[Portion of Introduction] In this chapter PL emission and THG by both CBD-grown and VPT-grown ZnO nanorod samples are reported. These studies clearly show that the low temperature PL emission from CBD-grown samples is both weaker in intensity and broader in terms of key feature linewidths than that from VPT-grown samples. By contrast the THG efficiency of samples grown by both the high temperature and low temperature methods are comparable to one another, and both are much larger than THG generated at a bare quartz surface. Intensity dependence measurement and interferometric frequency resolved optical gating (iFROG) measurements are used to study the THG from both sample types.[20,21] The laser pulse parameters are extracted when the pulses are subjected to both high and low chirp and our studies indicate that ZnO nanostructures grown by low temperature methods allow excellent characterization of ultrafast pulses (originally < 10 fs) and can efficiently generate THG. Consequently ZnO nanostructures grown by low temperature methods are excellent candidate materials for the technology applications discussed above.