A brief survey is given of the progress made in the study and development of Q-switched lasers in recent years, and a review of the theory relevant to the work described, is outihed. A gain-switched giant pulse ruby laser system, employing two ruby rods of differing lengths in a single resonant cavity coupled with a rotating prism,has been developed. A systematic study of the output characteristics of this system under various conditions has been carried out. High resolution spectroscopy, including nanosecond time-resolution, of the emission of this laser, and also of a Pockels cell switched laser, has rendered possible the direct observation of the axial and off-axial mode structure, and has shown the existence of an intensity dependent frequency shift towards higher frequency in the giant pulses. When the two ruby rods in the gain-switched device are differentially cooled, simultaneous two frequency output pulses with powers in the tens of megawatt region are obtained, the wavelength separation of the two frequencies being tunable from 1 to 5.5Å. The suitability of this device for certain experiments in non-linear optics, such as the generation of the sum and difference frequencies in crystals, and nonlinear resonance mixing in plasmas, is considered. The two frequency output of the laser system has been mixed in ADP, to generate the sum frequency, and the conversion efficiency of the latter process compared with that of second harmonic generation.