We demonstrate a new photo-induced oxidation technique for tuning GaAs photonic crystal cavities using a $390~mathrm{nm}$ pulsed laser with an average power of $10~mathrm{mu W}$. The laser oxidizes a small $left(sim 500~mathrm{nm}right)$ diameter spo
t, reducing the local index of refraction and blueshifting the cavity. The tuning progress can be actively monitored in real time. We also demonstrate tuning an individual cavity within a pair of proximity-coupled cavities, showing that this method can be used to correct undesired frequency shifts caused by fabrication imperfections in cavity arrays.
