This work discusses time-resolved measurements of atomic and diatomic spectra following laser-induced optical breakdown. Spatially- and temporally- resolved spectroscopy is employed to characterize micro-plasma generated in laboratory air. Stark-broadened atomic emission profiles for hydrogen alpha and beta are utilized to determine plasma characteristics for specific time delays. The plasma dynamics include: variations in Stark-broadening emission of hydrogen alpha and beta lines, occurrence of molecular spectra due to recombination radiation, and change in line shape and appearance of atomic and molecular spectra due to collision and plasma oscillations. Comparisons of electron densities determined from hydrogen alpha and nitrogen II lines allow one to evaluate hydrogen self-absorption effects within the laser-induced plasma. Of interest are laser ablation measurements of atomic and diatomic emission spectra from aluminium (Al), aluminium monoxide (AlO), titanium (Ti), titanium monoxide (TiO), and carbon Swan systems that can be readily observed in laser-induced plasma. Diatomic molecules are frequently encountered in combustion processes. Optical breakdown emission spectroscopy data usually include signatures of species such as nitric oxide (NO), hydroxyl (OH), and cyanogen (CN) that allow one to characterize air plasma. The experimental work comprises measurement and data analyses of diatomic molecular spectra combined with computations of accurate line-strengths encompassing spectral superposition of both atomic and diatomic molecular species. Neodymium-doped yttrium (Nd:YAG) Q-switched, pulsed laser radiation is employed at the fundamental wavelength of 1064 nm to generate micro‑plasma in air. A standard Czerny-Turner type spectrometer is used together with an intensified diode array detector or an intensified charge-coupled device to record spectra.
View Full Article