Plasma formation with nanosecond and picosecond Nd:YAG laser pulses was investigated as a function of laser pulse energy to find possibilities for a spatial reduction of the laser effects. The threshold for plasma formation (optical breakdown) in distilled water is 200 microJ for ns pulses and 15 microJ for ps pulses. At a pulse energy of 1 mJ, the plasma length is 80 microns for ns pulses and 250 microns for ps pulses. For the same pulse energy, ps plasmas are on average three times larger than ns plasmas. The plasma length is approximately proportional to the cube root of the laser pulse energy for both ns and ps laser pulses. The decrease in the breakdown threshold achieved by using ps pulses renders photodisruption with a smaller pulse energy (in the microJ range) possible, and therefore a reduction in the side effects. The results are compared with the "moving breakdown" model.