FROG reconstruction is faster and more noise-robust than traditional algorithms.

Effective reconstruction from partial and spectrally filtered spectrograms.

Successful blind reconstruction of unknown pulses from limited data.

Abstract

Frequency-resolved optical gating (FROG) is probably the most popular technique for complete characterization of ultrashort laser pulses. In FROG, a reconstruction algorithm retrieves the pulse from a measured spectrogram, yet current FROG reconstruction algorithms require and exhibit several restricting features that weaken FROG performances. For example, the delay step must correspond to the spectral bandwidth measured with large enough SNR a condition that limits the temporal resolution of the reconstructed pulse, obscures measurements of weak broadband pulses, and makes measurement of broadband mid-IR pulses hard and slow because the spectrograms become huge. We develop a new approach for FROG reconstruction, based on ptychography (a scanning coherent diffraction imaging technique), that removes many of the algorithmic restrictions. The ptychographic reconstruction algorithm is significantly faster and more robust to noise than current FROG algorithms, which are based on generalized projections (GP). We demonstrate, numerically and experimentally, that ptychographic reconstruction works well with very partial spectrograms, e. g. spectrograms with reduced number of measured delays and spectrograms that have been substantially spectrally filtered. In addition, we implement the ptychogrpahic approach to blind second harmonic generation (SHG) FROG and demonstrate robust and complete characterization of two unknown pulses from a single measured spectrogram and power spectrum of only one of the pulses. We believe that the ptychograpy-based approach will become the standard reconstruction procedure in FROG and related diagnostics methods, allowing successful reconstructions from so far unreconstructable spectrograms.