Laser-driven inertial confinement fusion (ICF) diagnostics serve as a pivotal methodology for elucidating the intricate physical processes underlying ICF and achieving thermonuclear ignition. During ICF experiments, the interaction between high-power lasers and the ablator layer of a target capsule generates a plasma critical surface, which reflects a substantial fraction of the incident laser energy, thereby impeding efficient energy transfer to the fuel core. This reflection-induced energy loss significantly diminishes the conversion efficiency of laser energy into implosive kinetic energy. Consequently, effective diagnostic characterization of the plasma critical surface is critical for optimizing ICF performance ^[1-6]. However, the extreme transient nature of the critical surface—characterized by ultrashort temporal scales (sub-nanosecond) and microscopic spatial dimensions (micrometer-scale)—poses formidable challenges for existing diagnostic techniques in resolving its morphology and dynamic evolution.
To address this limitation, we propose a novel optical diagnostic approach based on spectrally chirped pulses for probing the spatiotemporal evolution of the plasma critical surface in ICF experiments. This method exploits the laser spectral modulation effects induced by reflection at the critical surface. Through carefully designed experiments, we have successfully demonstrated the efficacy of this technique in capturing both the temporal evolution of the critical surface morphology and its radial expansion velocity.
By providing unprecedented insights into critical surface behavior, this diagnostic framework offers a transformative strategy for optimizing laser irradiation uniformity, enhancing target surface symmetry, and ultimately improving the laser-to-kinetic-energy conversion efficiency. These advancements hold significant potential to advance ICF research toward achieving robust ignition conditions.

ICF diagnose,direct drive,critical surface evolution