Time-resolved shadowgraphic imaging of the response of dilute suspensions to laser pulses

Time-resolved imagery is presented showing the changes that occur in the focal volume of dilute liquid–particle suspensions following the arrival of single, $Q$-switched, frequency-doubled, Nd:YAG laser pulses. Data are presented for a carbon particle suspension consisting of used (carbonized) 10W-15 motor oil and for a suspension of the inorganic metallic cluster molecule ${\mathrm{Mo}}_2{\mathrm{Ag}}_4{\mathrm{S}}_8[{\mathrm{PPh}}_3{]}_4.$ The images in conjunction with the accompanying limiting data show that the reduction in transmission, observed as the input pulse energy is increased, results from scattering from bubbles augmented by plasma absorption. The imaging technique involves converting a portion of the laser pulse to probe pulses that are then delayed through varying lengths of optical fiber. The focal volume is probed perpendicular to the incident beam at various times from 12 ns to 2.9 μs after the arrival of the pulse in the test cell. Light emitted from the cell as a result of incandescence or a hot plasma is also imaged. Nonlinear loss, time-resolved pump–probe and picosecond limiting experiments, performed at the University of Central Florida’s Center for Research in Electro-Optics and Lasers (CREOL), are described in the companion paper in this issue entitled “Nonlinear optical properties of the inorganic metal cluster ${\mathrm{Mo}}_2{\mathrm{Ag}}_4{\mathrm{S}}_8[{\mathrm{PPh}}_3{]}_4.$”