Wavefront sensor has been widely used for various research fields. Among these wavefront measuring techniques, Shack-Hartmann wavefront sensor has the merit of simple structure, real-time detection and wide waveband. Traditional Shack-Hartmann wavefront sensor is usually based on geometrical optics, which builds a micro-lens array in front of a CMOS sensor. Here amplitude-only photon-sieve array was proposed to replace the micro-lens array to reduce the cost and simultaneously to improve the measurement accuracy by super-resolution focusing of test wavefront. A simulation experiment was carried out through software GLAD and another optical experiment was implemented by Liquid crystal spatial light modulators (LC-SLM) to verify the effectiveness. As a kind of amplitude-only diffractive lens, largeaperture photon-sieve array can be easily fabricated by lithography, which has great potential to be applied for measurement of large-scale laser beam and optical element.
Coherent diffractive imaging (CDI) is a lensless, high-resolution imaging method. In order to overcome the problems of poor-quality image and slow convergence of iterative algorithm in traditional CDI, here multimode fiber source is selected as the lighting source to replace the traditional plane-wave. A phase-only spatial light modulator (SLM) is used as a negative lens instead of a positive lens in a 4f imaging unit. The diffraction field can be rapidly changed at a very short distance so as to realize a fast convergence and then save a lot of iteration times. This proposed setup has advantages such as a simpler structure and static recording. Both simulations and visible-light experiments demonstrate the good imaging quality and robustness of this method.
Radial-shearing digital holography has been proposed to reconstruct the wavefront of test object in a common path, which can take use of a bifocal diffractive lens to realize radial-shearing interference. For coherent light source, the recording plane is usually located near the focal point in order to reduce the crosstalk. As for incoherent light source, on the one hand, the above recording cannot take advantage of the space-bandwidth product of optical detector, and on the other, the optical path length is far greater than the coherent length of the light source, which results in failure of effective interferogram. A high contrast interferogram must meet the requirement of nearly equal intensity between the two interference beams. Based on this viewpoint, a better recording plane for radial-shearing holography is in the middle location between the two images. Compared to the recording location with equal beam diameter, the midpoint of the two images is a better choice to improve the image quality on condition that one focal length is much greater than the other. Otherwise, this difference will gradually decrease as one focus is close to the other. The experiment was carried out to verify the validity of our proposed method.
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