This Letter presents a scheme to embed both angular/spectral surface plasmon resonance (SPR) in a unique far-field rainbow feature by tightly focusing (effective NA 1.45) a polychromatic radially polarized beam on an Au 20 nm∕SiO 2 500 nm∕Au 20 nm sandwich structure. Without the need for angular or spectral scanning, the virtual spectral probe snapshots a wide operation range (n 1-1.42; λ 400-700 nm) of SPR excitation in a locally nanosized region. Combined with the high-speed spectral

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... a proof-of-concept scenario was given by monitoring the NaCl liquid concentration change in real time. The proposed scheme will certainly has a promising impact on the development of objective-based SPR sensor and biometric studies due to its rapidity and versatility.