A randomly distributed freeform cylindrical microlens (RFCML) is proposed for laser beam reshaping and homogenization. By introducing a freeform surface in the microlens, the optical field can be controlled with the expected distribution with a single interface. With the help of randomly distributed subapertures of the microlens, the diffraction orders of the microstructure are smoothed and the optical field is homogenized in the far field. The theoretical design of the RFCML is carried out, and the influence of the field smoothing with the random coefficient is analyzed. With the optimized results, the device is fabricated with the laser beam direct writing method and demonstrates the excellent property of laser beam homogenization in the device. The experimentally reshaped homogenized line with a full angle of 40 deg is in good accordance with the theoretical results.
The random antireflective structures are modeled by the analysis of the random morphology distribution. According to the effective medium theory, the transmission of the antireflective structure is calculated by dividing the structure into multilayer, and the dependence on parameters of the subwavelength is analyzed in detail. In the single-variable condition, etching depth, half breadth of distribution, and median of distribution get a positive correlation with the transmittance where the etching depth plays a most important part in enhancing the transmittance, whereas the angle of structures gets a negative correlation. The experimental results coincide well with the calculation and analysis. The analysis offers a theory guidance to fabricate random subwavelength antireflected structures using metal dewetting.
A theoretical model is proposed to analyze the fabrication of metal nanopartical resist by metal nanofilm annealing, which is used in the manufacture of the transmission-enhanced subwavelength structures at the interface of the optical glass. Based on the conservation of volume of the metal before annealing and after heat treatment, the theoretical relationships of the structure parameters between the metal nanofilm and the metal nanoparticles are obtained. The experimental results coincide well with the theory model, which offers a theoretical guidance to fabricate subwavelength antireflected structures with the advantage of low cost achieved through metal nanofilm annealing. By this means, the average transmission of the quartz device intensifies to 97.9% for the structures fabricated on the both sides compared with the 93% for the unstructured one.