Optical Heating Controlled With a Thermoplasmonic Metasurface

We develop a photothermal technology to control optical heating of polymer and liquid crystal films through a refractory titanium nitride (TiN) metasurface. The metasurface represents an array of identical square-shaped TiN nanoantennas on a Si substrate. Upon CW laser illumination, a TiN nanoantenna experiences anomalous Joule heating at a plasmon resonance. A temperature rise provides a unique opportunity for locally probing phase transitions. In the case of heterogeneous PMMA thin films or polymeric blends, a controlled optical heating is needed to probe the glass transition temperature (Tg) of their constituents. Here, we model a controlled thermal response originating from the TiN nanoantenna under CW laser illumination by using FDTD/FEM methods.

Optical heating of doped semiconductor nanocylinders supporting quasi-BIC modes

In the recent years, semiconductor and dielectric nanophotonic structures attracted a lot of attention for their resonant optical properties finding applications in thermal tuning and optical heating. Exciting high quality optical modes of both electric and magnetic nature in nanoresonators of high-index materials, one can effectively enhance optical absorption in such structures. Another big advantage of semiconductor materials is the ability to finely control the level of optical losses in visible and near infrared (near-IR) range through varying the doping level. In this work, we show theoretically that by moderate carrier doping of silicon via donors from group V materials one can achieve effective heating of nanoresonators. We show that by tuning the doping level of crystalline silicon supporting high quality non-radiative modes based on quasi bound states in the continuum one can achieve strong heating in near-IR under continuous wave regime illumination. We believe that our finding will pave the way for an efficient semiconductor near-IR all-optical sensors and nanoheaters.

Hydrodynamic manipulation of nano-objects by optically induced thermo-osmotic flows

The manipulation of nano-objects at the microscale is of great technological significance to construct new functional materials, to manipulate tiny amounts of liquids, to reconfigure sensorial systems or to detect minute concentrations of analytes in medical screening. It is commonly approached by the generation of potential energy landscapes, for example, with optical fields or by using pressure driven microfluidics. Here we show that strong hydrodynamic boundary flows enable the trapping and manipulation of nano-objects near surfaces. These thermo-osmotic flows are induced by modulating the van der Waals interaction at a solid-liquid interface with optically generated temperature fields. We use a thin gold film on a glass substrate to provide localized but reconfigurable point-like optical heating. Convergent boundary flows with velocities of tens of micrometres per second are observed and substantiated by a quantitative physical model. The hydrodynamic forces acting on suspended nanoparticles and attractive van der Waals or depletion induced forces enable precise positioning and guiding of the nanoparticles. Fast multiplexing of flow fields further provides the means for parallel manipulation of many nano-objects and the generation of complex flow fields. Our findings have direct consequences for the field of plasmonic nano-tweezers as well as other thermo-plasmonic trapping schemes and pave the way for a general scheme of nanoscopic manipulation with boundary flows.

Real-Time Temperature Detection Via Quantum Dots for Photothermal Cellular Actuation

Plasmonic heating finds multiple applications in cell manipulation and stimulation, where heat generated by metal nanoparticles can be used to modify cell adhesion, control membrane currents, and suppress neuronal action potentials among others. Metal nanoparticles can also be easily integrated in artificial extracellular matrices to provide tunable, thermal cueing functionalities with nanometer spatial resolution. In this contribution, we present a platform enabling the combination of plasmonic heating with localized temperature sensing using quantum dots (QDs). Specifically, a functional nanocomposite material was designed with gold nanorods (AuNRs) and QDs incorporated in a cell-permissive hydrogel (e.g., collagen) as well as an optical set-up combining optical heating and temperature imaging, respectively. Specific area stimulation/readout can be realized through structured illumination using digital micromirror device (DMD) projection.

Dynamic Characterisation of Fibre-Optic Temperature Sensors for Physiological Monitoring

Fast, miniature temperature sensors are required for various biomedical applications. Fibre-optics are particularly suited to minimally invasive procedures, and many types of fibre-optic temperature sensors have been demonstrated. In applications where rapidly varying temperatures are present, a fast and well-known response time is important; however, in many cases, the dynamic behaviour of the sensor is not well-known. In this article, we investigate the dynamic response of a polymer-based interferometric temperature sensor, using both an experimental technique employing optical heating with a pulsed laser, and a computational heat transfer model based on the finite element method. Our results show that the sensor has a time constant on the order of milliseconds and a −6 dB bandwidth of up to 178 Hz, indicating its suitability for applications such as flow measurement by thermal techniques, photothermal spectroscopy, and monitoring of thermal treatments.