Speaker
Description
The generation of very dense plasmas with ultrafast lasers is key to applications such as tabletop warm dense matter generation—the state of matter found in planetary cores or inertial confinement fusion paths—and laser-induced synthesis of new material phases. For these applications, generating dense plasma inside materials is highly desirable to benefit from large volumes and confined geometries, unlike at solid/vacuum interfaces where plasma expands. A longstanding, challenging issue was that, inside the bulk of transparent materials, the plasma defocuses the intense laser pulse. This drastically limits the peak plasma density well below the critical density.
With ultrafast Bessel beams we have overcome this limitation and demonstrated the creation of subwavelength diameter plasma channels with lengths scalable from tens of micrometers to centimeters. This enables energy density on the order of MJ/cm3, even at modest input pulse energies.
The physical mechanisms underpinning this process have been elucidated through a combination of experimental diagnostics and Particle-In-Cell (PIC) simulations.1 Collisionless resonance absorption dominates energy deposition. The ability of PIC codes to reproduce these results, where hydrodynamic models fail, highlights the importance of capturing the non-Maxwellian electron distributions, such as Landau damping2. Additionally, the extreme confinement of energy deposition explains the efficiency of nano-drilling with Bessel beams, as well as the formation of voids and high-aspect-ratio nanochannels in materials such as sapphire and fused silica.3
These findings open new avenues for both fundamental and applied research. Not only the High-Energy Density regime becomes accessible with tabletop lasers, but nanoplasma rods also enable novel applications in nonlinear optics since the critical surface of the plasma is a surface at epsilon-near-zero, where a number of nonlinear wave conversion can be excited: we have observed second harmonic generation on the nanoplasma rod by the pump pulse itself.4 Our PIC simulations also predict THz emission.5 Ultrafast Bessel beams therefore offer a new, scalable platform for exploring laser-matter interaction in a number of different extreme regimes.
Notes and References
1 K. Ardaneh et al, Physical Review Letters (2026), in print, DOI 10.1103/k23j-c9y7
2 B. Morel, et al, Physical Review B (2022), 106, 035207
3 L. Rapp, et al, Scientific Reports (2016), 6, 34286
4 K. Ardaneh et al, Physics of Plasmas (2022) 29, 072716
5 K. Ardaneh et al, The European Physical Journal Special Topics (2023) 232, 2247–2252