Ga₂O₃ thin films were fabricated by the electron-beam evaporation technique at a varying oxygen partial pressure from 0 to 2.0 × 10⁻² Pa. The effect of oxygen partial pressure on the crystalline structure and optical properties of the Ga₂O₃ films was analyzed using sophisticated techniques including X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, spectroscopic ellipsometry, ultraviolet-visible spectroscopy and a laser-induced damage test system. The correlation between the oxygen partial pressure and the film’s properties in optics and materials were investigated. XRD and Raman revealed that all films were amorphous in spite of applying a varying oxygen partial pressure. With the change of oxygen partial pressure, XPS data indicated that the content of oxygen in the Ga₂O₃ films could be broadly modulable. As a result, a changeable refractive index of the Ga₂O₃ film is realizable and a variable blue-shift of absorption edges in transmittance spectra of the films is achievable. Moreover, the damage threshold value varied from 0.41 to 7.51 J/cm² according to the rise of oxygen partial pressure. These results demonstrated that the optical properties of Ga₂O₃ film can be broadly tunable by controlling the oxygen content in the film.

The off-axis conic aspheric surface is widely used as a component in modern optical systems. It is critical for this kind of surface to obtain the real accuracy of the shape during optical processing. As is widely known, the null test is an effective method to measure the shape accuracy with high precision. Therefore, three shape measurement methods of null test including auto-collimation, single computer-generated hologram (CGH), and hybrid compensation are presented in detail in this research. Although the various methods have their own advantages and disadvantages, all methods need a special auxiliary component to accomplish the measurement. In the paper, an off-axis paraboloid (OAP) was chosen to be measured using the three methods along with auxiliary components of their own and it was shown that the experimental results involved in peak-to-valley (PV), root-mean-square (RMS), and shape distribution from three methods were consistent. As a result, the correctness and effectiveness of these three measurement methods were confirmed, which are very useful in engineering.

When utilizing the Gerchberg-Saxton (GS) algorithm to design diffractive optical elements, correction coefficients are introduced to improve the quality of the design results. The main design idea is to correct the target information dynamically during the iterative calculation process. The effectiveness of the proposed method is demonstrated through the verification of beam shaping and phase-type hologram designs. Compared to the traditional GS algorithm, the results of beam shaping show that the light intensity nonuniformity and the root-mean-square error (RMSE) of the shaped spot are reduced by an order of magnitude. The results of phase-type holograms show that the reconstructed image's peak signal-to-noise ratio (PSNR) is improved by about 12 dB. Finally, the paper also discusses the selection of correction coefficients, providing insights into the selection of optimal design correction coefficients. The simulation and experimental results show that the improved algorithm proposed in this paper is not only simple in design but also highly efficient in obtaining a high-quality phase structure, which is of great help in designing high-quality diffractive optical elements. (c) 2024 Optica Publishing Group

The inherent “grid” effect of LC-SLM in holographic displays can lead to issues such as the presence of zero-order spots and multi-level diffraction images, resulting in a decrease in the quality of reconstructed images. In this Letter, a dual light source compensation method is proposed to address this problem. By analyzing the influence of the LC-SLM “grid” effect on the diffraction field and the rule of change of light intensity distribution and position of the reconstructed image, the dual light source is introduced on the basis of the rule of change of energy distribution at the symmetric position of the reconstructed image so as to compensate for the quality of the display results. The results show that the method not only avoids the influence of zero-order spot and multi-level diffraction image on the holographic display results but also especially highlights that the uniformity of light energy distribution of the reconstructed image is greatly improved, which provides a reference for LC-SLM to perform a higher-quality holographic display.

In this paper, to improve the optimization capability of the simulated annealing algorithm (SA) in the optimal design of diffractive structures, the random fluctuation problem in the algorithm is investigated, and a new fluctuation calculation model is proposed. The optimal design of phase-type diffraction gratings and beam-shaping devices verified the fast accuracy of the proposed model. The simulation experimental results show that the model’s introduction is particularly significant in substantially reducing computation time (a threefold increase in computation speed) and improving the algorithm’s optimization finding capability. Finally, the setting of the model parameters is discussed analytically to make the proposed model more applicable and robust. The study results provide guidance and assistance for higher speed and effectiveness in the optimal design using simulated annealing algorithms. It can be applied to any complex and large-scale optimization calculation problem.