The most common approach to optically generate and manipulate bubbles in liquids involves temperature gradients induced by CW lasers. In this work, we present a method to accomplish both the generation of microbubbles and their 3D manipulation in ethanol through optothermal forces. These forces are triggered by light absorption from a nanosecond pulsed laser (λ = 532 nm) at silver nanoparticles photodeposited at the distal end of a multimode optical fiber. Light absorbed from each laser pulse quickly heats up the silver-ethanol interface beyond the ethanol critical-point (∼ 243 °C) before the heat diffuses through the liquid. Therefore, the liquid achieves a metastable state and owing to spontaneous nucleation converted to a vapor bubble attached to the optical fiber. The bubble grows with semi-spherical shape producing a counterjet in the final stage of the collapse. This jet reaches the hot nanoparticles vaporizing almost immediately and ejecting a microbubble. This microbubble-generation mechanism takes place with every laser pulse (10 kHz repetition rate) leading to the generation of a microbubbles stream. The microbubbles' velocities decrease as they move away from the optical fiber and eventually coalesce forming a larger bubble. The larger bubble is attracted to the optical fiber by the Marangoni force once it reaches a critical size while being continuously fed with each bubble of the microbubbles stream. The balance of the optothermal forces owing to the laser-pulse drives the 3D manipulation of the main bubble. A complete characterization of the trapping conditions is provided in this paper.
Manipulate nanoparticles with a laser-induced microbubble
A laser-induced microbubble refers to a bubble that is generated in a liquid solution by CW laser illumination to light absorptive materials. In this study, we use the gold nanoparticles solutions and gold nanoparticle film as the materials to absorb the heat under illumination. Heat transfer from the gold nanoparticles to surroundings induces a sharp increase in temperature, which results the generation of the microbubbles in the solutions. Therefore, the size and position of the surface bubble can be dynamically adjusted by changing the power and position of the laser spots. Convection currents around microbubble can make the gold nanoparticles pinned to the substrate surface, which can generate the Roman ring-shape structure. And then shine the CW laser of different power on the structure, the characteristics of the structure can be changed. These effects can be used for a wide variety of applications including micro/nano-particle manipulation, active microfluidic control, as well as cell stretching and sorting.
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- Award ID(s):
- 1761132
- NSF-PAR ID:
- 10210706
- Date Published:
- Journal Name:
- Optical Manipulation and Its Applications 2019
- Page Range / eLocation ID:
- JT4A.2
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1364/BODA.2019.JT4A.2
