In this paper, we generalize the concept of classical spiral zone plates (SZPs) to fractional spiral zone plates (FSZPs). By using an SZP with a fractional topological charge and controlling the starting orientation, we can break down the symmetry of the focusing process to give orientation-selective anisotropic vortex foci. Numerical results show that its binary structure gives additional high-order foci on the optical axis and the intensities in the foci can be controlled by properly choosing the fractional topological charge. Our study reveals the feasibility to control the intensity in the foci by means of FSZPs.
We present a realization of the sinusoidal transmission function using a series of zigzag-profiled strips where the transmission takes on the binary values 0 and 1 in a two-dimensional distribution. A zigzag transmission grating of 1000 line/mm has been fabricated and demonstrated on the soft x-ray beam of synchrotron radiation. The axial single-order diffraction indicates that the zigzag transmission grating is adequate for spectroscopic application.
Laser plasma experiments, which demonstrated the single order diffraction property of spectroscopic photon sieve (a novel single-order diffraction grating), were performed on the SILEX-I femto-second laser facility. High-intensity laser radiation was focused onto a Cu target to generate plasma. The spectra of soft X-ray from copper plasmas have been measured with spectroscopic photon sieve based spectrograph. The results show that the spectroscopic photon sieve is able to provide soft X-ray spectrum free from higher-order diffraction components. The measured spectra obtained with such a spectroscopic photon sieve need no unfolding process to extract higher-order diffraction interference.
A single-order diffraction transmission grating named spectroscopic photon sieve (SPS) for soft x-ray region is proposed and demonstrated in this paper. The SPS consists of many circular pinholes located randomly, and can realize both free-standing diffractions and the suppression of higher-order differations. In this paper, the basic concept, numerical simulations, and calibration results of a 1000-lines/mm SPS for soft x-ray synchrotron radiation are presented. As predicted by theoretical calculations, the calibration results of a 1000-lines/mm SPS verify that the higher-order diffractions can be significantly suppressed along the symmetry axis. With the current nanofabrication technique, the SPS can potentially have a higher line density, and can be widely used in synchrotron radiation, laser-induced plasma diagnostics, and astrophysics.
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