Multi-grid parallel ptychographic algorithm for frequency-resolved optical gating

The ptychographic reconstruction algorithm is a commonly utilized method for pulse phase retrieval due to its super-resolution and robustness, allowing it to retrieve pulses from incomplete traces. However, the algorithm's performance can be hindered by occasional convergence stagnation caused by local minima in the gradient descent strategy. To address this issue, we propose a pulse reconstruction approach for frequency-resolved optical gating (FROG), which employs a multi-grid flexible sampling and parallel extended ptychographic iterative engine (ePIE), ultimately converging to the global FROG trace. The approach can effectively escape from the local minima and demonstrates extremely stable convergence without any prior information. We demonstrate, numerically and experimentally, that this approach can converge well to the correct pulse, especially for complex pulse reconstruction, even in cases of high noise and highly incomplete traces.