Study On Multi-step Zone Plate Array Laser Beam Homogenizer Based On Random Phase Control

The light spot with uniform light intensity needs to be obtained in the fields of laser processing,lithography,laser medicine and so on.In order to meet the requirements of beam quality in various fields,the laser spot with Gauss intensity distribution is needed to form the flat top distribution.The beam homogenization technology is derived from it.At present,there are various beam homogenization methods,the micro-lens array has many advantages with a high uniformity,good adaptability,high transmission,and high energy efficiency.However,there are two main disadvantages: 1)The decrease in uniformity of the target plane suffers from interference fringes generated by multi-beam interference,due to the periodic distribution of a Fresnel microlens array and the coherence of single-mode Gaussian laser beams.2)The microlens array has a dead zone and the fill factor is not high.3)Due to the limitations of the processing technology level,the microlens array cannot be miniaturized.To eliminate the multi-beam interference,a binary and randomly distributed phase was introduced to the Fresnel lens array and a binary phase change of 0 or ? is applied to individual Fresnel lens.This change in phase disrupts the phases of the periodic beams,and therefore reduces the effect of multi-beam interference on the homogenized plane.The numerical simulation of the laser beam homogenization were carried out using the Fresnel lens with an aperture of 0.5 mm and the foci of 6 mm,and the array number of 20×20.The simulation results show that the overall uniformity of the target plane is calculated as 90% and the beams energy efficiency can be up to 96%.The designed Fresnel lens array was fabricated using microelectronic technologies.The measured uniformity of the homogenized laser beams at a wavelength of 1 064 nm was 83%,and the beams energy efficiency was 96%.Our results indicate that the introduction of the binary and randomly distributed phase to the periodic microlens array can effectively decrease the influence of interference and improve the uniformity of homogenization of single-mode Gaussian beams.