The 9th International Conference on Matter and Radiation at Extremes (ICMRE2026) ( ICMRE2026)

163 / 2026-03-31 22:42:45

Fiber‑optic diagnostics for studying laser‑coupling and laser–plasma instabilities in fusion plasmas

laser-plasma instability, imaging spectroscopy, laser fusion

Laser and Particle Beam Fusion, Magnetic Driven Fusion > Experiments and Diagnostics

Laser–plasma instability (LPI) processes can significantly degrade laser–target coupling in inertial confinement fusion (ICF) by scattering incident laser energy and generating hot electrons that preheat the fuel. To quantify laser absorption and identify dominant LPI mechanisms, an optical spectrometer system based on 60 channels of fibers has been designed and employed to diagnose light emissions from laser–plasma interactions. The 60 fiber collectors cover an integrated solid angle of π, enabling the measurement of global energy losses in a symmetrical configuration. A detecting spectral range from ultraviolet to near-infrared, with angular distribution, allows for the understanding of the physical mechanisms involving various plasma modes. Experimental measurements of scattered lights from a conical implosion driven by high-energy nanosecond laser beams at the Shenguang-II Upgrade facility have been demonstrated, serving as reliable diagnostics to characterize laser absorption and energy losses from laser–plasma instabilities. This compact diagnostic system can provide comprehensive insights into laser energy coupling in direct-drive inertial confinement fusion research, which are essential for studying the driving asymmetry and improving the implosion efficiencies.

Recent upgrades integrate an intensified CCD (ICCD) with fast time gating to record the temporal evolution of laser absorption. Beyond nanosecond ICF experiments, we have implemented the diagnostic in recent relativistic picosecond laser–plasma interaction experiments, where optical spectra of scattered light (including 2ω₀ and 3ω₀/2 harmonic features) were measured to provide constraints on fast-electron generation and transport.