To meet the ignition system needs of future lean- burn natural gas engines a diode side pumped, passively Q-switched, Nd: YAG laser was developed and tested. Laboratory experimentation used a wide range of input parameters that when combined produced brilliant sparks in air. The results show a strong dependence of the output on the output coupler reflectivity, Q-switch initial transmission, and gain media dopant concentration. The results show peak power levels of up to 3MW and peak focal intensities of up to 560 GW/cm2. Engine testing was performed on a Ricardo Proteus single cylinder...