Low-temporal coherence light self-focusing effect by spatial resolved method

Abstract

The low-temporal coherence light (LTCL) has received extensive attention in the research of inertial confinement fusion due to its physical properties of instantaneous broadband. Recent reports demonstrated that the LTCL has significant suppression effects on laser plasma instability. However, the temporal spike structures of the LTCL will not only induce the amplification of the self-focusing effect, but also make its small-scale self-focusing characteristics and corresponding damage mechanism more complicated. Exploring the self-focusing characteristics of the LTCL will provide an important information for improving the output power of the LTCL. In this work, we design a more accurate test method for comparing the nonlinear self-focusing effects of different lasers, and compare the self-focusing effect of LTCL with single longitudinal mode (SLM) pulse. In the experiments, fused silica is tightly focused by a short focal length lens to avoid damaging the input surface. A spatially resolved test method is designed to measure the nonlinear <i>I</i>×<i>L</i> value (where <i>I</i> is the incident intensity, <i>L</i> is the distance from the head of filamentation damage to the input surface), which is accumulated from the input surface to the head of filamentation damage. The results show that the nonlinear <i>I</i>×<i>L</i> value obtained by the spatially resolved method is lower than by the traditional test method, since the energy loss caused by incident surface damage and backward stimulated Brillouin scattering (SBS) has been resolved. Furthermore, the nonlinear <i>I</i>×<i>L</i> values of the SLM pulse and the LTCL are also compared by the traditional test method and spatially resolved method. The test results show that due to the temporal spike structure, the LTCL has a lower nonlinear <i>I</i>×<i>L</i> value than the SLM pulse. The SBS effect and the different damage characteristics of the input surface are also analyzed. This study provides a more accurate test method for better analyzing the self-focusing effect of LTCL and laser pulses with different characteristics, and hence presenting a reference for designing high-power devices of low-temporal coherence light.