The nonlinear optical properties of zinc oxide (ZnO) nanoparticles and tungsten doped zinc oxide (ZnO : WO3) nanoparticles are investigated by using the Z-scan technique. The ZnO was synthesized by sol–gel method. Also, the nanoparticles of ZnO : WO3 with the different molar ratio of tungsten were synthesized by sol–gel method. The result reveals that the nonlinear refractive index of ZnO is enhanced due to the addition of tungsten. Also, by adding molar ratio of tungsten doped in ZnO, the nonlinear refractive index is increased.
A wavefront sensor which takes advantage of the moire deflectometry has been constructed for measuring atmosphere
induced wavefront distortions. In this sensor a collimated laser beam propagates through turbulent
atmosphere, then a beam splitter splits it into two beams and the beams pass through a pair of moire deflectometers.
Directions of the grating's rulings are parallel in each moire deflectometer but are perpendicular in
the two beams. Using a suitable array of lenses and mirrors two sets of moire patterns are projected on a CCD
camera. A suitable spatial filter removes the unwanted frequencies. Recording the successive moire patterns by
the CCD camera and feeding them to a computer, allow temporal fluctuations of the laser beam wavefront phase
to be measured highly accurately. Displacements of the moire fringes in the recorded patterns correspond to the
fluctuations of two orthogonal components of the angle of arrival (AA) across the wavefront. The fluctuations
have been deduced in successive frames, and then evolution of the wavefront shape is determined. The implementation
of the technique is straightforward and it overcomes some of the technical difficulties of the Schlieren
and Shack-Hartmann techniques. The sensitivity of detection is adjustable by merely changing the distance
between two gratings in both moire deflectometers and relative grating ruling orientation. This overcomes the
deficiency of the Shack-Hartman sensors in that these require expensive retrofitting to change sensitivity. Besides,
in the moire deflectometry, the measurement is relatively insensitive to the alignment of the beam into
the device. Hence this setup has a very good potential for adaptive optics applications in astronomy. Since tilts
are measured in the Shack-Hartmann method at discrete locations, it cannot detect discontinuous steps in the
wavefront. By this method discontinuous steps in the wavefront are detectable, because AA fluctuations are
measured across the wavefront.