Strong-Field Steering of Photoelectron Emission Dynamics in Diverse Nanospheres

Understanding the behavior of strong-field photoelectron emission across different nanomaterials is essential for advancing ultrafast laser-matter studies. Here, the emission characteristics of diverse nanospheres, including metals, semiconductors, insulators, organics, and composite materials, are experimentally investigated using intense femtosecond lasers. Within the investigated strong-field range (24–100 TW/cm2), photoelectron emission shows minimal dependence on the nanomaterial type. In this regime, the cutoff energy increases gradually, approaching 10 times ponderomotive energy at 100 TW/cm2. The angular contrast of the emission decreases in magnitude with increasing laser intensity, yet its magnitude rises with increasing ellipticity of the polarization. An intensity-driven transition from backward- to forward-preferred emission is observed, dominated by rescattered electrons. An angular model for nanoplasmonic emission, Y(θ) = a|cos θ| + b, successfully reproduces the reconstructed angular distributions and yields a characteristic plasmon-enhancement parameter. Collectively, these findings establish a nanomaterial-independent strong-field regime in nanoscale targets and provide an empirically constrained angular model to facilitate interpretation and simulation of ultrafast laser-nanoparticle interactions.