Recently, the research team from the Joint Laboratory on High Power Laser Physics at the Shanghai Institute of Optics and Fine Mechanics (SIOM), Chinese Academy of Sciences, addressed the challenges of detector damage and limited dynamic range in nanosecond-scale pulse contrast measurement for high-power laser facilities. They proposed and demonstrated a novel measurement method based on laser filamentation, providing a new technical solution for related diagnostics. The findings were published in Optics and Lasers in Engineering under the title "Enhanced nanosecond-scale pulse contrast measurement for petawatt-class lasers based on laser filamentation."

Pulse temporal contrast is a crucial parameter for evaluating the performance of petawatt-class laser systems, as noise within the nanosecond window can also adversely affect high-energy laser experiments. However, traditional measurement methods based on photodiodes are susceptible to damage from the main pulse, limiting measurement accuracy and dynamic range, thus calling for more reliable techniques.

To address these issues, the team innovatively proposed and experimentally validated a nanosecond-scale pulse contrast measurement method based on laser filamentation in water. This technique utilizes nonlinear optical attenuation generated by the laser-matter interaction to effectively protect the photodiode, achieving up to 40-fold attenuation of the main pulse without affecting low-intensity prepulses. The system demonstrated excellent long-term stability, with the photodiode maintaining high sensitivity even after multiple laser exposures. Furthermore, the team established a high-precision contrast measurement and calibration platform with a temporal window extending to -10 ns.

Using this setup, the team conducted pulse contrast measurements on the Shenguang II picosecond petawatt laser system, achieving a dynamic range of 10^9. The study revealed significant differences in pulse contrast under different optical configurations, with the results showing strong agreement with theoretical predictions and measurements from a commercial third-order cross-correlator. Increasing the incident energy is expected to further extend the dynamic range to 10^10, providing robust technical support for high-contrast pulse diagnostics in high-power laser facilities.

This work was supported by the Chinese Academy of Sciences Strategic Priority Research Program and the National Natural Science Foundation of China.

Fig.1 Diagram of the nanosecond-scale pulse contrast measurement based on the nonlinear optical attenuation effect

Fig. 2 Pulse contrast measurement results in the SG-II picosecond PW laser system: (a) nanosecond-scale pulse contrast measurement (b) sub-nanosecond-scale pulse contrast measurement using third-order scanning cross-correlator.