Optothermal Effect Research Articles

Brownian colloids in optothermal field: An experimental perspective

Colloidal matter undergoing Brownian motion serves as a model system to study various physical phenomena. Understanding the effect of external perturbation on the assembly and dynamics of “Brownian colloids” has emerged as a relevant research issue in soft matter and biological physics. Optical perturbation in the form of photonic forces and torques has added impetus to this exploration. In recent years, optothermal effects arising due to optical excitation of mesoscale matter have expanded the toolbox of light–colloidal matter interactions. In this perspective, we present an experimental viewpoint on some of the developments related to the assembly and dynamics of Brownian colloids driven by the optothermal field. Furthermore, we discuss some interesting prospects on driven colloidal matter that can have implications on soft matter physics and soft photonics.

Optical Actuation of Nanoparticle-Loaded Liquid-Liquid Interfaces for Active Photonics.

Liquid-liquid interfaces hold the potential to serve as versatile platforms for dynamic processes, due to their inherent fluidity and capacity to accommodate surface-active materials. This study explores laser-driven actuation of liquid-liquid interfaces with and without loading of gold nanoparticles and further exploits the laser-actuated interfaces with nanoparticles for tunable photonics. Upon laser exposure, gold nanoparticles were rearranged along the interface, enabling the reconfigurable, small-aperture modulation of light transmission and the tunable lensing effect. Adapting the principles of optical and optothermal tweezers, we interpreted the underlying mechanisms of actuation and modulation as a synergy of optomechanical and optothermal effects. Our findings provide an analytical framework for understanding microscopic interfacial behaviors, contributing to potential applications in tunable photonics and interfacial material engineering.

Probing Temperature-Induced Plasmonic Nonlinearity: Unveiling Opto-Thermal Effects on Light Absorption and Near-Field Enhancement.

Precise measurement and control of local heating in plasmonic nanostructures are vital for diverse nanophotonic devices. Despite significant efforts, challenges in understanding temperature-induced plasmonic nonlinearity persist, particularly in light absorption and near-field enhancement due to the absence of suitable measurement techniques. This study presents an approach allowing simultaneous measurements of light absorption and near-field enhancement through angle-resolved near-field scanning optical microscopy with iterative opto-thermal analysis. We revealed gold thin films exhibit sublinear nonlinearity in near-field enhancement due to nonlinear opto-thermal effects, while light absorption shows both sublinear and superlinear behaviors at varying thicknesses. These observations align with predictions from a simple harmonic oscillation model, in which changes in damping parameters affect light absorption and field enhancement differently. The sensitivity of our method was experimentally examined by measuring the opto-thermal responses of three-dimensional nanostructure arrays. Our findings have direct implications for advancing plasmonic applications, including photocatalysis, photovoltaics, photothermal effects, and surface-enhanced Raman spectroscopy.

All-in-one, all-optical logic gates using liquid metal plasmon nonlinearity

Electronic processors are reaching the physical speed ceiling that heralds the era of optical processors. Multifunctional all-optical logic gates (AOLGs) of massively parallel processing are of great importance for large-scale integrated optical processors with speed far in excess of electronics, while are rather challenging due to limited operation bandwidth and multifunctional integration complexity. Here we for the first time experimentally demonstrate a reconfigurable all-in-one broadband AOLG that achieves nine fundamental Boolean logics in a single configuration, enabled by ultrabroadband (400–4000 nm) plasmon-enhanced thermo-optical nonlinearity (TONL) of liquid-metal Galinstan nanodroplet assemblies (GNAs). Due to the unique heterogeneity (broad-range geometry sizes, morphology, assembly profiles), the prepared GNAs exhibit broadband plasmonic opto-thermal effects (hybridization, local heating, energy transfer, etc.), resulting in a huge nonlinear refractive index under the order of 10−4−10−5 within visual-infrared range. Furthermore, a generalized control-signal light route is proposed for the dynamic TONL modulation of reversible spatial-phase shift, based on which nine logic functions are reconfigurable in one single AOLG configuration. Our work will provide a powerful strategy on large-bandwidth all-optical circuits for high-density data processing in the future.

