Enhanced nanosecond-scale pulse contrast measurement for petawatt-class lasers based on laser filamentation

• We propose a nanosecond-scale pulse contrast measurement method based on laser filamentation in water, which can not only protect photodiodes from high-energy lasers but also enable precise detection of tiny noise. After seven thousand laser shots, the sensitivity of the photodiodes retained 60 % of its initial value. • Pulse contrast measurement performed on SG-II confirm the practical viability of the proposed method. The preceding parametric fluorescence was observed, and the measured pulse contrast exhibited significant variation under different optical path configurations. Independent validation using a third-order cross-correlator (Sequoia 1000 of Amplitude Inc.) demonstrates good consistency with these results. • This method has the advantages of high reliability and repeatability. Its robust performance and consistent measurement capability make it well suited for the nanosecond-scale pulse contrast diagnostic in petawatt-class laser systems. Pulse contrast is a crucial parameter for evaluating the performance of petawatt laser systems. On the nanosecond timescale, pre-pulse-induced plasma expansion can significantly influence the interaction between the main pulse and the target, potentially degrading experimental outcomes. To enhance the reliability of pulse contrast measurement, we propose a novel method based on laser filamentation in water, which effectively protects the photodiodes while maintaining high measurement fidelity. Experimental results demonstrate that this method enables a main pulse attenuation factor of up to 40, while pre-pulses with relative intensity below 10 –5 are not attenuated. After seven thousand laser shots, the photodiode retains approximately 60 % of the initial sensitivity. Furthermore, a Michelson-type optical platform was developed to enable high-precision pulse contrast calibration. Based on the measurement and calibration platforms, pulse contrast was measured on SG-II. The results reveal significant variations in pulse contrast under different optical path configurations, in agreement with theoretical predictions. In addition, independent validation using a commercial cross-correlator confirms the reliability of the results. The setup achieves a dynamic range of 10 9 at 2 mJ, potentially extending to 10 10 at 20 mJ, providing a robust solution for nanosecond-scale contrast diagnostics in high-energy laser systems.