Repetitively pulsed ruby lasers as light sources for high-speed photography

Two ruby laser systems employing multiple Q-switching technology are developed to provide ruby laser light for high-speed photography. Potential applications include ballistics and flow visualization as well as nondestructive test evaluation using laser imaging diagnostics such as photography, holography, and various interferometric techniques. The laser systems produce more than 50 pulses at repetition rates up to 500 kHz with nearly constant pulse-to-pulse energies. One system, based on a commercial laser, provides multiple pulses of holographic quality light with individual pulse energies of the order of 10 mJ, pulse widths of 50 ns, and a pulse train length of more than 300 μs. A new ruby laser system is developed to provide higher pulse energies, of the order of 350 mJ per pulse, with 10 ns pulse widths and 140 μs pulse train length. The method for multiple Q-switching by modulating the Pockels cell’s quarter-wave voltage and the formation of an individual Q-switched pulse is investigated. The energy within the individual pulses formed in the oscillator cavity is successfully increased by propagating through an amplification section, without degradation of the temporal or pulse-to-pulse amplitude stability. E´talons for longitudinal mode selection and an iris for spatial mode selection are incorporated into the lower energy system and an image of a reconstructed hologram is presented. Camera capabilities and the implications of higher pulse energies are also investigated. © 1998 Society of Photo-Optical Instrumentation Engineers.