Investigating the Electron Cyclotron Maser Instability in Laser-Ionized Plasmas

We propose using circularly polarized lasers to ionize plasmas to study the electron cyclotron maser (ECM) in the lab. The ECM instability needs specific momentum distribution functions (MDFs) with inverted Landau populations to develop. These MDFs have gained attention recently due to advancements in understanding how these inverted populations can be naturally generated near extreme astrophysical objects [Bilbao et al., PRL 2023]. Hence, finding ways to study this instability in the lab is timely.

During plasma ionization, lasers can transfer their polarization to the MDF [Zhang et al., Sci. Adv. 2019]; therefore, circularly polarized lasers can generate plasmas with long-lasting ring-shaped MDFs in an external magnetic field. These distributions are similar to those predicted due to synchrotron cooling near highly magnetized astrophysical objects, like pulsars. Thus, as we will discuss in this work, a simple setup of laser-target interaction in an external magnetic field can be used to explore and understand this instability and its features. We use theory and particle-in-cell simulations to identify the plasma and laser characteristics needed to study the ECM instability with current technology, focusing on generating relativistic ring MDFs and understanding the instability's growth and signatures for future lab experiments.