engleski

Laser drilling of metals in water: A model

Laser drilling of metals in water is essential method for synthesis of nanoparticles with adjustble size distribution and morphology given that there are many experimental parameters (energy, frequency, wavelength, pulse duration, number of pulses, radius of the pulse...) which determine characteristics of obtained nanoparticles. One of the most important quantites dependent on these parameters are volumes of craters from which concentration and diameter of produced nanoparticles may be determined. This paper shows that Gaussian profile of laser pulses used for drilling of craters, projects itself into the Gaussian profile of obtained crater depth vs. radius dependence. Comparison of volumes measured by optical microscopy and modeled ones show discrepancy in range ±10 % for Ag, ±15 % for Au and ±5 % for ZnO. Developed model states that there are 3 relevant points for full crater description given it has Gaussian profile: surface radius R_0, depth D and Gaussian waist ω which equals to radius at 1/e^2 depth. Comparison of volumes of craters measured by optical microscopy and modeled ones with 3 points gaussian fit show discrepancy in range ±10 % for Ag, ±15 % for ZnO and ±20 % for Au. Fluence profile of Gaussian laser pulses and areas of successive crater holes drilled with each pulse enables calculation of deposited energy in the crater where crucial parameters are ablation threshold of given metal for given wavelength and pulse duration and incident energy upon metal target. Obtained energies are bounded with lower limit which corresponds to minimal energy needed for heating, melting and evaporation of given volume of metal target and upper limit given as a maximal energy incident upon metal target for given number of pulses. Difference between upper limit energy and deposited energy equals to heat diffusion to the crater surroundings and difference between deposited energy and lower limit energy equals to heating of evaporated species up to plasma temperature and radiation of ignited plasma during laser ablation.

laser drilling of craters, Gaussian laser pulse, laser energy deposition, lower and upper energy limit

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