The jitter is entirely atmospheric, and arises because the laser beam propogates upward along a different path to the downward propogation of the light from sodium fluorescence. Thus the LGS is seen to have about twice as much jitter as a normal star. The pixel scale here is around 0.43'', so the image motion is on the order of 1-1.5arcsec.

A single spot is useful when carrying out experiments on the laser beam, such as measuring the effect of polarisation on the spot brightness.