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Abstract
Here we investigate scanning photothermal microspectroscopic imaging of metal nanoparticles with reflective objectives. We show that correction-less collection of spectra from single spherical nanoparticles embedded in a polymer is possible over a wide spectral band, with large depth-of-focus, long working distance, and high lateral spatial resolution. We posit that these beneficial characteristics are inherent of the Bessel-Gauss character of the focused beam. When compared with other types of optical microscopy, the combination of these characteristics give photothermal imaging with reflective objectives an unique appeal for material characterization applications.