Self-focusing of ps laser pulses (&lgr;=790 nm) due to the nonlinear Kerr effect is shown to provide an easy and flexible method for producing bulk structures with dimensions on the order of 10 &mgr;m without damaging the entrance or exit surfaces of the material. The depth at which damage occurs can be controlled by adjusting either the pulse energy or pulse length. A study of the dependence of structure depth on the square root of the laser power for a given pulse length provides a straightforward method for determining the nonlinear index of refraction (Kerr coefficient),n2. ©1998 American Institute of Physics.