Optical-field ionized plasma: A laboratory platform for kinetic plasma effects, laboratory astrophysics and beyond

Chen-Kang Huang^1,2*

¹Department of Physics, National Central University, Taoyuan, Taiwan
²Center for High Energy and High Field Physics, National Central University, Taoyuan, Taiwan

* Presenter:Chen-Kang Huang, email:ckhuang@cc.ncu.edu.tw

Optical-field-ionized (OFI) plasmas, created when intense laser pulses fully ionize a gas via strong-field ionization (tunneling or multiphoton ionization), have long served as a foundational tool in atomic and plasma physics. Historically, these plasmas were regarded as spatially homogeneous and relatively cold, and their dynamics were considered less intriguing than those found in highly nonlinear, extreme-intensity regimes. This talk reviews recent progress in the generation, diagnosis, and theoretical modeling of OFI plasmas, emphasizing their emerging role as a controllable and versatile platform that not only provides a background medium but also serves as a frontier for exploring novel plasma phenomena. OFI electrons are born directly from the laser field on femtosecond timescales, enabling control over their initial conditions through the laser’s frequency, polarization, temporal and phase-front structures, and the choice of gas species. These plasmas are inherently out of equilibrium and exhibit pronounced kinetic features, including non-Maxwellian electron distributions, self-generated magnetic fields, and transient coherent density structures. The ability to precisely initialize and rapidly probe OFI plasmas allows direct investigation of the growth and saturation of kinetic instabilities from well-defined initial states. We further highlight the impact of this platform on laboratory astrophysics, particularly for studying magnetic field generation via the thermal Weibel instability, a process critical to understanding the origin of galactic magnetic fields. Moreover, we demonstrate that electron motion during ionization renders the plasma inherently nonuniform. When driven by a laser field carrying angular momentum, the plasma is imprinted with a spiral density structure, qualitatively reminiscent of galactic spirals yet distinct in its origin. This density modulation reflects angular momentum transfer from the laser field to the plasma and subsequently evolves into fine filamentary structures driven by intrinsic kinetic instabilities.

Keywords: Laser-plasma interaction, Optical-field ionization, Plasma instabilities, Plasma kinetic effects, Laboratory astrophysics