arXiv subjects

P. Malara

Publications and source records attributed to P. Malara.

3 recordsLinked to original sources

arXiv2025

High-velocity optothermal whirlpool actuation at the air-water interface

In a meniscus lifted above a free water surface by an optical fiber delivering near infrared radiation, the upper confinement of the heated buoyant liquid amplifies the surface temperature gradient, driving particularly strong thermocapillary effects. When the temperature gradient within the meniscus becomes very large, the stationary convection flow destabilizes in a periodic pattern of surface hydrothermal waves. We show that these light fueled waves can be controlled to a large extent by acting on the system parameters, and harnessed to propel buoyant macroparticles along stable closed trajectories at exceptionally high speeds. With 20 mW of input power at 1550 nm, we observe fast linear oscillations of 0.1 to 1 mm particles with peak velocities up to 2 cm/s and a whirlpool-like stable orbital motion with rotation rate up to 600 rpm, the largest reported so far for optothermal actuation. These findings establish a new efficient method for contactless actuation on liquid surfaces with direct application in microfluidics and in the realization of efficient light powered micromotors. At the same time, the proposed fiber meniscus configuration provides a simple and adaptable platform for studying optothermal fluid instabilities and for generating and controlling surface thermocapillary waves.

physics.flu-dyn↗

arXiv2016

Super-Resonant Intracavity Coherent Absorption

The capability of optical resonators to extend the effective radiation-matter interaction length originates from a multipass effect, hence is intrinsically limited by the resonator quality factor. Here, we show that this constraint can be overcome by combining the concepts of resonant interaction and coherent perfect absorption. We demonstrate and investigate super-resonant coherent absorption in a coupled Fabry-Perot-ring cavity structure. At the FP resonant wavelengths, the described phenomenon gives rise to split modes with a nearly-transparent peak and a peak whose transmission is exceptionally sensitive to the intracavity loss. For small losses, the effective interaction pathlength of these modes is proportional respectively to the ratio and the product of the individual finesse coefficients of the two resonators. The results presented extend the conventional definition of resonant absorption and point to a way of circumventing the technological limitations of ultrahigh-quality resonators in spectroscopy and optical sensing schemes

physics.optics↗

arXiv2013

Enhanced sensing with quasi-degenerate mode in fiber Bragg gratings ring cavities

In this paper, we report the model and the experimental demonstration of a new optical resonator formed by inserting a Fiber Bragg Grating (FBG) in a closed fiber loop. The spectral characteristics of the ring depend on the reflectivity of the FBG. When the FBG reflectivity tends to zero, the overall resonant system exhibits the usual degenerate mode conditions. On the other hand, when the reflection coefficient FBG is not vanishing, the spectral features of the resonator display split resonant modes associated to the degeneracy removal of two counterpropagating modes that resonate within the cavity. The splitting magnitude is maximal in the region of maximum reflectivity of the FBG. Moreover, it varies by acting on the FBG physical parameters (e.g. strain, temperature, group index). By considering the spectral region where the splitting magnitude variation is almost maximal, i.e. quasi degenerate mode condition, we prove that the device can be used also as a slow light sensor by monitoring the power change associated with the applied strain showing, in this case, a sensitivity of 3.6x10^(6)x eps^(-1). To the best of our knowledge, this represents a factor 20 improvement over the best slow-light FBG sensors.

physics.optics↗