Digital phase-shifting point diffraction interferometer

Abstract

A digital phase-shifting (PS) point diffraction interferometer is demonstrated with a transmitting liquid crystal spatial light modulator. This novel wavefront sensor allows tunability in the choice of pinhole size and eliminates the need for mechanically moving parts to achieve PS. It is shown that this wavefront sensor is capable of sensing Zernike aberrations introduced with a deformable mirror. The results obtained are compared with those of a commercial Hartmann-Shack wavefront sensor.

Virtual pyramid wavefront sensor for phase unwrapping

“…4(a)) and no effects of noise were included while estimating the wrapped phase shown in Fig. 4(b) from the calculated interferograms [4,17]. The wavefronts reconstructed with the virtual PWS from the wrapped phase in Fig.…”

“…Here, the lens 'L' and the pyramidal phase T(x, y) are physically not present. The wrapped phase is obtained in a digital PS-PDI [17] and I pyr is evaluated using Eq. 1.…”

“…Here, the interferograms (I 1−3 ) in a digital PS PDI are obtained as described earlier [4,17]. Root-mean-square (RMS) of the residual wavefront is used to evaluate the quality of reconstruction [4].…”

“…Modulation plays an important role in controlling the dynamic range and sensitivity of the PWS [16] and its role in phase unwrapping is studied. The method is tested on noisy interferograms recorded experimentally with a CCD camera in a digital phase-shifting (PS) point diffraction interferometer (PDI) [4,17] by using a spatial light modulator to avoid mechanically moving components. The light used was a 632.8 nm He-Ne laser.…”

Reflective shearing point diffraction interferometer

“…An almost ideal spherical wavefront can be generated through a pinhole which can be regarded as reference wavefront instead of using reference sphere, and it can achieve an extremely high precision test of the wavefront theoretically. This is why point diffraction interferometer (PDI) [2] has been widely applied [3][4][5][6][7][8][9][10][11]. The main drawback of the PDI lies in the fact that it is difficult to extract the phase information from the PDI interferograms using the traditional methods.…”