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Left: Correlation of LIBS molecular and atomic intensities with oxygen balance. Right: Variation in CN/C2 ratio versus oxygen balance for seven nitroimidazoles.

The technique of femtosecond laser-induced breakdown spectroscopy (FLIBS) was employed to investigate seven explosive molecules of nitropyrazole in three different atmospheres: ambient air, nitrogen, and argon. The FLIBS data illustrated the presence of molecular emissions of cyanide (CN) violet bands, diatomic carbon (C2) Swan bands, and atomic emission lines of C, H, O, and N. To understand the plasma dynamics, the decay times of molecular and atomic emissions were determined from time-resolved spectral data obtained in three atmospheres: air, argon, and nitrogen. The CN decay time was observed to be longest in air, compared to nitrogen and argon atmospheres, for the molecules pyrazole (PY) and 4-nitropyrazole (4-NPY). In the case of C2 emission, the decay time was observed to be the longest in argon, compared to the air and nitrogen environments, for the molecules PY, 4-NPY, and 1-methyl-3,4,5-trinitropyrazole. The intensities of the CN, C2, C, H, O, and N emission lines and various molecular/atomic intensity ratios such as CN/C2, CN(sum)/C2(sum), CN/C, CN(sum)/C, C2/C, C2(sum)/C, (C2 + C) / CN, (C2(sum) + C)/CN(sum), O/H, O/N, and N/H were also deduced from the LIBS spectra obtained in argon atmosphere. A correlation between the observed decay times and molecular emission intensities with respect to the number of nitro groups, the atmospheric nitrogen content, and the oxygen balance of the molecules was investigated. The relationship among the LIBS signal intensity, the molecular/atomic intensity ratios, and the oxygen balance of these organic explosives was also explored.

Good quality bulk size single crystals of inverse soluble lithium sulphate monohydrate (LSMH) have been grown by the modified Sankaranarayanan-Ramasamy (SR) method. A growth rate as high as 3 mm per day has been obtained for LSMH growth without substantially degrading the optical quality. The rocking curve recorded using the high resolution X-ray diffraction (HRXRD) technique reveals that the crystals grown by this method have a high degree of crystalline perfection. The optical quality of the crystals was studied using an UV-vis-NIR spectrum and the optical constants of the LSMH crystals were calculated. The laser damage threshold value of the grown crystals has been determined using a nanosecond Nd:YAG laser operating at 532 nm. Photoconductivity studies of the grown LSMH crystals reveal a positive photoconductivity behaviour of the grown crystals. The photoluminescence spectrum of the LSMH crystals shows a prominent emission peak at 373 nm. The third order non-linear optical properties of the LSMH crystals were investigated in detail by the Z-scan technique using a He-Ne laser operating at 632.8 nm. The non-linear refractive index (n 2 ), non-linear absorption coefficient (β) and third order non-linear susceptibility (χ (3) ) of the LSMH crystals were calculated.

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