Scaling of femtosecond supercontinuum generation above the ablation threshold in fused silica

The extremely short pulse durations and high peak powers achievable with sub-picosecond ultrashort pulse laser (USPL) systems have enabled the utilization of a nearly endless list of non-linear optical processes. One of these processes is broadband supercontinuum (SC) generation, which is predominantly due to the Kerr effect.For laser intensities near the material ablation threshold, SC generation becomes complicated by the high-density electron plasma that forms. This work presents results and analysis concerned with single-shot broadband supercontinuum generation (SCG) in a 1 mm thick fused silica window with 40 fs pulses as the incident pulse fluence increases through the ablation threshold. For incident pulse energies below the ablation threshold, the beam profile of the emitted SC light exhibits a conical emission structure similar to observations made by other groups. However, the beam is significantly less structured for energies above threshold, and theenergy scaling of spectral regions outside of the fundamental spectrum suggests that the electron plasma plays a significant role in this regime. We speculate that complex scattering and absorption from electron plasma hot spots at multiple filamentation collapse locations within the window strongly affect the emitted SC light.