Influence on wide-angle doublet metalenses due to different types of all-dielectric metasurfaces.

It has been shown in previous literature that nearly diffraction limited focusing is possible by a doublet metalens up to almost 30 deg. This result indicates that metalenses can work well, even at oblique incidence. Although various meta-atoms have been proposed, as far as we know, there is no report that compares what kind of meta-atom is robust against oblique incidence. Here, we first numerically calculated the incident angle dependence of the three types of meta-atoms. The results show that the waveguide-type structure is the most robust to oblique incidence. Next, we performed rigorous electromagnetic simulations for the cylindrical doublet metalenses to compare the micropost type and waveguide type. These results indicate that a waveguide-type metasurface further improves the off-axis performance of the doublet lens previously introduced.

Angular spectrum calculations for arbitrary focal length with a scaled convolution.

Nyquist sampling theorem in an image calculation with angular spectrum method restricts a propagation distance and a focal length of a lens. In order to avoid these restrictions, we studied suitable expressions for the image computations depending on their conditions. Additionally, a lateral scale in an observation plane can be magnified freely by using a scaled convolution in each expression.

Method for designing phase-calculation algorithms for two-dimensional grating phase-shifting interferometry.

We propose a design method of phase-analysis algorithms based on two-dimensional grating phase shifting for Talbot interferometry, Talbot-Lau imaging, or the Ronchi test. These algorithms are designed to separate the two orthogonal shearing wavefronts and eliminate error effects of unwanted diffraction orders, simultaneously. Taking the effect of multidiffraction into account, moving the two-dimensional grating along a certain pass leads to a series of phase-shifted interfrograms, from which two orthogonal shearing wavefronts are derived, for the tested wavefront to be retrieved. The designing process is demonstrated, and the residual errors are analyzed via simulation works and experimental comparison.

Wavefront measurement interferometry at the operational wavelength of extreme-ultraviolet lithography.

Two basic types of interferometer, a point diffraction interferometer (PDI) and a lateral shearing interferometer (LSI) suitable for operation in the extreme-ultraviolet (EUV) wavelength region, are described. To address the challenges of wavefront measurement with an accuracy of 0.1 nm rms, we present a calibration method for the PDI that places a mask with two large windows at the image plane of the illumination point light source and a general approach to deriving the phase-shift algorithm series that eliminates the undesired zeroth-order effect in the LSI. These approaches to improving the measurement accuracy were experimentally verified by the wavefront measurements of a Schwarzschild-type EUV projection lens.