| dc.description.abstract | Laser-induced breakdown spectroscopy (LIBS) is a technique that utilizes intense laser pulses to generate a localized plasma that can be used for chemical analysis via quantifying the elemental composition of a sample. During the LIBS process, the emission generated from the plasma is collected, sent through a spectrometer and typically imaged using an intensified charged coupled devices (CCD) array. Unique spectral lines can then be detected, quantified, and assigned to specific elements that make up the sample. For the first time, to the best of our knowledge, a custom-designed pulse-burst laser operating at 100-kHz repetition rate was used for an ultra-high-speed LIBS application. While conventional LIBS methods utilize 10-Hz repetition-rate lasers, the higher repetition rate of 100-kHz allows for a faster sampling rate; specifically, during high-speed, short duration events such as explosions and shockwaves. Consequently, the potential benefits and applications of ultra-high-speed LIBS were explored using the pulse-burst laser system. In the preliminary studies, solid aluminum and copper targets were used for system characterization and calibration. Further studies were conducted to quantify the capabilities of high-speed LIBS for applications involving dynamic events lasting several milliseconds or less. Under the current experimental conditions, LIBS emissions from a high-exit-velocity air nozzle with additives of aerosol compounds were clearly recognized and detected at a high hit rate. Upon successful applications of the pulse-burst laser for preliminary testing, experiments were conducted during combustion of hydroxyl-terminated polybutadiene/ammonium perchlorate (HTPB/AP) propellants doped with varying concentrations of metals consisting of aluminum (Al), and lead (Pb). The pulse-burst laser LIBS system was successful in detecting the released metallic particles within the hot reaction zone of HTPB/AP propellants. A calibration study showed a relationship between the concentration of metals within the propellants and the hit rate at which the pulse-burst laser pulses interact with metallic particles. The limit of detection (LOD) of metal particles in the hot reaction zone was successfully calculated for subsequent applications of the pulse-burst-laser-based LIBS for predicting the metallic concentration with respect to the baseline case of 16% aluminum propellant samples. | en |
