Objective  In traditional laser interference systems, the far-field spot must simultaneously satisfy two requirements: the spot size should cover the entire target cross-section, and the spot power density must exceed the energy threshold for detector interference. When the target cross-sectional area is large, these two requirements present an inherent contradiction. Conventional focused single-spot systems often attempt to resolve this by increasing the total output laser energy, which imposes extremely high demands on system fabrication and cost. To overcome this contradiction, a novel laser interference method based on Dammann grating beam splitting and scanning synthesis is proposed.

Methods  Dammann gratings with beam splitting ratios of 5×5 and 25×25 are used to convert an incident laser beam into regular two-dimensional spot arrays (Fig.2). Through an angular scanning mechanism (Fig.5), far-field uniform surface spot synthesis is achieved. The influence of grating imaging quality on the energy uniformity of the synthesized spot is first explored. Then a scheme is proposed to improve illumination uniformity of low-quality gratings by optimizing the scanning area overlap strategy. The intensity uniformity of far-field spots obtained under different scanning schemes is quantitatively analyzed using the coefficient of variation of intensity (I_CV). Numerical simulations are conducted to compare the performance of the two gratings under various scanning lengths and overlap conditions.

Results and Discussions  It is found that the quality of the Dammann grating directly affects the characteristics of the two-dimensional spot array, including uneven spot intensity, irregular spacing, and the presence of sidelobe structures. These imperfections consequently influence the intensity uniformity of the far-field spot after scanning. The 5×5 Dammann grating used in the simulation exhibits relatively good imaging quality. When the scanning length is set to the average spot array spacing, the I_CV of the far-field spots is 6.38% (Fig.6), indicating good uniformity. In contrast, the 25×25 Dammann grating used in the simulation has relatively poorer imaging quality. When the scanning length equals the average spot array spacing, the I_CV is 20.66% (Fig.9). However, when the scanning length is increased to twice the average spot array spacing, the I_CV decreases to 10.27% (Fig.10). When the scanning length is further increased to twice the total length of the spot array, the I_CV becomes as low as 1.76% (Fig.11). These results demonstrate that by adjusting the scanning length to cause overlapping of the scanning areas of adjacent spots, the uniformity of the post-scanning spot can be significantly improved. The optimal overlap strategy effectively compensates for non-uniformities arising from poor grating quality, achieving a 20-fold enhancement in spot uniformity.

Conclusions  A new laser area interference method based on the combination of Dammann grating beam splitting and angular scanning is proposed. This method effectively resolves the inherent contradiction between spot size and energy density in traditional laser interference systems. Under the same incident energy, it enables effective interference over a larger spatial range; for the same spatial coverage requirement, it significantly reduces the required laser energy. For Dammann gratings with different beam splitting ratios, the scanning time for a 25×25 grating is approximately (1.05)² times that of a 5×5 grating, while the synthesized spot area increases by a factor of 5². This indicates that high-resolution gratings offer greater efficiency advantages in large-area interference applications. The scanning synthesis outcome is sensitive to grating quality, which can be inversely used to evaluate the uniformity of Dammann gratings. By optimizing the scanning range and overlap strategy, the non-uniformity of low-quality gratings can be effectively compensated. From an application perspective, this method possesses both directional irradiation and area coverage capabilities, making it suitable for various tactical scenarios. The results provide new ideas and theoretical foundations for the engineering development of future laser interference systems.