Research On Imaging Characteristics Based On Vortex Light

Optical vortices is a helical phase structure of light field. It has many potential applications especially in optical micromanipulation, biomedicine, quantum communication and so on, because of its unique ring light intensity and photon orbital angular momentum. Now optical vortices becomes an important branch in the study of modern optics. This paper mainly studies on imaging application by using vortex beam. It is experimentally verified that the spiral phase and doughnut intensity could be used to improve the quality of object imaging.The basic theory of vortex beam is discussed in this paper, including its basic concept and several commonly generation methods. Then the characteristics of vortex beam interference with the plane wave and spherical wave are analyzed respectively by the theory of holographic interferometry. And they can be applied to detect the topological charge of vortex beam and generate vortex beam by computer-generated hologram. Finally the propagation of vortex beam is numerical simulated and it makes the dark-field imaging illuminated by vortex beam feasible.The spiral phase filter is introduced by the radial Hilbert transform in the paper. A 4f optical imaging system is simulated in computer. After that, the amplitude and phase objects can be filtered numerically by the system. Then the difference between cosine grating and blazed grating impacting on spiral phase filter is revealed by simulation. The conclusion is the blazed grating is better than cosine grating, and it is proved by the experiment results. Besides, we find the spiral phase filter is also better than dark-field filter by experiment.We propose a dark-field digital holographic microscopy (DHM) by using vortex beam illumination. In the paper, the annular illumination of vortex beam and the dark-field DHM imaging system are combined. The corresponding DHM imaging system is established. The polystyrene spheres each with a size of 690 nm are utilized as objects in the experiment. By comparing the results of reconstructed images under bright-field illumination with those under dark-field illumination DHM, it is proved that the resolution of dark-field DHM is improved and the contrast of its reconstructed image is enhanced accordingly. In the meantime, we realize the dark-field imaging of large objects by vortex beam and ordinary lens, and it improves the quality of imaging equally.