Structures smaller than the wavelength of light or electromagnetic waves, appropriately designed to control optical response, are called meta-optics or metamaterials and have recently attracted attention as a way to realize ultra-thin and functional optical components. Our research group is working in two directions to extend the possibilities of these electromagnetic meta-structures. Until now, lithographic techniques have been mainly used to fabricate nanoscale or microscale artificial structures smaller than the wavelength of electromagnetic waves. However, this has been problematic because it requires a clean-room environment and expensive equipment. We have recently succeeded in fabricating moth-eye anti-reflective structures and meta-lenses using state-of-the-art ultrashort pulsed laser processing with performance comparable to ones fabricated by lithography. This has the potential to simplify meta-structure fabrication methods dramatically. The second is meta-optics that operate in the vacuum ultraviolet region, where the wavelength is shorter than 200 nm. Although there are still very few meta-optics in this wavelength region, we have found that it is possible to convert the wavelength of the visible laser to vacuum ultraviolet light and control its polarization by fabricating meta-structures on freestanding dielectric thin films (nanomembranes). This can potentially become a new platform for creating vacuum ultraviolet photonics. In this seminar, I will introduce these recent research topics in our group.

Simulating wave propagation in complex structures can be extremely computationally expensive, taking hours, days or even weeks. In addition, many of the commonly used techniques suffer from accumulating errors called numerical dispersion, which can cause a relative error of 100% after propagating a few dozen of wavelengths already.

WAVESIM is a new approach that is both orders of magnitude faster and orders of magnitude more accurate than commonly used finite difference and pseudospectral time domain methods. WAVESIM does not use any finite difference approximations and thus does not duffer from numerical dispersion. Our method is based on the infinite Born series known in scattering physics. Unlike the original Born series, however, our method is guaranteed to converge monotonically to the correct answer.

I will introduce the basic idea of our method, and discuss its strengths and limitations. In addition, I will show some examples of how to use our user-friendly MATLAB code to perform simulations of the Helmholtz and Maxwell’s equations. Our open source code can use the CPU, or use the MATLAB-provided GPU acceleration. Recently, in collaboration with RayFos Ltd, WAVESIM now includes customized CUDA acceleration that provides an additional 80% speedup of the simulations.

With WAVESIM, simulations that took hours now take minutes. We invite you to come to the seminar and to try the open source code yourself. We are currently looking for collaborators and users, and we are happy to help you get started with our software.