Gilded vaterite optothermal transport in a bubble

Laser beams, capable of controlling the mechanical motion of micron-scale objects, can serve as a tool, enabling investigations of numerous interaction scenarios under full control. Beyond pure electromagnetic interactions, giving rise to conventional gradient forces and radiation pressure, environment-induced thermal effects can play a role and, in certain cases, govern the dynamics. Here we explore a thermocapillary Marangoni effect, which is responsible for creating long-range few hundreds of nano-Newton forces, acting on a bubble around a ‘gilded vaterite’ nanoparticle. Decorating calcium carbonate spherulite (the vaterite) with gold nanoseeds allows tuning its optical absorption and, as a result, controlling its temperature in a solution. We demonstrate that keeping a balance between electromagnetic and thermal interactions allows creating of a stable micron-scale bubble around the particle and maintaining its size over time. The bubbles are shown to remain stable over minutes even after the light source is switched off. The bubbles were shown to swim toward a laser focus for over 400-µm distances across the sample. Optothermal effects, allowing for efficient transport, stable bubble creation, and particle–fluid interaction control, can grant nano-engineered drug delivery capsules with additional functions toward a theragnostic paradigm shift.

Multiphysics Modeling of Plasmon-Enhanced All-Optical Helicity-Dependent Switching.

In this work, we propose a multiphysics approach to simulate all-optical helicity-dependent switching induced by the local hot spots of plasmonic nanostructures. Due to the plasmonic resonance of an array of gold nanodisks, strong electromagnetic fields are generated within the magnetic recording media underneath the gold nanodisks. We construct a multiphysics framework considering the opto-magnetic and opto-thermal effects, and then model the magnetization switching using the Monte Carlo method. Our approach bridges the gap between plasmonic nanostructure design and magnetization switching modeling, allowing for the simulation of helicity-dependent, nanoscale magnetization switching in the presence of localized surface plasmons.

A flexible strain sensor based on MXene/AgNW composite film with extremely high sensitivity and low strain range for real-time health monitoring and thermal management

Flexible electronic devices have received increasing attention due to their potential applications in wearable human motion and healthcare monitoring and thermal management. Nevertheless, flexible electronic devices for more precise health monitoring of human physiological movement under low strain are still a pressing issue to solve. Herein, a wearable flexible strain sensor with a three-dimensional (3D) conductive network is developed for healthcare monitoring and thermal management by embedding silver nanowires (AgNWs) and Ti3C2T x MXene composite films into a polydimethylsiloxane matrix. The sensor can be utilized for human health monitoring, pulse detection at the wrist, and breathing monitoring of human physiological movement due to its low strain detection capacity (0.05% strain) and high sensitivity (gauge factor up to 9472). The primary detection range of the sensor is 0%–1% of tiny strains. Moreover, the exceptional electric heating and optothermal effect supported by the AgNWs and MXene protects human health in extremely cold environments. The MXene/AgNW strain sensor with high sensitivity under low strain has great potential for more precise health monitoring of human physiological movements and thermal management.

Characterization of laser-induced optothermal effect in magnetic fluids based on a coreless-fiber-coupled microcavity Mach-Zehnder interferometric sensor

We present an integrated coreless-fiber-coupled microcavity Mach-Zehnder interferometric sensor to investigate the optothermal effect of magnetic fluids in the near-infrared wavelength region. The Brownian motion of magnetic nanoparticles and solvent molecules intensifies along with the change of medium refractive index under 473 nm laser illumination, and consequently the interference wavelengths are sensitive to the applied laser power. The maximum wavelength tuning sensitivity is up to 4.7475 nm/(mW/mm2) at a microcavity length of 262.26 µm. Based on interferometric spectral analysis, the refractive index sensitivities of the magnetic fluids are found to be about −3.0909 × 10-4 RIU/(mW/mm2) and −3.3319 × 10-4 RIU/(mW/mm2) for the laser power increase and decrease processes, respectively. The slight difference between the refractive index sensitivities could be attributed to the accumulation of laser energy and Sorét effect. The work presented in this paper provides important references for understanding the optothermal mechanism of magnetic fluids and the design of magnetic-fluids-functionalized laser-controlled photonic devices.

