ResumenSe reporta la respuesta fotoacústica de un sensor piezoeléctrico que fue irradiado con pulsos láser de longitud de onda de 1064 nm y distinta energía emitidos por un láser Nd:YAG. La medida de la energía de los pulsos láser se hizo con un medidor, marca Newport modelo 1936-R con sensor piroeléctrico y las señales fotoacústicas con un osciloscopio Tektronix, modelo DPO3054 de 500 MHz. Experimentalmente se encontró una dependencia lineal entre la intensidad de la señal fotoacústica del sensor piezoeléctrico y la energía del pulso láser. La sensibilidad de la respuesta fotoacústica del sensor fue dependiente de la placa protectora. Para placas de aluminio y aluminio pintado de negro fueron (6.52 ± 0.06)mV /mJ y (51.2 ± 1.5)mV /mJ respectivamente. Se concluyó que este tipo de sensor piezoeléctrico es muy sensible a los cambios de energía de láseres pulsados de 1064 nm, su respuesta es directamente proporcional a la energía incidente, es apropiado para mediciones de energía de láseres pulsados en tiempo real y, no se ve afectado por ruidos acústicos ni condiciones de iluminación del laboratorio.
In this work we studied the microfibers of a textile (T-shirt) of the Chimú culture. This culture developed on the northern coast of Peru. To determine the raw material and structural quality of the microfibers, the results of the Chimú textile were compared with the corresponding results for the microfibers of cotton from the northern coast of Peru (native cotton). Scanning electron microscopy images revealed that the Chimú textile yarns are composed of a set of interwoven microfibers. Energy dispersive X-ray spectroscopy and pulsed laser-induced plasma spectroscopy techniques allowed the identification of characteristic cellulose atoms in the microfibers of Chimú textile and native cotton. Only for the Chimú textile, these spectroscopic techniques allowed the identification of atoms corresponding to natural dyes and powder residues. Attenuated total reflection Fourier transform infrared spectroscopy identified the same molecular bonds for the microfibers of Chimú textile and native cotton. For the microfibers of Chimú textile and native cotton, the X-ray diffractograms showed peaks characteristic of the cellulose Iβ polymorphism of of monoclinic P21 structure. The raw material of the Chimú textile is cotton and the microfibers of this material show significant structural stability.
In this work, the parameters for laser ablation cleaning of contaminants deposited by electrostatic attraction on cellulose acetate (OHP) sheet substrates and their analysis by measuring the transmittance of the irradiated surface as a function of the energy per pulse of an Nd:YAG laser were determined. The energy was controlled by the Q-switch delay time using wavelengths in the infrared region of 1064 nm and green visible light of 532 nm. A maximum of 10 laser pulses with a frequency of 1 Hz were used on the substrates with contaminants with 9 μm and 11 μm thickness. It was found that for damage-free laser cleaning of OHP film substrates it is convenient to use a wavelength of 1064 nm, with an energy per pulse of 33.36 mJ and using a maximum of 6 pulses. The advantages of pulsed laser radiation in the non-destructive cleaning of substrates with contaminants and the analysis of the substrate transmittance in the monitoring of lasermatter interaction processes were verified.
Se determinaron los umbrales de ablación láser de los metales cobre, oro y plata para la radiación láser de 1064 nm de un láser Nd:YAG de nanosegundos utilizándose la técnica fotoacústica pulsada para registrar las señales fotoacústicas producidas debido a la interacción del metal con los pulsos láser. Dichas señales se analizaron mediante correlación estándar y los cambios en la amplitud fotoacústica conforme aumento la fluencia láser. Los resultados indican que las señales fotoacústicas son muy sensibles a cambios físicos que experimenta una muestra solida debido a la interacción con pulsos láser, pudiendo diferenciarse claramente el cambio del régimen termoelástico al de ablación y por consiguiente el umbral de ablación. Los valores obtenidos para la fluencia umbral fueron: (1.71±0.08) J/cm2 para el cobre, (1.65±0.09) J/cm2 para el oro y (1.15±0.05) J/cm2 para la plata.
The effect of magnetic field of 0.3 T on the concentration, distribution of sizes in suspension and zeta potential of colloidal gold and colloidal silver nanoparticles, obtained by considering the pulsed laser ablation in double distilled water was studied. The magnetic field was transverse to the direction of incidence of the laser radiation and parallel to the surface of a submerged target. An Nd: YAG laser was used (1064 nm in wavelength, 10 ns in duration, repetition rate of 10 Hz and 37 mJ of energy) to ablate targets. The colloids were characterized by inductively coupled plasma optical emission spectroscopy, ultraviolet-visible spectroscopy, dynamic light scattering and zeta potential. Concentration analysis suggested that applying magnetic field of 0.3 T during nanoparticle synthesis leads to higher concentration. Applying magnetic field led to an eleven percent increase in the concentration of the colloid with gold nanoparticles and a five percent increase in the concentration of the colloidal silver nanoparticles. The absorption spectra suggested the presence of spherical nanoparticles. When analyzing the effect of the magnetic field on the hydrodynamic size distribution of the nanoparticles and the zeta potential of the colloids, no significant changes were evidenced. The magnetic confinement of the plasma induced by laser ablation caused changes in the characteristics of the colloids.
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