We introduce a new optical temperature measurement and thermal imaging technique combining near-field microscopy and Er3+ photoluminescence spectroscopy. We use the technique with two different approaches towards local temperature measurement and thermal imaging of optically excited gold nanostructures. In first approach, gold nanostructures on top of AlGaN:Er3+ thermal sensor film are optically excited under raster scanning with 532 nm CW laser through the Scanning Near-Field Optical Microscope (SNOM) cantilever tip to generate thermal images with the spatial resolution comparable to the true size of the nanostructures. In second approach, nanostructures on top of thermal sensor film on transparent sapphire substrate are excited with big spot size 532 nm CW laser (FWHM ~10 µm) from the bottom and the Er3+ emission from the film is collected in transmission mode through SNOM tip to experimentally map out the steady state temperature change under optical illumination. The steady state thermal images of the cluster of nanoparticles generated under near-field measurement reveal the thermal gradients within the hot spot which cannot be achieved by far-field measurement because of the insufficient spatial resolution. Steady state measurements under near-field also reveal the enhanced spatial resolution of the near-field yields the thermal profiles with good correlation to the theoretical steady state thermal profile.

Near field thermal imaging: Sub-diffraction and steady state thermal measurements on optically excited gold nanostructures

253rd National Meeting (2017)

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