Designing a metacomponent to shape a Gaussian beam to a 1D 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 1D 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 1D rectangular top hat in the far field from a Gaussian incident beam.
Input Gaussian beam
Designing a 1D rectangular top hat
Wavefront designed to transform a Gaussian beam into a uniform intensity profile along one spatial dimension.
Parameters for a 1D rectangular top hat
# create tophat based on https://doi.org/10.1016/j.optcom.2020.125313
Analysis
Top hat far field based on 1D NFWF design [2]
Expected result for the 1D rectangular top hat design
Applications
Beam shaping with metaoptics enables the transformation of a Gaussian beam into a highly uniform 1D rectangular (line-shaped) top hat profile. By precisely engineering the phase distribution at the nanoscale, metasurfaces create sharp intensity edges and homogeneous energy distribution along a defined line. This ensures controlled thermal input, improved processing stability, and higher efficiency in line-based laser applications.
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] Abbaszadeh, M. Ahmadi-Boroujeni and A. Tehranian, A compact polarization insensitive all-dielectric metasurface lens for Gaussian to tophat beam shaping in sub-terahertz regime, Optics Communications (2020) https://doi.org/10.1016/j.optcom.2020.125313.
[3] Liu, Che, and Yanling Guo. “Flat-top line-shaped beam shaping and system design.” Sensors 22.11 (2022): 4199. https://www.mdpi.com/1424-8220/22/11/4199
[4] Zhu, Hongbo, et al. “The conversion from a Gaussian-like beam to a flat-top beam in the laser hardening processing using a fiber coupled diode laser source.” Optics & Laser Technology 125 (2020): 106028. https://www.sciencedirect.com/science/article/abs/pii/S0030399219311661
