Study of field intensity distribution of laser beam propagating through a micro-lens array

The propagation of a laser beam through a micro-lens array (MLA) was simulated using Finite Time Difference Domain (FDTD) method. The intensity distribution at different output planes away from the micro-lens array surface was investigated. As compared to the focal plane, the intensity distribution observed at those out-of-focus planes varies, which is attributed to the interference and diffraction of output laser beams. The simulated results were counter checked by placing a physical MLA under an illumination of a 488 nm continuous wave Argon Ion laser and images were captured for different output planes. Both simulation and experimental results show a great similarity in terms of the distribution patterns. By changing the lens sag height with respect to the lens diameter, the full width at half maximum (FWHM) of the focused laser spot and its corresponding maximum energy flux were analyzed. A FWHM of 160 nm can be achieved by proper selection of lens sag height. It is also found that the energy flux is proportional to numerical aperture (NA).