A noniterative method for dynamic X-ray phase imaging from the recorded far-field diffraction intensity distribution of the object wavefront, sampled by a sampling plate, is proposed. The sampling plate consists of a two-dimensional (2D) aperture array and a central reference aperture. In this method, the complex amplitude of the object wavefront, especially the phase that carries the inner refraction information, can be retrieved from the inverse Fourier transform of the diffraction intensity distribution by directly filtering with a same aperture array. As this method requires only a single measurement of the diffraction intensity pattern and does not need any iterative algorithm, in principle, it provides a practical approach for dynamic phase imaging in a wide range of wavelengths. The experimental results demonstrated that the proposed method is practicable. The proposed may have potential application in high-efficiency phase retrieval for coherent diffraction imaging and phase contrast imaging.
In the paper, a 45 degree TFBG was fabricated in photosensitive fiber successfully using phase mask technique. The polarization-dependent loss characteristic of the TFBG was experimentally researched in the paper using a special measurement system. The measurement results showed that the 45 degree TFBG could act as a polarization possession element. Based on the 45 degree TFBG, a linearly-polarized Yb-doped fiber laser was demonstrated. The polarization-extinction ratio of the output laser is about 30 dB. The output power was about 13 mW with the pump power of 100 mW. The central wavelength of the laser is 1064nm and the wavelength bandwidth was about 0.7nm. Being a polarization device, the TFBG has the advantages of in-fiber, compact, good polarization capability and low price.
Numerical experiments are carried out about the temporal and spatial variation of branch points by four-dimension code of laser propagating in atmosphere. The theory of branch-point detection and phase reconstruction is introduced. The act of branch points' creating and annihilating is emulated when the light wave propagating in atmosphere. The evolvement of branch points in some propagating range with time is emulated, too. The behavior of branch points in the distorted optical field is simulated when the main laser and beacon laser propagate in the atmosphere with opposite direction at the same time. The work could provide a reference for further study of laser propagation through atmosphere and adaptive optics system.
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