When using interference wave front to detect density field, it is better to have an interference system which is small and
compact so that different directions of wave fronts can be obtained to reconstruct the density field to be detected. A twodimensional
CGLSI (Cross Grating Lateral Shearing Interferometer) system which consists of a two-dimensional cross
grating and a two-dimensional order-selecting window used as a filter is presented in this paper. Lateral shearing
interferogram of two orthogonal directions (X and Y) each other can be obtained by using this system. With the
advantage of anti-vibration and no reference surface, lateral shearing interferometer is suitable to inhibit external
environment disturbance. In this paper, analysis and simulations have been conducted on grating constant from
geometrical optics and physical optics using Fresnel approximation method respectively based on lateral shearing rate,
windows’ distance in two-dimensional order-selecting window and layout of the system which concludes the best option
for grating constant is d = 25μm . The most optimized design of size and distance for windows in two-dimensional
order-selecting window has been carried out on the basis that complex amplitude distribution can go through the filter so
that there is no distortion on wave front. All designs have gone through computer simulation and fit into the requirements
for the designs.
In this article, an interference digital testing method for measuring spatial density distribution of transmissive objects is
presented. This method applies a radial shearing interferometer to test the density field from 8 projections in the same
plane. By taking advantage of the regularized phase-tracking technique (RPT), the single interferogram will be
demodulated to two-dimensional phase distribution of the corresponding projection beam. Then the phase data on one
given cross-section of every projection is selected to form 8 curves, which describe one-dimensional phase variation on
the given cross-section from each projection. Regarding these curves as computer tomography projection data, the
refractive index distribution of the given cross-section can be reconstructed utilizing the algebraic reconstruction
technique (ART). Thus, a three-dimensional distribution of refractive index can be obtained by applying the method
above to different cross-sections in order. Finally, we are capable of calculating the spatial density distribution with the
relation between density and refractive index of the substance tested. In addition, the density field testing for hypersonic
flow field is investigated as an example in this article. Considering the fact that the target model in the optical window
center of a wind tunnel will inevitably block some testing beams, which will lead to the sharp decline in accuracy of the
testing results, a modified algebraic reconstruction technique which improves accuracy by introducing biharmonic
spline interpolation is presented. In simulation, an error less than 3% in non-block situation is reached while an error less
than 8% in small-area-block situation is also obtained.
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