A cost effective method for optical emission enhancement in laser-induced breakdown spectroscopy (LIBS) has been proposed in this research. The pulsed Nd:YAG laser with a wavelength of 532 nm was used for sample ablation and plasma generation. A cost effective commercial butane micro-torch was put parallel to the sample surface to generate a small flame above the surface. The laser-induced plasma expanded in the flame environment. The time-resolved optical emission intensity and signal-to-noise ratio (SNR) have been observed with and without micro torch. For laser with pulse energy of 20 mJ, the relationship between optical emission intensity and delay time indicates that signal intensities have been greatly enhanced in the initial several microseconds when using micro torch. The time-resolved study of signal-to-noise ratio shows that the maximum SNR occurs at the delay time of 2 μs. The laser energy effects on the enhancements of optical emission intensity and SNR have also been analyzed, which indicates that the enhancement factors are both delay time and laser energy dependent. The maximum enhancement factors for both optical emission intensity and SNR gradually decreases with the laser energy increase. The limits of detection (LODs) for aluminum (Al) and molybdenum (Mo) in steel have been estimated, which shows that the detection sensitivity has been improved by around 4 times. The LODs of Al and Mo have been reduced from 18 to 6 ppm and from 110 to 36 ppm in LIBS, respectively. The method of LIBS by a micro torch has been demonstrated to be a cost effective method for detection sensitivity improvement, especially in the situation of low laser pulse energy.
A technique was developed to achieve enhanced coherent anti-Stokes Raman scattering (CARS) imaging using selfassembled silica microspheres. In this study, a layer of optically transparent silica microspheres was self-assembled onto polymer grating samples to enhance the CARS signals. The highest enhancement of 12.5 was achieved using 6.1-μmdiameter microspheres for C-H molecule vibration. Finite-difference time-domain (FDTD) algorithm under the perfectly matched layer boundary condition was used to simulate the enhancement using silica microspheres of different diameters.
Improved spectral resolutions were achieved in laser-induced breakdown spectroscopy (LIBS) through generation of
high-temperature and low-density plasmas. A first pulse from a KrF excimer laser was used to produce particles by
perpendicularly irradiating targets in air. A second pulse from a 532 nm Nd:YAG laser was introduced parallel to the
sample surface to reablate the particles. Optical scattering from the first-pulse plasmas was imaged to elucidate particle
formation in the plasmas. Narrower line widths (full width at half maximums: FWHMs) and weaker self-absorption were
observed from time-integrated LIBS spectra. Estimation of plasma temperatures and densities indicates that high
temperature and low density can be achieved simultaneously in plasmas to improve LIBS resolutions.