See Fig. 4 (a) and (b) in

Sho Itoh, Hirofumi Hidai, Hitoshi Tokura,
Experimental and numerical study of mechanism of glass modification process by continuous-wave laser backside irradiation (CW-LBI),
Applied Physics A
September 2013, Volume 112, Issue 4, pp 1043-1049
http://dx.doi.org/10.1007/s00339-012-7477-2