Using high speed visualization to identify variations in the formation and distribution of plasmonic microbubbles
Mohammad Amer Allaf1, Koji Okamoto2, Takuto Owa3
1Nuclear Engineering and Engineering Physics, University of Wisconsin-Madison, Engineering Research Building, 1500 Engineering Drive, Madison, Wisconsin 53705, USA.
AIP Advances
|June 9, 2025
Summary
Gold nanoparticles (GNPs) heating with pulsed lasers (PLs) generates microbubbles, but aggregation and photomodification cause unpredictable variations. Optical pulling forces and dissolved gas release further influence microbubble formation and distribution.
Area of Science:
- Nanotechnology
- Photothermal Applications
- Microfluidics
Background:
- Plasmonic heating of gold nanoparticles (GNPs) with pulsed lasers (PLs) is crucial for microbubble generation in imaging, diagnostics, and microfluidics.
- Aggregation and photomodification of GNPs lead to inconsistencies in microbubble formation and distribution, especially in pool-like environments.
Purpose of the Study:
- To experimentally investigate microbubble generation by heating GNPs using pulsed lasers.
- To understand the influence of GNP size, concentration, and laser parameters on microbubble formation and distribution.
- To elucidate the roles of aggregation, photomodification, optical pulling forces, and dissolved gas release in the process.
Main Methods:
- Heating GNPs (532 nm, nanosecond PL) of various sizes and concentrations.
- Utilizing high-speed imaging at 20 kfps to capture microbubble dynamics.
- Analyzing bubble formation area (BFA) and distribution patterns.
Main Results:
- Observed unpredictable variations in BFA even with similar energy absorption.
- Large microbubbles formed at low energy absorption due to aggregation.
- Optical pulling forces caused GNP deposition on surfaces, leading to well-defined semi-circular bubbles (∼600 μm) within 50 μs.
- Microbubble formation was concentrated near backward-facing surfaces, indicating the role of optical pulling.
- Dissolved gas release influenced microbubble growth, particularly in aggregated samples.
- Prior laser pulses affected BFA through photomodification and aggregation, sometimes reducing BFA.
Conclusions:
- GNP aggregation, photomodification, optical pulling forces, and dissolved gas release are key factors influencing microbubble generation and distribution.
- Understanding these mechanisms is vital for improving the reliability and efficiency of photothermal applications.
- This study provides insights for better control over plasmonic bubble generation for scientific and technological advancements.
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