Large-range lithography nano-alignment without phase unwrapping by a dual-frequency moiré fringe heterodyne.

Moiré fringe is an effective approach to realize nano-alignment. However, affected by short periodicity and phase unwrapping, moiré fringe technology has small alignment ranges and redundant algorithms, making it difficult to meet practical application requirements. To solve the problem, we propose a large-range lithography nano-alignment method without phase unwrapping by a dual-frequency moiré fringe heterodyne. This method obtains four sets of moiré fringes from the main and differential alignment marks and then calculates the misalignment information using the heterodyne method. In this approach, both large alignment range and high alignment accuracy are achieved while avoiding the phase unwrapping process. The experimental results verified the rationality and feasibility of the proposed method.

Efficient Fourier single-pixel imaging based on weighted sorting.

Fourier single-pixel imaging (FSI) has attracted increased attention in recent years with the advantages of a wide spectrum range and low cost. FSI reconstructs a scene by directly measuring the Fourier coefficients with a single-pixel detector. However, the existing sampling method is difficult to balance the noise suppression and image details within a limited number of measurements. Here we propose a new sampling strategy for FSI to solve this problem. Both the generality of the spectral distribution of natural images in the Fourier domain and the uniqueness of the spectral distribution of the target images in the Fourier domain are considered in the proposed method. These two distributions are summed with certain weights to determine the importance of the Fourier coefficients. Then these coefficients are sampled in order of decreasing importance. Both the simulations and experiments demonstrate that the proposed method can capture more key Fourier coefficients and retain more details with lower noise. The proposed method provides an efficient way for Fourier coefficient acquisition.

High-order spatial phase shift method realizes modulation analysis through a single-frame image.

For the modulation-based structured illumination microscopy system, how to obtain modulation distribution with an image has been a research hotspot. However, the existing frequency-domain single-frame algorithms (mainly including the Fourier transform method, wavelet method, etc.) suffer from different degrees of analytical error due to the loss of high-frequency information. Recently, a modulation-based spatial area phase-shifting method was proposed; it can obtain higher precision by retaining high-frequency information effectively. But for discontinuous (such as step) topography, it would be somewhat smooth. To solve the problem, we propose a high-order spatial phase shift algorithm that realizes robust modulation analysis of a discontinuous surface with a single-frame image. At the same time, this technique proposes a residual optimization strategy, so that it can be applied to the measurement of complex topography, especially discontinuous topography. Simulation and experimental results demonstrate that the proposed method can provide higher-precision measurement.