15 March 1998 Near-field scanning optical microscopy: electromagnetic coupling between the aperture tip and the sample
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Abstract
The near-field scanning optical microscopy is widely applied in obtaining local optical information on the surface structures with subwavelength resolution. In the common illumination-transmission operation mode, the sample is illuminated by a near-field probe formed from an aluminum- coated, tapered optical fiber with subwavelength aperture and the transmitted light is collected by a conventional objective lens. Commonly the aperture tip is modeled according to Bethe's theory as the effective electric and magnetic dipoles whose magnitudes are only related to the incident electromagnetic fields. However, the coupling of the tip with the sample and the extended wafer can not be neglected as the tip is located in the proximity of the sample. In this work we treat the electromagnetic coupling of the tip with the sample and wafer in the real-space self- consistent approach and simplify the coupling of the wafer by the image method. The magnitudes of the effective dipoles are determined by the incident fields above the aperture as well as the perturbed fields reflected from below by the sample and wafer. When the coupling tip-sample-wafer system is solved in self-consistency, the transmitted optical signal collected by the lens can be derived straightforwardly, relating to the effective dipoles and the polarization of the sample. The simulation results show that the signal is sensitive to the polarization character of the incident fields.
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Ben-Yuan Gu, Zhi-Yuan Li, Guozhen Yang, "Near-field scanning optical microscopy: electromagnetic coupling between the aperture tip and the sample", Proc. SPIE 3276, Miniaturized Systems with Micro-Optics and Micromechanics III, (15 March 1998); doi: 10.1117/12.302392; https://doi.org/10.1117/12.302392
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