Designing a metacomponent to shape a Gaussian beam to a 2D rectangular top hat.
Introduction
- In many DOE-based beam shaping systems, a Gaussian input beam is reshaped into a required intensity. The performance of this conversion depends on how the input beam fills the optical aperture.
- A Gaussian beam has a finite beam waist and a radially varying intensity profile. If the beam diameter is smaller than the lens aperture, the lens in underfilled.
- When a lens is underfilled, the effective NA is reduced and the focal spot will broaden (in plane as well as the focal depth) [1]
Goal
To create a 2D rectangular top hat intensity profile from a Gaussian beam based on analytic NFWF.
Outline
NFWF designed lens with focal spot of 500 µm (idealised metacells)
Metacell design
The metasurface unit cell consists of SiO2 pillars with a lateral period of 250 nm. The height is swept between 100 and 1500 nm.
Creating metacomponents
A metacomponent is created after analysing and importing the optimised metaatoms.
A 500 µm × 500 µm metasurface is then defined.
The structure is illuminated by normally incident, TE polarised Gaussian beam at 550 nm.
Design
Here, the near field wavefront (NFWF) was designed to generate a 2D rectangular top hat in the far field from a Gaussian incident beam.
Input Gaussian beam
Designing a 2D rectangular top hat
Wavefront designed to transform a Gaussian beam into a uniform 2D rectangular top hat.
Parameters for a 2D rectangular top hat
# create tophat based on https://doi.org/10.1016/j.optcom.2020.125313
Analysis
Analysis: 2D rectangular top hat
Expected result for the 2D rectangular top hat design
Applications
Metaoptical beam shaping allows the generation of a uniform 2D rectangular top-hat intensity profile with sharp boundaries and minimal intensity roll-off. Compared to Gaussian illumination, this flat-field distribution eliminates hot spots and enhances quantitative accuracy. The ultra-thin and integrable nature of metaoptics enables compact illumination modules for advanced imaging and material processing systems.
References
[1] Yajun Li and Emil Wolf, “Three-dimensional intensity distribution near the focus in systems of different Fresnel numbers,” J. Opt. Soc. Am. A 1, 801-808 (1984) https://doi.org/10.1364/JOSAA.1.000801
[2] Le, Hoang, et al. “Effects of top-hat laser beam processing and scanning strategies in laser micro-structuring.” Micromachines 11.2 (2020): 221. https://doi.org/10.3390/mi11020221
[3] Khaw, Ian, et al. “Flat-field illumination for quantitative fluorescence imaging.” Optics express 26.12 (2018): 15276-15288. pubmed.ncbi.nlm.nih.gov/31729201/
[4] Kabir, Mohammad M., et al. “Demonstration of flat-top beam illumination in widefield multiphoton microscopy.” Journal of Biomedical Optics 25.1 (2020): 014503-014503. https://doi.org/10.1117/1.JBO.25.1.014503
