... and photothermal effects

[22] Laser & Photon. Rev. 7, 171 (2013)
[38] Thermoplasmonics, Cambridge University Press, G. Baffou (2017)

Under illumination at their plasmonic resonances wavelength, gold nanoparticles behave at ideal and efficient nanosources of heat, remotely controllable by light. The concept is at the basis of a research field called Thermoplasmonics [22,38].

Such tools enable the investigation of thermally induced processes at the nano and micro scales. And as any field of science feature thermally induced processes, the range of application of thermoplasmonics is limitless.

Following this idea, we are carrying out research in thermoplasmonics applied to physics, chemistry and cell biology, in order to elucidate new fundamental processes and imagine new applications of nanosciences.

... and quantitative phase imaging

Since 2011, we are extensively using a quantitative phase imaging technique called Quadriwave Lateral Shearing Interferometry (QLSI). This techniques enables the imaging of the intensity and phase of a light beam from the acquisition of a single interferogram image, with high spatial resolution (diffraction limited) and high wavefront sensitivity (wavefront distortion of lass than a nm).

We have shown that QLSI appears as a powerful tool in nanophotonics, as it enables:

[17] ACS Nano 6, 2452 (2012)

• temperature microscopy in thermoplasmonics systems [17],

[39] ACS Photon. 4, 3130-3139 (2017)

• optical characterization of 2D materials (mapping of the optical complex conductivity) [39],

[46] Optica accepted (2020)

• full characterization of the optical properties of nanoparticles from a single interferogram image (complex optical polarizability, and all the optical cross sections [46].

... and theory

[27] Nanoscale 6, 8984 (2014)
[43] Sci. Rep. 9, 4644 (2019)
[33] J. Phys. Chem. C 119, 25518 (2015)
[36] Sci. Rep. 6, 38647 (2016)
[14] Phys. Rev. B 82, 165424 (2010)
[15] Phys. Rev. B 84, 035415 (2011)
[28] Phys. Rev. B 90, 035439 (2014)
[24] ACS Nano 7, 6478-6488 (2013)

Along with the experimental research axes listed above, we also often focus on more fundamental researcher by publishing purely theoretical or numerical articles in nanophotonics and plasmonics, e.g. in nanoscale temperature shaping [27,43], search for more efficient plasmonic materials [33,36], dyadic Green's formalism [14], DDA and BEM for computation in plasmonics and thermoplasmonics [36], pulsed [15] and harmonic [28] optical heating of nanoparticles, photothermal collective effects [24], etc.

Living cells and light

We are setting up an new research activity looking at the sensitivity of different types of living cells in culture (including neurons) to light.

Living cells and heat

We are developing a research activity aimed to promote the concept of single cell thermal biology, which consists in heating living cells in culture individually. For this purpose, we culture living cells on a gold nanoparticle layer that acts as a heating layer under illumination. The main benefits of such an approach, compared to common overall heating of the whole sample, is to achieve fast dynamics (we do not suffer from any heating inertia) and subcellular heating.

[29] Nature Methods 11, 899 (2014)
[31] Nature Methods 12, 803 (2015)

In such studies, we have developed a label-free temperature microscopy technique based on QLSI [29,31], which does not suffer from possible artifacts associated with fluorescence-based techniques.

[41] Small 14, 1801910 (2018)

So far this approach enabled us to control cell migration and study heat shock response dynamics [41].

Quadriwave lateral shearing interferometry is a quantitative phase imaging technique (also called wavefront sensing technique), based on the use of a simple camera, which enables the mapping of the intensity and phase of a light beam, with unprecedented spatial resolution (diffraction limited) and sensitivity (0.3 nm/√Hz). Plugged onto a microscope, this technique can be used to characterized micro and nanoobjects via the wavefront distortion they induce on the illumination beam of the microscope.

... for temperature microscopy in plasmonics

[17] ACS Nano 6, 2452 (2012)

When immersed in a liquid, light-heated gold nanoparticles can easily generate a decrease of the refractive index of the liquid, leading to a thermal lens effects than can be probed by QLSI. The processing of this measured wavefront distortion can yield to an estimation of the temperature increase in the sample [17]. This technique, called TIQSI, for temperature imaging using QLSI, has the enormous benefit to be label-free and enabled us to carry out research in photothermal processes at small scales in physics, chemistry and cell biology, e.g.:

[20] ACS Nano 6, 7227 (2012)

• the control of living cell migration [20],

[21] Phys. Rev. B 86, 165417 (2012)

• quantitative absorption spectroscopy of nano-objects [21],

[24] ACS Nano 7, 6478-6488 (2013)

• the study of collective photothermal effects in thermoplasmonics [24],

[25] J. Phys. Chem. C 118, 4890 (2014)

• the study of bubble formation and water superheating [25],

[27] Nanoscale 6, 8984-8989 (2014)

• deterministic temperature shaping using plasmonic nanoparticle assemblies [27],

[30] ACS Nano 9, 5551-5558 (2015)

• the quantitative study of the photothermal properties of metallic nanowire networks [30],

[35] ACS Omega 1, 2-8 (2016)

• the demonstration of the concept of light-Assisted solvothermal chemistry using plasmonic nanoparticles [35],

[41] Small 14, 1801910 (2018)

• Photothermal control of heat-shock protein expression at the single cell level [41],

[43] Sci. Rep. 9, 4644 (2019)

• microscale temperature shaping using spatial light modulation on gold nanoparticles [43].

... for 2D-material optical characterization

[39] ACS Photon. 4, 3130-3139 (2017)

More recently, we imaged 2D materials, such as graphene and MoS₂ using QLSI and demonstrated that intensity and phase images could be jointly processed to retrieve all the optical properties of the 2D materials, i.e., the complex optical conductivity or polarizability [39].

... for nanoparticle optical characterization

[46] Optica, just accepted (2020)

Following the same principle, we also demonstrated that QLSI could fully quantify the optical properties of nanoparticles, namely the complex optical polarizability, along with all the optical cross sections.