  Measurement of local temperature using label-free optical methods has gained
importance as a pivotal tool in both fundamental and applied research. Yet,
most of these approaches are limited to steady-state measurements of planar
heat sources. However, the time taken to reach steady-state is a complex
function of the volume of the heated system, the size of the heat source, and
the thermal conductivity of the surroundings. As such, said time can be
significantly longer than expected and many relevant systems involve 3D heat
sources, thus compromising reliable temperature retrieval. Here, we
systematically study the thermal landscape in a model system consisting of
optically excited gold nanorods (AuNRs) in a microchamber using optical
diffraction tomography (ODT) thermometry. We experimentally unravel the effect
of thermal conductivity of the surroundings, microchamber height, and pump
pulse duration on the thermodynamics of the microchamber. We benchmark our
experimental observations against 2D numerical sumulations and quantitative
phase imaging (QPI) thermometry. We also demonstrate the advantage of ODT
thermometry by measuring thermal landscapes inaccessible by QPI thermometry in
the form of non-planar heat sources embedded in complex environments such as
biological cells. Finally, we apply ODT thermometry to a complex dynamic system
consisting of colloidal AuNRs in a microchamber.
