The structure for thermal tweezers with laser pulse treatment. A thin metal film of thickness is deposited onto a glass slab of thickness . Two coherent laser pulses are incident at onto the film surface, creating an interference pattern. Optical absorption of the electromagnetic energy results in periodic heating of the film. Nanoparticles or adatoms placed onto the surface of the metal film diffuse predominantly from hot to cold regions due to surface thermophoresis (Ref. 12). The particles are regarded nonabsorbing and noninteracting with the incident radiation.
Two examples of the temperature distributions on the nickel film with , (pulse wavelength ) and (Refs. 17 and 18) on the glass substrate with and (Ref. 18) for the two different pulse lengths and energies: (a) and , (b) and . The solid and dotted curves correspond to the heating process during the laser pulse, while the dashed curves represent the cooling process. The dotted curves correspond to the middle of the Gaussian pulse. The thick solid curve corresponds to the maximal temperature on the surface of the film. If the time at the middle of the pulse (the dotted curves), then the respective times for all the curves are: (a) , , 0, 1, 2.5, and 7.5 ns; and (b) , 0, 0.1, 0.2, 0.5, and 1.0 ns.
The time dependencies of the maximum and minimum temperatures on the surface of the film and the difference between them . The dependencies in subplots (a) and (b) correspond to the temperature distributions shown in Figs. 2(a) and 2(b), respectively.
The -dependencies of the probability density function within two periods of the temperature modulation on the surface as a result of laser pulse treatment using three sequential pulse series: (1) and (pulses from 1 to 50), (2) and (pulses from 51 to 150), and (3) and (pulses from 151 to 550). The mass of the particles atomic units, , and (Refs. 12 and 20); the other structural parameters are the same as for Figs. 2 and 3. The dashed, dotted, and solid curves correspond to 10 pulses, 150 pulses, and 550 pulses, respectively.
The dependencies of the probability density function at a minimum (a) and maximum (b) of surface temperature on number of pulses during the three sequential laser pulse series with the parameters described in the caption for Fig. 4. Curves 1, 2, and 3 correspond to the first, second, and third pulse series, respectively. The horizontal dashed lines represent the asymptotic values of probability densities at the minimum (a) and maximum (b) surface temperature for the three considered pulse regimes. The dotted curve in (a) is the extension of the exponential dependence used to fit the numerical data points for the third pulse series.
The -dependencies of the probability density functions illustrating the superresolution technique. The dashed curve is identical to the solid curve in Fig. 4, and represents the initial particle distribution (e.g., achieved previously by application of thermal tweezers as for Fig. 4). The temperature modulation (laser interference) pattern is phase shifted by , compared to what it was in Fig. 4, so that the maximum temperature coincides with the initial maximum concentration on the surface (dashed curve). The dotted and solid curve show the particle redistribution as a result of 200 pulses and 600 pulses, respectively, with and (these are the same as for pulses from the third pulse series used for Figs. 4 and 5).
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