G. Gomez-Rosas

Phase recovery from a single interferogram with closed fringes by phase unwrapping

We describe a new algorithm for phase determination from a single interferogram with closed fringes based on an unwrapping procedure. Here we use bandpass filtering in the Fourier domain, obtaining two wrapped phases with sign changes corresponding to the orientation of the applied filters. An unwrapping scheme that corrects the sign ambiguities by comparing the local derivatives is then proposed. This can be done, assuming that the phase derivatives do not change abruptly among adjacent areas as occurs with smooth continuous phase maps. The proposed algorithm works fast and is robust against noise, as demonstrated in experimental and simulated data.

Induction of Engineered Residual Stresses Fields and Associate Surface Properties Modification by Short Pulse Laser Shock Processing

Laser shock processing (LSP) is consolidating as an effective technology for the improvement of metallic materials surface properties involving their fatigue life. The main acknowledged advantage of the LSP technique consists on its capability of inducing a relatively deep compression residual stresses field into metallic alloy pieces allowing an improved mechanical behaviour, explicitly the life improvement of the treated specimens against wear, crack growth and stress corrosion cracking. Progress accomplished by the authors in the line of practical development of the LSP technique at an experimental level, aiming its integral assessment from an interrelated theoretical and experimental point of view, is presented in this paper. Concretely, experimental results on the residual stress profiles and associated surface properties modification successfully reached in typical materials (especially Al and Ti alloys) under different LSP irradiation conditions are presented, a correlated analysis of the residual stress profiles obtained under different irradiation strategies and the evaluation of the corresponding induced surface properties as roughness and wear resistance being also presented. Through a coupled theoretical- experimental analysis the real possibilities of the LSP technique as a possible substitutive of related traditional surface modification techniques as, for example, shot peening.

Application of Laser Shock Processing System by Underwater Irradiation (1064 nm) in Metal Surface

Laser shock processing (LSP) is a technique for strengthening metals. This process induces a compressive residual stress field which increases fatigue crack initiation life, reduces fatigue crack growth rate and increases wear resistance of metals. We present a configuration and results in the LSP concept for metal surfaces treatments in underwater layer with constant thickness using laser irradiation at 1064 nm. A convergent lens is used to deliver 2, 5 J/cm2 in a 8 ns laser FWHM pulse produced by a Q‐switch Nd:YAG Laser. Experimental results using a pulse density of 5 000 pulses/cm2 and spots of 0, 8 mm to 1, 5 mm in diameter on AISI 1040 steel surfaces, Ti6A14V surfaces, 304 Stainless Steel surface and 6061‐T6 Aluminum surfaces are presented. A compressive residual stress distribution as a function of depth is assessed by the hole drilling method. High level compressive residual stresses are produced using a 1064 nm wavelength. This method can be applied for surface treatment of final metal products.

Discretization of quasi-sinusoidal diffraction gratings printed on acetates

The aim of this work is to propose the use of printed acetate sheets as quasi-sinusoidal diffraction gratings, as low-cost alternative gratings for application in non-invasive optical tests. Gratings were generated with Matlab® software and made with various models of laser printers. A study of the discretization effects that depend on the symmetry in the sample was included, gratings were placed in the entrance pupil of a positive lens (illuminated by a collimated plane wave) to observe their Fourier transforms. It was found that diffraction patterns of various types of semi-sinusoidal profiles were very close to that of sinusoidal gratings. Gradual change in the size of printed ink spots was observed in more detail through a magnification of 40x. Additionally, an atomic force microscope was used to measure the roughness average of the impressions as to observe the behavior of the ink on the acetate.

Scattering light measurement of optical surfaces using a new dynamic angle limited integrated scattering method

The dynamic angle limited integrated scattering (DALIS) method has been developed to examine optically smooth reflective surfaces with well-defined form. The DALIS system shows advantages over the conventional angle-resolved scattering. We propose a new configuration and results in the DALIS method by using a spherical mirror as a collecting element of the scattered light from the surface of a sample under test. Furthermore, the proposed method improves the detection of the scattered light and is suitable to be applied in workshop inspection during optical polishing processes.

Laser shock processing system by underwater irradiation (532 nm) in metal surface

Laser shock processing (LSP) has been proposed as a competitive alternative technology to classical treatments for improving fatigue and wear resistance of metals. We present a configuration and results in the LSP concept for metal surfaces treatments in underwater laser irradiation at 535 nm. A convergent lens is used to deliver 0.9 J/cm2 in an 8 ns laser FWHM pulse produced by 10 Hz Q-switched Nd:YAG Laser with spots of a 1.5 mm in diameter moving forward along the workpiece. A LSP configuration with experimental results using a pulse density of 2 500 pulses/cm2 and 5 000 pulses/cm2 in 6061-T6 aluminum samples are presented by 532 nm. High level of compressive residual stresses are produced (600 MPa-750 MPa) with a depth of 1.2 mm. It has been shown that surface residual stress level is comparable to that achieved by conventional shot peening, but with greater depths. This method can be applied to surface treatment of final metal products.