AbstractPlasmonic nanolasers are a new class of laser devices which amplify surface plasmons instead of photons by stimulated emission. A plasmonic nanolaser cavity can lower the total cavity loss by suppressing radiation loss via the plasmonic field confinement effect. However, laser size miniaturization is inevitably accompanied with increasing total cavity loss. Here we reveal quantitatively the loss and gain in a plasmonic nanolaser. We first obtain gain coefficients at each pump power of a

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... plasmonic nanolaser via analyses of spontaneous emission spectra and lasing emission wavelength shift. We then determine the gain material loss, metallic loss and radiation loss of the plasmonic nanolaser. Last, we provide relationships between quality factor, loss, gain, carrier density and lasing emission wavelength. Our results provide guidance to the cavity and gain material optimization of a plasmonic nanolaser, which can lead to laser devices with ever smaller cavity size, lower power consumption and faster modulation speed.