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Two ruby laser systems employing multiple Q-switching technology have been developed to provide ruby laser light for high-speed photography. Potential applications include ballistics and flow visualization as well as non-destructive 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 on 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 has been developed to provide higher pulse energies, on 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 has been investigated. The energy within the individual pulses formed in the oscillator cavity has been successfully increased by propagating through an amplification section, without degradation of the temporal or pulse-to-2 pulse amplitude stability. Etalons for longitudinal mode selection and an iris for spatial mode selection have been incorporated into the lower energy system and an image of a reconstructed hologram is presented. Camera capabilities and the implications of higher pulse energies have also been investigated.

The results of a combined experimental and numerical study on droplet behavior within an electrohydrodynamic fine spray are presented. The fine spray exists in the transition region between the multiple cone-jet and rim emission spray modes. Experiments were conducted specifically to characterize the motion of droplets within the spray. Light-sheet visualizations and measurements of droplet speed and velocity using laser-based, single-particle counters were obtained. Additionally, a numerical simulation of the droplet motion within the spray was made.and compared to the experimental results. The electrohydrodynamic fine spray of ethanol droplets ( ~ 1 to 40 pm diameter) was generated using a typical capillary-plate configuration, with a capillary tip electric field intensity of ~ 106 V/m and a spray charge density of ~ 70 C/m 3. Acquired images of the spray revealed a zone of rapid expansion near the capillary followed by a more gradual expansion farther from the capillary. In situ laser-diagnostic measurements confirmed these observations. Measured droplet speeds decreased rapidly with increasing axial distance from the capillary, but then increased beyond the spray's axial mid-plane as a result of a change in the sign of the axial internal electric field. Droplet axial velocity components behaved similarly. The radial velocity components exhibited a maximum value off of the spray's centerline in the nearcapillary region. Farther away from the capillary, they increased monotonically with increasing radial position. These trends identified the significant role that the radial internal electric field plays in spray expansion. The numerical simulation of the normal spray verified the inferred change in sign of the axial internal field and underscored the dominant contribution of the external electric field in the near-capillary region and of the internal electric field farther away.

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