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We report a method for two-dimensional phase unwrapping based on the transport of intensity equation (TIE). Given a wrapped phase profile, we generate an auxiliary complex field and propagate it to small distances to simulate two intensity images on closely spaced planes. Using the longitudinal intensity derivative of the auxiliary field as an input, the TIE is solved by employing the regularized Fourier-transform-based approach. The resultant phase profile is automatically in the unwrapped form, as it has been obtained as a solution of a partial differential equation rather than as an argument of a complex-valued function. Our simulations and experimental results suggest that this approach is fast and accurate and provides a simple and practical solution for routine phase unwrapping tasks in interferometry and digital holography.

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The present paper reports on the microstructure, hardness, surface roughness, phases formed and corrosion behaviour of laser nitrided Ti -13Nb -13Zr biomedical alloy. Surface melting and nitriding of the alloy were carried out using a Nd : YAG laser in pulsed mode under dilute and pure nitrogen environments. Laser nitriding of the alloy resulted in a hardness of 1600 HV and 650 HV, respectively, for pure N 2 and dilute N 2 zAr environments. Cracks were not observed either on the surface or in the vertical cross-section of the samples nitrided in both environments. X-ray diffraction analysis of the sample nitrided in a pure nitrogen environment con rmed the formation of TiN, TiN 0 . 3 , alpha and beta phases along with ZrN. Quantitative analysis using electron probe microanalysis (EPMA) showed the enrichment of Zr and Ti in the dendrites. Corrosion resistance of the laser nitrided samples in a simulated body environment (Ringer's solution) was evaluated using the potentiodynamic polarisation method, and was found to be signicantly better for the laser nitrided conditions compared with the untreated alloy.

The criterion for ensuring formation of a through hole is an important aspect of laser drilling. Close observation of the process has indicated that drilling of the substrate is achieved in six successive microstages. The stages have been time resolved and the behaviour of laser induced plasma (LIP) during the microstages of drilling has been carefully examined. The LIP behaviour during the percussion laser drilling has been explained with the help of the contemporary understanding of plasma. This paper proposes a drilling completion criterion that is based on the behaviour of LIP during laser percussion drilling of SUPERNI 263A with a Nd-doped yttrium aluminium garnet laser. The completion of formation of a hole is marked by the momentarily increased luminescence of the plasma plume emanating from the laser beam exit side of the workpiece during drilling. The criterion has been experimentally verified. The criterion is versatile and can help in augmenting productivity during manufacturing.