An opto-thermal approach for assembling yeast cells by laser heating of a trapped light absorbing particle.

Cell assembly has important applications in biomedical research, which can be achieved with laser-heating induced thermal convective flow. In this paper, an opto-thermal approach is developed to assemble the yeast cells dispersed in solution. At first, polystyrene (PS) microbeads are used instead of cells to explore the method of microparticle assembly. The PS microbeads and light absorbing particles (APs) are dispersed in solution and form a binary mixture system. Optical tweezers are used to trap an AP at the substrate glass of the sample cell. Due to the optothermal effect, the trapped AP is heated and a thermal gradient is generated, which induces a thermal convective flow. The convective flow drives the microbeads moving toward and assembling around the trapped AP. Then, the method is used to assemble the yeast cells. The results show that the initial concentration ratio of yeast cells to APs affects the eventual assembly pattern. The binary microparticles with different initial concentration ratios assemble into aggregates with different area ratios. The experiment and simulation results show that the dominant factor in the area ratio of yeast cells in the binary aggregate is the velocity ratio of the yeast cells to the APs. Our work provides an approach to assemble the cells, which has a potential application in the analysis of microbes.

Integration of in situ Fenton-like self-cleaning and photothermal membrane distillation for wastewater treatment via Co-MoS2/CNT catalytic membrane

Intensive energy dependence and membrane fouling are the inherent limitations of membrane distillation (MD) process for the application. Solar energy is promising sustainable energy for both alleviating the energy shortage and activating the Fenton-like reaction for various pollutants degradation. By in situ integrating Fenton-like and photothermal MD processes, the restriction of energy dependence and membrane fouling on the MD process might be effectively liberated. In this study, Co-MoS2/CNT was introduced to PTFE membrane modification through vacuum filtration, which simultaneously endowed the membrane with optothermal effect and Fenton-like activation abilities. The membrane was evaluated in a dye wastewater treatment under the irradiation of 1 kW/m2 light density. Results showed that the degradation degree of RhB can reach 80 % within 1 h on the feed side, while the permeate flux maintains at 2.43 kg/(m2·h) with an initial feed temperature of 35 °C. In addition, the flux of the Co-MoS2/CNT/PTFE membrane can be maintained above 95 % after three fouling-cleaning cycles, indicating that the modified membrane has a good self-cleaning performance. This work provides a low carbon option which improving mass transfer effect and fouling control ability for dye wastewater treatment by MD using solar energy.

Optothermal effect on frequency measurement of suspended graphene mechanical resonator

In this work, the influence of the optothermal effect on mechanical resonance properties of a graphene mechanical resonator is investigated based on an optical fiber-based Fabry–Perot cavity. When optical power rise, the resonance frequency blueshifts in an exponential relationship, whereas amplitude rises in a linear relationship. The tuning range of resonance frequency can reach up to 9.95 % with a total optical power variation of 2.00 mW. The resonance frequency variation tuned by the optothermal effect shows good stability and repeatability. The result is helpful for deviation analysis in graphene mechanical resonators measurement employing optical actuation and detection methods. It can be further used to design graphene mechanical resonator-based tunable devices.

