In this paper we report the first observations of dual-pulse laser-induced breakdown spectroscopy (LIBS) signal enhancements by using a pre-ablation spark. In this technique a laser pulse is brought in parallel to the sample surface and focused a few millimeters above it to form an air plasma or air spark. A few microseconds later a second laser pulse, which is focused on the sample, ablates sample material and forms the LIBS plasma from which analyte emission occurs. In this way, large LIBS signal enhancements, 11-to 33-fold, are observed for copper and lead, respectively, relative to the signal in the absence of the air spark. In all cases where enhanced LIBS signals are seen, greatly enhanced sample ablation also occurs.

In this paper, we investigate the effect of dual-pulse timing on material ablation, plasma temperature, and plasma size for pre-ablation spark dual-pulse laser-induced breakdown spectroscopy (LIBS). Although the plasma temperature increases for dual-pulse excitation, the signal enhancement is most easily attributed to increased sample ablation. Plasma images show that the magnitude of the enhancement can be affected by the collection optic and by the collection geometry. Enhancements calculated using the total integrated intensity of the plasma are comparable to those measured using fiber-optic collection.

No abstract

In this paper, we report the rst enhanced emission for elements in a nonmetal or nonconducting matrix, glass, with the use of a preablation spark. The glass samples used in this work are prototypes of samples used to immobilize inorganic waste at the Savannah River Site Vitri cation Facility. We have found that using a pre-ablation spark results in larger signal enhancements, 11-to 20-fold for titanium, aluminum, and iron in glass compared to the m etal under the same experim ental conditions. W e also demonstrate that this method is more sensitive than single-pulse LIBS experiments for the direct solid sampling of vitri ed waste glass.

In this paper, we investigate the effect of laser energy on laser-induced breakdown emission intensity and average temperature in a short-pulse plasma generated by using 140 fs laser excitation. Both line emission and continuum background intensity and plasma temperature decrease very rapidly after excitation compared to the more conventional nanosecond pulse excitation. Both emission intensity and plasma temperature increase with increasing laser energy. However, the intensity increase appears to be mostly related to the amount of material ablated. Also, nongated laser-induced breakdown spectroscopy (LIBS) is demonstrated using a high-pulse (1 kHz) pulse repetition rate.

Laser-induced breakdown spectra were measured by using a 1.3 ps laser pulse on glass, steel, and copper. Material ablation with the use of picosecond excitation is very precise with well-formed sharp-edged craters. The spectra obtained with 570 nm, 1.3 ps excitation decay more quickly and show significantly lower background emission than those that use 1064 nm, ∼ 7 ns excitation. The background was low enough that excellent laser-induced spectroscopy (LIBS) spectra were obtained on the three samples by using a single 1.3 ps laser pulse and a nongated detector. Similar results were obtained by using nanosecond excitation but with higher relative background signals. The radiance was similar with the use of pico- or nanosecond excitation; however, the radiant intensity was larger with nanosecond excitation because of the larger plasma.

In this paper, we report the first time-resolved laser-induced plasma images acquired using a liquid crystal tunable filter (LCTF). We also compare the use of LCTFs and acousto-optic tunable filters (AOTFs) for time-resolved plasma imaging applications in terms of resolution, out-of-band rejection, and image quality. Application of tunable filter technologies to plasma imaging is unlike other spectroscopic imaging methods because of the intense and spectrally broad background generated by a laser-induced plasma. High quality images of the distribution of atomic emission within a laser-induced plasma can be achieved using both AOTFs and LCTFs. However, additional filters are needed for rejection of wavelengths outside the tuning ranges of the devices. Both devices exhibited superior resolution in the lower working range of the filters (∼500 nm) with the LCTF exhibiting superior spectral resolution to the AOTF.

A fiber-optic probe designed for remote laser-induced breakdown spectroscopy (LIBS), Raman spectroscopy, and Raman imaging has been developed for the microanalysis of solid samples. The probe incorporates both single-strand optical fibers and an image guide and allows atomic emission and Raman analysis of any spot on a solid sample within a 5 mm diameter field of view. The real-time sample imaging aspects of the probe are demonstrated by measuring LIBS spectra from different regions of a granite sample and by measuring the Raman spectra of individual TiO2 and Sr(NO3)2 particles on a soil substrate. The ability to obtain remote Raman images of the TiO2 and Sr(NO3)2 particles on the soil substrate is also demonstrated. In this paper we discuss the design and implementation of the fiber-optic probe for obtaining LIBS spectra, Raman spectra, and Raman images.