A PMMA structure with different modified areas was tested in a configuration where a pulsed laser was injected from below (in a transversal way) and scattering near-field imaging (s-SNOM) was performed in a higher harmonic demodulation scheme.
The process of refractive index modification creates topographical changes as well, as it can be seen in the topography image below. When the structure was transversally illuminated, the laser injection can be inefficient (poor focalization) and s-SNOM detects mainly diffractive rings around each locally modified structure. However, when the focalization is done correctly, the s-SNOM image reveal Gaussian-shapes beams at the output of each modified area.
