Speaker
Description
We are developing an open-source numerical computational suite (https://github.com/HHG-modelling/MMA-HHG-pre-release-2) for modelling high-harmonic generation (HHG) in gaseous media. This process provides a tuneable source of highly coherent XUV radiation, forming attosecond pulses that allow the probing of atomic and molecular processes (such as chemical reactions) at their natural temporal scales. Our goal is to establish an open-source community codebase that will become standard in the field, unify various approaches, and provide interfaces and data standards. The initial release, which is now under finalisation, describes the multiscale problem of HHG in the gas phase in its full complexity: the macroscopic scale for field description and the microscopic scale for laser–matter interaction. The development is motivated and accompanied by laboratory applications.
The nature of the problem allows us to pipeline the subtasks: (a) the propagation of the driving laser (unidirectional pulse propagation), (b) the time-dependent Schrödinger equation (TDSE) for the microscopic response, and (c) the diffraction-integral approach to aggregate the macroscopic XUV field from the microscopic emitters. Because the numerical computations are expensive, all modules use MPI or multithreading parallelisation. The main computational routines are written in low-level C/Fortran, complemented by Pythonic high-level routines for pre- and post-processing. The computational interface is the HDF5 data structure, which reduces data handling for visualisation and post-processing. For example, the phase and intensity profiles of the incident laser might be masked by phenomenological semi-classical models approximating the most probable quantum trajectories, providing an estimate of the XUV signal. Complementary to the main pipeline, all the modules are available as stand-alone applications. Namely, the pulse propagation can be used to study, for example, laser filamentation; the TDSE is available as a dynamic library for Python; and the computation of the XUV diffraction integral comes with its own interface. The recent developments allow multiplatform deployability (Intel/GNU/AppleClang) on various supercomputers, now moving towards IT4I as one of the main computational resources for the developers’ team. Pythonic interfaces make the computational routines easy to use and present the data in an understandable form. The code is accompanied by Jupyter tutorials to make it more user-friendly.
The initial deployment of the code was tested during Project FTA-25-17. The official release, accompanied by a publication, is under preparation. Moreover, the model already provides fertile ground for various applications. For example, completed work includes optimisation of the HHG source in a pre-ionised gas (https://doi.org/10.1038/s41598-022-11313-6), and ongoing work concerns a monochromatising scheme investigated in Project OPEN-34-87 related to GAČR 25-17853S.
The contribution will provide a general overview of the code suite and then present various selected applications.
