Thermal Imaging of Nanostructures by Quantitative Optical Phase Analysis

Abstract

We introduce an optical microscopy technique aimed at characterizing the heat generation arising from nanostructures, in a comprehensive and quantitative manner. Namely, the technique permits (i) mapping the temperature distribution around the source of heat, (ii) mapping the heat power density delivered by the source, and (iii) retrieving the absolute absorption cross section of light-absorbing structures. The technique is based on the measure of the thermal-induced refractive index variation of the medium surrounding the source of heat. The measurement is achieved using an association of a regular CCD camera along with a modified Hartmann diffraction grating. Such a simple association makes this technique straightforward to implement on any conventional microscope with its native broadband illumination conditions. We illustrate this technique on gold nanoparticles illuminated at their plasmonic resonance. The spatial resolution of this technique is diffraction limited, and temperature variations weaker than 1 K can be detected.

Thermoplasmonics: Quantifying Plasmonic Heating in Single Nanowires

“…27 Thermal microscopy techniques have been demonstrated to probe temperature changes of small volumes including a thermographic phosphor technique, 28 scanning thermal microscopy, 29 and other methods. [30][31][32] This work combines electronic measurements with precise illumination to detect temperature changes isolated to the nanoscale volume of a single nanowire.…”

Quantitative absorption spectroscopy of nano-objects

“…The fundamental differences is that we do not modulate the heating and we do not perform the same kind of measurements: While the PTI techniques measure either a modulated scattered intensity, 5,13 or a combination of both the modulated intensity and phase gradient by DIC, 11 the QWLSI technique measures a quantitative 2D phase image. 6 Minding the phase and not the scattered inten-sity leads us to the possibility to quantitatively estimate the heat power delivered by the NP. Indeed, in the case of the PTI technique, a direct estimation of the ACS seems not possible as all the ACS measurements reported by the Berciaud, Lounis and coworkers were in arbitrary units.…”

“…6 This technique is based on quadriwave lateral shearing interferometry (QWLSI). Here, we follow this development and detail how to utilize a similar experimental procedure to achieve quantitative absorption spectroscopy on single absorbers.…”

“…6 This technique is based on quadriwave lateral shearing interferometry (QWLSI). Our present work follows this development and utilizes a similar experimental setup, which is presented in Fig.…”

“…More precisely, a modified Hartmann diffraction grating 7 produces an interferogram on a CCD camera that can be processed to quantitatively retrieve the optical wavefront profile of the probe beam. 6 In parallel, a CW Ti:Sapphire laser is used to heat the light absorbing metal structures. The wavelength of this infrared (IR) laser can be tuned from λ 0 =720 up to 950 nm.…”