Plasma induced by a pulsed CO2 laser from powder samples mixed with silicone on metal subtarget and its possibility for detecting difficult salts of Cl, B, and S

Abstract

Emission spectrum from plasma produced by a transversely excited atmosphere (TEA) carbon dioxide (CO2) laser from pure powder samples mixed with silicone grease attached to a nickel plate was studied. The pulsed CO2 laser operating at wavelength of 10.6 μm with energy and duration of the laser pulse is 2.5 J and 200 ns, respectively. The plasma was produced by focusing the laser beam onto the sample using a focusing lens (f = +200 mm) under air and helium surrounding gas at atmospheric pressure alternatively. The plasma emission spectrum was detected using an optical multichannel analyser (OMA) system equipped with a 0.32-m-focal length spectrograph. The spectrograph consists of a grating of 1200 graves/mm and a 1024-channel photodiode detector array with a micro-channel plate intensifier. The samples used this work are pure chemical powder samples. This technique was used to investigate emission spectral lines due to important salts but difficult to detect such as boron (B), chlorine (Cl) and sulphur (S) from powder samples. It was found that emission intensity detected from the produced plasma is remarkably higher in case using He as ambient gas compared with that using air. It was found that emission spectral lines due to B, Cl, and S can clearly be detected. Even though concentration of the salts (B, Cl, S) is very high since the samples used are pure chemical powder, however several emission spectral lines theoretically expected to appear with strong relative intensity displays relatively low intensity in the detected spectrum. This result confirms the difficulty for detecting the salts, especially chlorine (Cl) and sulphur (S). This technique basically promises a potential application for direct detection of B, Cl and S from powder samples, however new approaches must be developed to realise a high sensitive detection especially for Cl and S.