LIPSS as well as hierarchical structures were generated by applying picosecond laser irradiation on a stainless steel-304 probe in a confinement liquid medium. Periodicity modification from high to low spatial surface frequency LIPSS was observed by modifying the pulse repetition rate from 1.3 to 402 kHz at a constant fluence. One of the outcomes reported in this study was the wettability analysis of the processed area which yielded significative changes on the contact angle between a water drop and the treated surface showing a wetting transition from hydrophilicity to hydrophobicity as an effect of the multiple impact pulses.
Silicon nanoparticles suspended in deionized water were obtained by the laser ablation of solids in liquids technique. A silicon wafer target was ablated with a Nd:YVO4 pico-second laser emitting at 1064 nm with 10 ps pulse width at a repetition rate of 402 kHz with an energy per pulse of 106 µJ. The effect of fluence changes in nanoparticle size and optical properties was studied. The fluence was varied from 2 to 6 J/cm2 by attenuating the beam by means of optical attenuators. Results show a strong relation between nanoparticles size and fluence values. Optical characterization gives bad gap values higher than that of bulk Si, indicating the existence of quantum confinement effects produced by size reduction of Si nanocrystals.
A laser shock wave is a mechanical high-pressure impulse with a duration of a few nanoseconds induced by a high power laser pulse. We performed wave pressure measurements in order to build and check mathematical models. They are used for wave applications in material science, health, and defense, to list a few. Piezoresistive methods have been shown to be highly sensitive, linear, and highly appropriate for practical implementation, compared with piezoelectric methods employed in shock wave pressure measurements. In this work, we develop a novel method to obtain the sensitivity of a piezoresistive measurement system. The results shows that it is possible to use a mechanical method to measure pressure of a laser induced shock wave in nanosecond range. Experimental pressure measurements are presented.
Strengthening techniques allows enhance metal physical properties. Laser shock peening (LSP) technique consist in a surface treatment which a high power laser pulse induces a compressive residual stress field through mechanical shock waves, increasing hardness, corrosion resistance, fatigue resistance. In comparison with the shot peening technique, LSP is a method that allows precision controlling the laser incidence on the surface under treatment increasing the surface quality in the surface under treatment. In this work, mechanical shock waves are induced in aluminum and measure using two different experimental approaches. First, using a PVDZ sensors and secondly, strain gauges are used. Experimental results are presented.
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.
Miguel Mora-González, Héctor Pérez Ladrón de Guevara, Jesús Muñoz-Maciel, Roger Chiu-Zarate, Francisco Casillas, Gilberto Gómez-Rosas, Francisco Peña-Lecona, Zuleima Montserrat Vázquez-Flores
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.
Laser shock processing (LSP) or laser shock peening has been proposed as a competitive alternative technology to
classical treatments for improving fatigue and wear resistance of metals. This process induces a compressive residual
stress field which increases fatigue crack initiation life and reduce fatigue crack growth rate. We present a configuration
and results in the LSP concept for metal surface treatments in underwater laser irradiation at 1064 nm with and without a
thin surface paint layer. A convergent lens is used to deliver 1, 2 J/cm2 with a 8 ns laser FWHM pulse produced by a 10
Hz, Q-switched Nd:YAG laser with a spot diameter of a 1,5 mm moving forward along the workpiece. A LSP
configuration with experimental results using a pulse density of 5000 pulses/cm2 in 6061-T6 aluminum samples are presented.
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 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 in diameter in 1040 steel samples are presented. Compressive residual stress distribution as a function of depth is assessed by the hole drilling method. High level compressive residual stresses are produced using 1064 nm wavelength. This method can be applied for surface treatment of final metal products.
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.
Although valuable experimental work has been performed in order to explore the optimum conditions of application of the treatments and to assess their capability to provide enhanced mechanical properties, there is little work done on the theoretical prediction of these optimum parameters. In the present paper, a model is presented to provide an estimation of the residual stresses and surface deformation in order to see the influence of the different parameters in the process. The influence of pulse duration, pulse pressure peak, spot radius, number of shots, overlapped shots and material properties are studied. The great influence of 3D deformation effects in the process is clearly shown as one of the most important limiting factors of the process traditionally neglected in previous literature. Additionally, from the experimental point of view, in the present paper a summary is provided of different results obtained from the most recent LSP experiments carried out by the authors along with some conclusions for the assessment of LSP technology as a profitable method for the extension of fatigue life in critical heavy duty components.
A new and simple method, the dynamic angle limited integrated scattering measurement technique is developed to examine light scattered from clean optically smooth reflective surfaces with random roughness. We present three new systems which have several advantages over the conventional angle resolved scattering (ARS) system. As scattered light is collected in a given solid angle, the measurement system does not require a detection unit with an extremely dynamic range. Unlike in the common ARS measurement system, in this method a linear movement is adopted to scan scattered light. This technique can be applied to the in-workshop inspection of the optical polishing process.
A push-broom imaging camera with time expansion, selected for its ability to generate images with high resolution and high radiometric signal, is described for accurate site-certification from space. The imaging system providing the high resolution imaging requires a sensor with an increased dwell time to generate a high radiometric signal. This may be accomplished by pointing the camera at each pixel for a longer interval of time than that available due to the sensor motion in the push-broom imaging configuration. This is referred to as the push-broom imaging with time expansion. The use of the camera with time expansion may be applicable to any remote sensing imaging problem that requires simultaneously high spatial resolution and a high level of radiometric signal. For surveying a Martian landing site, it is necessitated by the imaging from an autonomous orbiting sensor that's speed is determined by its orbit and the planet mass.
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