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Spaser Spectroscopy with Subwavelength Spatial Resolution

A new method for high-sensitivity subwavelength spectromicroscopy is proposed based on the usage of a spaser (near-field laser) in the form of a scanning probe microscope tip. The high spatial resolution is defined by the tip's curvature, as is the case for apertureless scanning near-field optical microscopy. In contrast to the latter method, we suggest using radiationless plasmon pumping by neighbouring quantum dots instead of irradiation of the tip by an external laser beam. The spaser generation spectrum is analyzed. The plasmon generation is suppressed due to absorption at the transition frequencies of the neighbouring nano-objects (molecules or clusters) under study. As a result, narrow dips appear in the wide plasmon generation spectrum. Further, the highest sensitivity is achieved near the spaser generation threshold. The sensitivity of the spaser spectromicroscope is estimated.