Using a novel technique , we achieve { \sim } 100 picoarcsecond resolution and set an upper bound of less than 4 km for the characteristic size of the Vela pulsar ’ s emission region .
Specifically , we analyze flux-density statistics of the Vela pulsar at 760 MHz .
Because the pulsar exhibits strong diffractive scintillation , these statistics convey information about the spatial extent of the radio emission region .
We measure both a characteristic size of the emission region and the emission sizes for individual pulses .
Our results imply that the radio emission altitude for the Vela pulsar at this frequency is less than 340 km .