Polarization smoothing (PS) can effectively improve the uniformity of the focal spot by changing the polarization distribution of the beam. In this paper, a technical scheme for achieving multidimensional PS by cascading birefringent wedge (BW) has been proposed. A near-field and far-field diffraction transmission model with multiple PS and a continuous phase plate (CPP) was first constructed, and parameters such as the wedge angle and placement position of BW are optimized through theoretical analysis to increase the number of sub-focal spots on the target plane and change the distribution direction. Then one-dimensional (1-D) power spectral density (PSD) and root mean square (RMS) were used to quantify the difference in the focal spot uniformity in different directions, the results show that the cascaded BW not only ensures the smoothing effect of a single BW, but also has a smoothing performance in a specific frequency band at specific wedge angles.
High-power laser systems have high requirements on the size, shape, and uniformity of the focal spot. Both continuous phase plate (CPP) and lens array (LA) can be used for beam shaping and smoothing. However, their ability is limited and there are few studies on the cooperation of CPP and LA. In this paper, the joint design of the CPP and LA was proposed, we theoretically analyzed its principle and studied the method to achieve better shaping and smoothing performance. Then, the far-field focal spot properties of three beam smoothing methods of the LA, the CPP, the CPP combined with the LA were obtained and compared through numerical simulation. The result shows that the LA is mainly contribution to shaping and the CPP mainly reduces the high-contrast intensity modulation to a certain extent. The joint design of the CPP and the LA greatly improves the uniformity of the far-field focal spot, which is valuable for expanding the application scope of the CPP and the LA.
The crosstalk problem between the background light and the signal light of the diffractive optical element severely degrades the image quality and limits the practical application. In this paper, we proposed an off-axis imaging technology aimed at multifocal diffractive lenses and performed geometrical imaging analysis to investigate the imaging distribution. Off-axis imaging ensured a high signal-to-noise ratio by separating the signal and the noise spatially and provided a larger space for parallel synchronization processing in different image plane. Taking the bifocal Greek-ladder lens as an example, the experiment achieved zero-crosstalk multiplanar images and verified the law of diffractive imaging. Besides, the critical condition for zero-crosstalk imaging was also studied.
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