The spaser as a nanoscale quantum generator and ultrafast amplifier

Abstract

Nanoplasmonics has recently experienced explosive development with many novelideas and dramatic achievements in both fundamentals and applications. Thespaser has been predicted and observed experimentally as an active element—agenerator of coherent local fields. Even greater progress will be achieved if thespaser can function as an ultrafast nanoamplifier—an optical counterpart of theMOSFET (metal–oxide–semiconductor field effect transistor). A formidable problemwith this is that the spaser has inherent feedback, causing quantum generation ofnanolocalized surface plasmons and saturation and consequent elimination of the net gain,making it unsuitable for amplification. We have overcome this inherent problem andshown that the spaser can perform functions of an ultrafast nanoamplifier in twomodes: transient and bistable. On the basis of quantum density matrix (opticalBloch) equations we have shown that the spaser amplifies with gain with a switching time fs (potentially, ∼10 fs). This prospective spaser technology will further broaden both fundamental and appliedhorizons of nanoscience, in particular enabling ultrafast microprocessors working at10–100 THz clock speed. Other prospective applications are in ultrasensing, ultradense andultrafast information storage, and biomedicine. The spasers are based on metals and, incontrast to semiconductors, are highly resistive to ionizing radiation, high temperatures,microwave radiation, and other adverse environments.