The accuracy of the Shack–Hartmann wavefront sensor for measuring wavefront aberrations is mainly dependent upon the measuring accuracy of the centroid of each spot. An effect of the aperture of the 4F system on the correlation properties of speckle patterns produced with monochromatic light is investigated at the Shack–Hartmann sensor plane and at the focal plane of the sensor. An expression for a speckle patterns correlation length changing due to the extended aperture of the 4F system is derived by Fourier optics method. The experimental results that confirm the theoretical dependence quality within the limits of errors are obtained, and it is shown that the spatial finiteness of the optical system causes significant changes of transferred aberrated field.
The possibilities of wavefront curvature measuring by Talbot sensor are theoretically and experimentally investigated. A new method of wavefront aberrations measurement is proposed and demonstrated. It is based on the observation of the Talbot effect when the diffraction grating is adapted to the wavefront curvature of the analyzed wave. Herewith, the observation plane stay fixed and corresponds to the Talbot length for a plane wave. It is shown that the measurement range can be made several times wider, with the help of the adaptive Talbot sensor, by retaining the required angular sensitivity. A possibility of self-reproduction of the rectangular grating (with different periods along the axes) by the astigmatic wavefront is experimentally demonstrated. The possibility of the experimental realization of the adaptive Talbot sensor using the dynamic spatial light modulator is demonstrated.
The self-imaging phenomenon, or the Talbot effect, is diffraction and interference effect for coherent light that is transmitted through infinite grating or other periodic structure. But in practice, intensity distribution is reproduced with some distortions due to finite size of a grating. The influence of aperture effects on quality of wavefront reconstruction by the sensor based on the Talbot effect is considered in this work. 2D binary and gray-scale amplitude gratings with different periods and form of holes were used as the input element of the sensor. Computer simulation for different aberrations and varying aperture size was performed. The experimental results of comparative analysis of wavefront measurements by the diffraction Talbot sensor with a finite aperture and the Shack-Hartman sensor are presented.
We propose holographic wavefront sensor based on the Talbot effect. Optical wavefronts are measured by sampling the
light amplitude distribution with a two-dimensional periodic holographic grating. The factors that allow changing an
angular measurement range and a spatial resolution of the sensor are discussed. A comparative analysis with the Shack-
Hartmann sensor is illustrated with some experimental results.
Results of theoretical calculations of angular dependence of the phase incursions for s- and p- orthogonal components of
optical wave reflected by the surface with variable refractive index is discussed. The possibility of determining the
spatial distribution refractive index from the wavefront measurements was experimentally shown.
Application of the Shack-Hartmann sensor with holographic lenslet array is offered for wavefront aberrations
measurements in speckle field. The main feature of the method is that the tested wave front can be compared with the
arbitrary wave front preliminary recorded to holographic memory of the array. The sensor iterative work algorithm for
measuring of the variable speckled wave fronts is offered. Experimental results of the curvature measurements for
spherical speckled wave are presented. The possibility to use the method proposed for surface deformation analysis is
shown.
The modification of the wavefront registration scheme for the purpose of the sensor spatial resolution improvement is
considered. It's proposed to use the focused laser beam for illumination of the separate area of the surface, which after
the optical transformation in Fourier optics scheme forms the signal in the sensors plane that is proportional to the
spectrum of the spatial frequencies of the surface shape. At the same time the spatial resolution in the surface plane is
determined by the sensor aperture, but not the spatial resolution of its lenslet array. The theoretical analysis and computer
simulation of the wavefront sensor work for the local inhomogeneities determination of thereflective surface is realized.
For obtaining the submicron spatial resolution of the sensor it is proposed to classify the surface micro areas by the
multidimensional statistical analysis methods.
A nonlinear holographic lenslet array is used to extend the angular dynamic range of a Shack-Hartmann wavefront sensor. The lenslet array has two focal distances defined by the first- and second-order diffracted beams. The second-order beam channel is used for preliminary estimation of the spot position in the first-order beam channel. The sensor has an angular dynamic range twice as large as that of a sensor with single-focus lenslets, while retaining the same accuracy.
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