This paper investigates the heat effects of continuous high-power lasers on steel cylinders. A theoretical model combining the mechanical characteristics and heat transfer of the steel cylinder that irradiated by a high-power laser is established. Simulations in temperature fields predict the varying heat effects on steel cylinders corresponding to different laser power levels, and more importantly, the thresholds of laser penetrations. The predictions are further validated by experimental tests, which use 1.5–2.8 kW laser irradiating on 7–15 mm thick steel cylinders. It has been found that the ablation mechanism of steel cylinder is primarily dependent on either the mass transfer of vaporized ablation or liquefied material under the action of vaporized back pressing. The present 0–300 s temperature field analyses show that steel melts at 1720 K and vaporizing ablation happens at 3250 K. It has also been observed that in the contact region between the laser and steel cylinder, the melting and vaporization accompanied by the interaction of the ablation process are followed by the sharp splash phenomenon.

For the paper, experimental studies were performed on the damage of the Ge- and Si-based flat window by lasers out-of-band. The experimental results showed that lasers out-of-band can cause film damage and substrate damage to Ge and Si windows. The high-energy laser damage window mechanism mainly manifested as thermal effects. The composite laser damage thresholds for the substrate were an Si window of 21.6 J/cm² and a Ge window of 3 J/cm². Compared with continuous laser and long pulse laser experimental results, it was found that the use of long pulse-continuous composite constitution could effectively reduce the damage threshold. Compared to the long-pulse laser, the composite laser could achieve similar damage effects with a smaller energy density.

Depicting the multimode laser beam by modal decomposition can potentially assess light field variations in the fiber, during propagation. The practical engineering conditions in the lab however could not realize ideal levels, hence further research on factors influencing this method, such as defocus, is especially necessitated. The grid spacing in observation plane by Fast Fourier Transform is fixed and unchangeable within diffraction imaging, hence possibly yielding erroneous data during obtaining light field intensities. Our research resolves these issues via a Two-step ABCD algorithm, applied in the modal decomposition to characterize various guided modes at the output of multimode fibers. A direct benefit is that the image plane size can be altered, further refining laser facula clarity. Furthermore, the quantitative expressions that analyze defocus factors impacting modal decomposition are acquired. The conclusions thereby prove the modal decomposition algorithm can keep effectiveness in the range of −0.25% to 0.25% of relative defocus for low order eigenmodes, having no suitable limited band for high order eigenmodes, with reference value in engineering applications.

An angular spectrum propagation (ASP) algorithm with a scaling parameter to simulate optical diffraction propagation through optical systems is studied. The alterable observation size is obtained by adding the scaling parameter to the Collins formula. A directly mathematical inverse transformation of the ASP algorithm (IASP) is proposed to calculate the source optical field from the known observation optical field, and the results are proved more precise. The IASP algorithm is applied to execute the phase retrieval to derive the aberrations of optical systems from intensity profiles measured in the observation plane. The derived aberrations are fitted by Zernike polynomials under the constraint that the wavefront aberrations are smooth. Numerical simulations are performed to test the accuracy of this method.