Method of statistically characterizing target plane light field properties in inertial confinement fusion device
Authors: Yang Jun-Lan , Zhong Zhe-Qiang , Weng Xiao-Feng , Zhang Bin ,   College of Electronics and Information Engineering, Sichuan University, Chengdu 610064, China
Published: December 2020

In the laser-driven inertial confinement fusion facilities, the irradiation uniformity of the laser beams on the target is a key factor affecting the effective compression of the target. At present, a variety of beam-smoothing techniques have been developed to control the spatiotemporal characteristics of the focal spots. However, many optical components involved in optical transmission links and complex transmission transformations often lead to complex optical transmission. Moreover, when using the diffraction optical method to analyze the shape and characteristics of the focal spots, a lot of data are needed to be processed and calculated, resulting in large calculation and low computational efficiency. It is urgent to find a new and fast method to describe the statistical properties of the focal spots. In addition, in the beam-smoothing technique, since the phase distribution of the continuous phase plate is obtained by multiple iterations of random numbers, although the details of focal spots obtained by different continuous phase plates are not the same, they all have similar statistical properties. Therefore, the modulation of the laser beam by the continuous phase plate can be regarded as the transmission process of the laser beam through a random surface. Although the intensities of the speckle within the focal spot at different locations have the strong randomness, and the random distributions of the target speckles obtained by different beam-smoothing methods are different, the overall distribution satisfies a certain statistical law. In this paper, the light-field properties of the focal spot are described by the statistical characterization method. The circular complex Gaussian random variables are used to directly describe the statistical properties of the target surface light field, and the far-field focal spots obtained by the diffractive optical method and those by the statistical characterization method are compared with each other and analyzed based on the typical focal spot evaluation parameters. The results show that the instantaneous properties of the focal spots obtained by the diffractive optical method and those obtained by the statistical characterization method are basically identical, but their time-integrated far-field focal spots are different. The correlation coefficient can be further used to describe the time-varying properties of the far-field focal spots. Compared with the diffractive optical method, in the numerical calculation process, the statistical characterization method of light field properties can directly obtain the analytical expression of the statistical distribution of the light field according to the statistical properties of the continuous phase plate surface shape. Secondly, this method can avoid the numerical calculation process from near field to far field. Last but not least, there is no need to perform data processing on each point of the light field, which makes things simple and effective and does not require large-scale data storage and processing.