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 research engine. The engine testing consisted of a comparison of the in-cylinder, and emissions behavior. All engine parameters were kept as constant and the equivalence ratio was varied between 0.8, 0.9, and 1.0. The test laser was constructed with a 30% output coupler, 32% Q-switch initial transmission, and a 0.5% Nd concentration rod all pumped by approximately 1000 Watts of optical power. The test laser single mode output pulse had an energy of 23 mJ, with a pulsewidth of 10 ns, and an M2 value of 6.55. This output produced focal intensity of 270 GW/cm2.