Recently, the team from the Joint Laboratory on High-Power Laser Physics at the Shanghai Institute of Optics and Fine Mechanics (SIOM), Chinese Academy of Sciences, has achieved new progress in the research of precision computational optical field measurement for high-power lasers. By combining physical optical imaging with computational optical imaging technologies, the research team significantly enhanced the measurement accuracy of computational optical fields for high-power lasers. The related findings were published in High Power Laser Science and Engineering under the title "Computational near-field and far-field parameter measurement of high-power lasers using modified coherent modulation imaging."
Computational optical field measurement for high-power lasers enables the simultaneous measurement of the laser's complex amplitude (intensity and wavefront/phase). It can also reconstruct the high dynamic range focal spot distributions at different planes in the far field. This capability provides crucial technical support for the precise analysis of physical target conditions and the stable operation of high-power laser facilities. However, existing research faces a challenge: under single-exposure data acquisition conditions, computational wavefront-coded imaging suffers from insufficient signal-to-noise ratio (SNR) when reconstructing the complex amplitude of large-aperture laser beams. This limitation makes it difficult for the measurement accuracy to meet the practical requirements of laser parameter measurement in actual laser facilities.
To address this issue, the research team, based on the measurement optical path parameters of existing setups, integrated direct-imaging data of sampled large-aperture laser beams into the computational wavefront-coded imaging process. They further employed improved algorithms to effectively enhance the SNR for reconstructing the complex amplitude of large-aperture laser beams. During experiments, the team calibrated the static aberrations of the computational optical field measurement system and successfully measured the complex amplitude optical fields of high-power pulsed lasers with large energies. The experimental results demonstrate that this method surpasses Hartmann wavefront sensing in near-field wavefront resolution. Furthermore, the dynamic range presented in the measured far-field focal spots (176 dB) is significantly higher than that achieved by traditional direct imaging techniques (62 dB). This method offers advantages including a simple structure, high measurement accuracy, and good environmental adaptability. It holds promise for applications in frontier scientific research (such as high-energy-density physics), industrial inspection and intelligent manufacturing, and biomedical and life sciences.
Figure 1. (a) MCMI measurement package in the Shenguang-II laser device. (b) Location of components in the MCMI measurement package.
Figure 2 Comparison measurement results for a high-power laser of energy 3272 J and pulse width 3 ns. (a) Near-field intensity calculated using MCMI. (b) Near-field phase calculated using MCMI. (c) Far-field focal spot calculated using the MCMI method. (d) Encircled energy corresponding to the focal spot shown in (c). (e) Near-field intensity directly measured and captured by CCD4. (f) Near-field phase directly recorded by a Shack–Hartmann wavefront sensor. (g) Far-field intensity directly captured by CCD3. (h) Encircled energy corresponding to the focal spot shown in (g).
Figure 3 Computational evolution of the focal spot in proximity to the focal plane. These images were obtained through the computational propagation of the reconstructed complex amplitude along the optical axis. These images share the same scale bar.
This research received support from the National Major Science and Technology Projects, the National Natural Science Foundation of China, the Ministry of Industry and Information Technology, the Chinese Academy of Sciences, the Shanghai Municipal Science and Technology Commission, and other projects.
