A sharply focused azimuthally polarized beam (APB) presents a strong longitudinal magnetic field with a vanishing electric field at its beam axis, forming an effective magnetic dominant region at the vicinity. This magnetic dominance is extremely desirable in the proposed high-speed ultra-compact optical magnetic force manipulation and microscopy, where the interaction between matter and the magnetic field of light can be exclusively exploited. However, direct characterization of such beam is challenging due to its subwavelength features. Here we show for the first time a direct characterization on a sharply focused APB in nanoscale using the novel Photoinduced Force Microscopy (PIFM) technique, which simultaneously excites and detects incident beam in near-field. Comparing to the Scanning Near-field Optical Microscopy (SNOM) which has near-field excitation and far-field detection, PIFM boasts a much smaller background noise and a more robust system. Based on the measured force-map, we develop a theoretical model to retrieve the corresponding electric and magnetic field distribution, and correct the distortion caused by the imperfect probe-tip of the PIFM. This research pioneers the exploration in the experimental investigation on the sharply focused structured light, unveiling its potentials in a plethora of optoelectronics, chemical, or biomedical applications.
Jinwei Zeng, Fei Huang, Caner Guclu, Mehdi Veysi, Hemantha K. Wickramasinghe, and Filippo Capolino, "Sharply focused azimuthally polarized beam characterized by photoinduced force microscopy (Conference Presentation)," Proc. SPIE 10350, Nanoimaging and Nanospectroscopy V, 103500T (Presented at SPIE Nanoscience + Engineering: August 08, 2017; Published: 21 September 2017); https://doi.org/10.1117/12.2273091.5583371263001.
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