The role of microwaves in the enhancement of laser-induced plasma emission

Abstract

We studied experimentally the effect of microwaves (MWs) on the enhancement of plasma emission achieved by laser-induced breakdown spectroscopy (LIBS). A laser plasma was generated on a calcium oxide pellet by a Nd:YAG laser (5 mJ, 532 nm, 8 ns) in reduced-pressure argon surrounding gas. A MW radiation (400 W) was injected into the laser plasma via a loop antenna placed immediately above the laser plasma to enhance the plasma emission. The results confirmed that when the electromagnetic field was introduced into the laser plasma region by the MWs, the lifetime of the plasma was extended from 50 to 500 µs, similar to the MW duration. Furthermore, the plasma temperature and electron density increased to approximately 10900 K and 1.5×10 18 cm −3 , respectively and the size of the plasma emission was extended to 15 mm in diameter. As a result, the emission intensity of Ca lines obtained using LIBS with MWs was enhanced by approximately 200 times compared to the case of LIBS without MWs.Keywords laser-induced breakdown spectroscopy, LIBS, microwave-assisted laser-induced breakdown spectroscopy, MA-LIBS, enhancement of laser plasma emission PACS numbers 42.62.Fi, 95.75.Fg,

Laser-Induced Breakdown Spectroscopy (LIBS): Fast, Effective, and Agile Leading Edge Analytical Technology

“…A second body of experimental approaches involves excitation of the vapor phase or of the particles induced by the ablation pulse with sources other than a laser. The most common approaches are based on excitation with high-voltage electrical pulses (Figure 8e), 47 microwave cavities (Figure 8f), 48 or glow-discharges (Figure 8g). 49 In the latter two situations, there is a need of a plasmogen gas (Ar or He) to support the secondary plasma.…”

Antenna Characteristics of Helical Coil with 2.45 GHz Semiconductor Microwave for Microwave-Enhanced Laser-Induced Breakdown Spectroscopy (MW-LIBS)

“…We previously reported on the application of pulsed microwave to laser-induced breakdown spectroscopy (LIBS), with breakthrough enhancements in plasma size and lifetime of air and gas mixtures [5][6][7][8], and a major increase in the emission signals of solid targets, such as Al 2 O 3 [9]. Applications of the MW-LIBS to Zr, Gd, wet Zr, and Mg were also presented [10][11][12][13][14][15]. The effect of multi-pulsed microwave in impeding the sputtering of the antenna, due to high temperatures at atmospheric pressure conditions, in contrast with a single continuous pulsed MW was also observed [9].…”

Aqueous ruthenium detection by microwave-assisted laser-induced breakdown spectroscopy

“…LIBS methods exploit the concept of atomic emission spectroscopy by using a laser pulsing in a range of nano-to femto-seconds as an ablation source. This approach allows analysis without the need for sample preparation as the laser energy is focused directly onto the sample allowing an ablation of the target regardless of its physical or chemical state [24,26]. However, LIBS suffers from the disadvantages of low sensitivity, and low reproducibility [27,28].…”