Pulsed thermography with laser beam homogenizing for thickness prediction of thin semi-transparent thermal barrier coatings

A pulsed thermography system with laser beam homogenizing is developed to measure the thickness of thermal barrier coatings (TBCs) by numerical fitting. A simplified model is proposed to avoid the complexity of deriving an analytical solution of thermal diffusion in TBC systems that include a thin semi-transparent top coating. A characteristic parameter is identified that captures the system response to fast heating by a short laser pulse and to optothermal effects due to volume heating, bulk emission and multiple reflections in the thin coating. It is demonstrated that small thickness changes can be measured when the unpainted ultra-thin TBC is thermally excited using short laser pulses with flat-top spatial profile. Experimental results show that the proposed laser thermography reconstruction method is fast and reliable when using laser beam shaping with a homogenizer.

The role of temperature-induced effects generated by plasmonic nanostructures on particle delivery and manipulation: a review

Abstract Plasmonic optical tweezers that stem from the need to trap and manipulate ever smaller particles using non-invasive optical forces, have made significant contributions to precise particle motion control at the nanoscale. In addition to the optical forces, other effects have been explored for particle manipulation. For instance, the plasmonic heat delivery mechanism generates micro- and nanoscale optothermal hydrodynamic effects, such as natural fluid convection, Marangoni fluid convection and thermophoretic effects that influence the motion of a wide range of particles from dielectric to biomolecules. In this review, a discussion of optothermal effects generated by heated plasmonic nanostructures is presented with a specific focus on applications to optical trapping and particle manipulation. It provides a discussion on the existing challenges of optothermal mechanisms generated by plasmonic optical tweezers and comments on their future opportunities in life sciences.

Taper-assisted coupling between two optical cavities at exceptional point and bound state in the continuum

Long-distance coupling between two optical cavities is enabled through a taper fiber. Phase shift and loss induced by the taper lead to complex coupling strength and hence observation of various distinctive coupling conditions like exceptional points, bound state in the continuum, and dissipative coupling with optothermal effect. Large tunability of coupling conditions is demonstrated via controlling the translation stage, as manifested in the transmission spectrum. Theoretical prediction and simulation coincide well with experimental measurement. Lastly, we propose to advance the role of taper for application in taper-based sensing and optomechanics.

Mapping the Stability and Dynamics of Optically Injected Dual State Quantum Dot Lasers

Optical injection is a key nonlinear laser configuration both for applications and fundamental studies. An important figure for understanding the optically injected laser system is the two parameter stability mapping of the dynamics found by examining the output of the injected laser under different combinations of the injection strength and detuning. We experimentally and theoretically generate this map for an optically injected quantum dot laser, biased to emit from the first excited state and optically injected near the ground state. Regions of different dynamical behaviours including phase-locking, excitability, and bursting regimes are identified. At the negatively detuned locking boundary, ground state dropouts and excited state pulses are observed near a hysteresis cycle for low injection strengths. Higher injection strengths reveal μs duration square wave trains where the intensities of the ground state and excited state operate in antiphase. A narrow region of extremely slow oscillations with periods of several tens of milliseconds is observed at the positively detuned boundary. Two competing optothermal couplings are introduced and are shown to reproduce the experimental results extremely well. In fact, the dynamics of the system are dominated by these optothermal effects and their interplay is central to reproducing detailed features of the stability map.

Optothermal Effect on Frequency Measurement of Suspended Graphene Mechanical Resonator

Optothermal Effect on Frequency Measurement of Suspended Graphene Mechanical Resonator

Reflective Meta-Films with Anti-Damage Property via Field Distribution Manipulation

The reflective optical multi-films with high damage thresholds are widely used in intense-light systems. Metasurfaces, which can manipulate light peculiarly, give a new approach to achieve highly reflective films by a single-layer configuration. In this study, reflective metasurfaces, composed of silicon nanoholes, are numerically investigated to achieve high damage thresholds. These nanoholes can confine the strongest electric field into the air zone, and, subsequently, the in-air electric field does not interact directly with silicon, attenuating the optothermal effect that causes damage. Firstly, the geometrical dependencies of silicon nanoholes’ reflectance and field distribution are investigated. Then, the excitation states of electric/magnetic dipoles in nanostructures are analyzed to explain the electromagnetic mechanism. Furthermore, the reflection dependences of the nanostructures on wavelength and incident angle are investigated. Finally, for a typical reflective meta-film, some optothermal simulations are conducted, in which a maximum laser density of 0.27 W/µm2 can be handled. The study provides an approach to improve the laser damage threshold of reflective nanofilms, which can be exploited in many intense-light applications.

