Ultra-high intense laser pulses have been applied in the field of laser-matter interaction, such as proton or electron acceleration in thin solid targets and electron generation in fast-ignition inertial confinement fusion. State-of-the-art high-power laser systems can produce intense pulses with peak powers of 10 PW. The 100-PW level laser system with focal intensities of 10²¹–10²⁴ W/cm² is expected in the near future. For the PW laser pulse, the temporal contrast is one of the most important parameters since the prepulse noise has disturbing influence to the laser-matter interaction. Thus the temporal contrast measurement for the ultra-intense laser pulse is critical.

For all techniques to improve the temporal contrast of ultra-intense laser pulses, limited methods were developed for the temporal contrast of single-shot measurement. So far, typical method is still the third-order auto-correlator (TOAC). In the TOAC, ghost prepulses will be introduced by the strong postpulses of the sampling pulse. Furthermore, the group velocity mismatch (GVM) between the sampling pulse and the test pulse will influence the time resolution.

Recently, a research team from Shanghai Institute of Optics and Fine Mechanics of Chinese Academy of Sciences, proposed a novel and simple method single-shot fourth-order auto-correlator (FOAC). The results were published in Advanced Photonics.

In this new method, the sampling pulse with high energy was generated by a frequency-degenerate third-order nonlinear processes and the correlation signal was achieved by a sum-frequency generation process with large crossing angle and then captured by using a 16-bit sCMOS. The clean sampling pulse owning to the third order process guaranteed a high measurement fidelity. The identical central frequency between the sampling pulse and test pulse eliminated the influence of the GVM.

As a result, high time resolution was obtained together with a sCMOS as the detector. The proof-of-principle experiments showed that a dynamic range of approximately 10¹¹ compared with the noise level, a time resolution of approximately 160 fs, and a time window of 65 ps could be successfully obtained.

Furthermore, the temporal contrast of laser pulse from a PW laser system was successfully measured in single-shot with a dynamic range of about 2×10¹⁰ and simultaneous a time resolution of 160 fs.

The novel single shot FOAC would contribute to the optimizing the PW laser system and analyzing the ultra-high intense laser-matter interaction research activities. In the future, researchers aim to obtain higher dynamic ranges by increasing the correlation signal energy and sensitivity of the detector, and combining the temporal contrast reduction techniques.

The work was supported by National Natural Science Foundation of China; the Instrument Developing Project and the Strategic Priority Research Program of the Chinese Academy of Sciences; Shanghai Municipal Science and Technology Major Project.

(a).Schematic representation of the proof-of-principle experimental setup (b).The comparison of the TOAC and FOAC measurement results.

Article website:
http://www.clp.ac.cn/EN/Article/OJ314352fde5d65eb3

Contact:
Mr. CAO Yong
General Administrative Office
Shanghai Institute of Optics and Fine Mechanics, CAS
Email: caoyong@siom.ac.cn