  In previous work we have shown that positive streamers in pure nitrogen can
be guided by a laser-induced trail of low electron density. Here we show more
detailed results from such measurements. We show the sensitivity of this
laser-guiding on pressure p and found that the maximum delay between the laser
pulse and voltage pulse for guiding scales with something between $1/p$ and
$1/p^{2}$. We also show that when we use a narrower laser beam the laser
guiding occurs less frequent and that when we move the laser beam away from the
symmetry axis, guiding hardly is observed. Finally we show that laser guiding
can also occur in pure argon.