A NIR laser induced self-healing PDMS/Gold nanoparticles conductive elastomer for wearable sensor

Self-healing conductive elastomers have been widely used in smart electronic devices, such as wearable sensors. However, nano fillers hinder the flow of polymer segments, which make the development of conductive elastomer with rapid repair and high ductility a challenge. In this work, thioctic acid (TA) was grafted onto amino-modified polysiloxane (PDMS-NH2) by dehydration condensation of amino group and carboxyl group. By introducing gold nanoparticles, a dynamic network based on S-Au interaction was constructed. The dynamic gold cross-linking could effectively dissipate the energy exerted by external force and improve the extensibility of conductive elastomer. In addition, S-Au interaction had a good optothermal effect, so that the elastomer rapidly healed under NIR irradiation, and the repair efficiency reached 92%. We further evaluated the performance of the conductive elastomer as a strain sensor. The sample could accurately monitor the bending of human joints and small muscle state changes. This kind of self-healable conductive elastomer based on dynamic S-Au interaction has great potential in the fields of interpersonal interaction and health monitoring.

Amidoximated wooden solar evaporator for high-efficiency nuclear wastewater treatment.

The efficient removal of uranium (VI) (UO22+) is of great significance to the ecological environment. However, there is still a lack of efficient adsorption materials to remove UO22+ in wastewater economically. Because natural basswood has high porosity, natural hydrophilicity, and abundant surface functional groups, wood as a support material has a good application prospect in water treatment. In the present work, the amidoxime functional group (AO) is grafted to the hydroxyl group of the wood fiber (AO-wood). A carbon layer is formed on the surface of the basswood by heating, and some Ag nanoparticles with good optothermal effect are added to the wood tunnel (Ag-C-AO-wood). Ag-C-AO-wood is used for efficient wastewater treatment under light conditions. The adsorption kinetic of Ag-C-AO-wood is 4.6 h under one irradiation, which is 7 times faster than AO-wood. It has approached or even surpassed some traditional carbon materials with stirring. This method is expected to break the traditional stirring method. Ag-C-AO-wood can not only remove uranium up to 82% but also have a good removal efficiency (27%) on iodide ions. More importantly, due to basswood characteristics, it is possible to large-scale preparation and explore its potential application value in wastewater.

Meta-Deflectors Made of Dielectric Nanohole Arrays with Anti-Damage Potential

In intense-light systems, the traditional discrete optical components lead to high complexity and high cost. Metasurfaces, which have received increasing attention due to the ability to locally manipulate the amplitude, phase, and polarization of light, are promising for addressing this issue. In the study, a metasurface-based reflective deflector is investigated which is composed of silicon nanohole arrays that confine the strongest electric field in the air zone. Subsequently, the in-air electric field does not interact with the silicon material directly, attenuating the optothermal effect that causes laser damage. The highest reflectance of nanoholes can be above 99% while the strongest electric fields are tuned into the air zone. One presentative deflector is designed based on these nanoholes with in-air-hole field confinement and anti-damage potential. The 1st order of the meta-deflector has the highest reflectance of 55.74%, and the reflectance sum of all the orders of the meta-deflector is 92.38%. The optothermal simulations show that the meta-deflector can theoretically handle a maximum laser density of 0.24 W/µm2. The study provides an approach to improving the anti-damage property of the reflective phase-control metasurfaces for intense-light systems, which can be exploited in many applications, such as laser scalpels, laser cutting devices, etc.