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Aplikasi Laser-Induced Breakdown Spectroscopy (LIBS) untuk bidang keamanan [LIBS for security]

Tanggal 15-20 Desember 2010 telah berlangsung sebuah konferensi akbar bidang chemistry, physics, and biology di Hawaii, USA. Konferensi yang berlangsung setiap 5 tahun sekali ini dihadiri oleh sekitar 13 ribu peserta baik dari kalangan ilmuwan, praktisi, perusahaan, dan mahasiswa. Ada 13 bidang kategori yang dipresentasikan dan salah satunya adalah bidang keamanan. Alhamdulillah paper yang telah didaftarkan terpilih sebagai pemenang untuk bidang kategori keamanan. Beberapa surat kabar Indonesia telah mempublikasikan diantaranya adalah detiknews.com, vivanews.com, dan koran suroboyo.com. Abstraksi dari paper yang dipresentasikan adalah sebagai berikut,

Laser-induced breakdown spectroscopy (LIBS) has recently become an emerging analytical technique for rapid quantitative analysis. However, it is known that powder is difficult sample to be analyzed by using standard LIBS technique due to the serious blow-off of powder sample. In order to solve this problem, the powder is usually prepared in the form of pellet prior to the analysis. In such a case, a large amount of powder is necessary. The other solution is the use of double-pulse laser technique. Unfortunately, this technique requires expensive equipment. In an effort to facilitate the application of LIBS to a tiny amount of powder samples, we have developed a unique technique utilizing the special characteristics of a transversely excited atmospheric (TEA) CO₂ laser. In the case of a TEA CO₂ laser, a strong and high-temperature gas plasma was produced when the laser was focused on the metal surface, while the metal itself was never ablated and damaged. This phenomenon never occurs in case of standard LIBS technique, in which a Nd: YAG laser is employed as an energy source. When the strong gas plasma was induced in He surrounding gas by the TEA CO₂ laser, a lot of metastable He atoms were produced in the gas plasma region. Those metastable He atoms can effectively be used for atomic excitation source (1). In this present technique, a tiny amount of powder sample (2 mg) was homogeneously mixed with 2 mg of silicon grease to avoid the blow-off of the powder. The mixture powder sample was then homogeneously pasted with a very thin layer of approximately 0.10 mm and a dimension of approximately 1 x 1 cm² on a nickel metal plate. The TEA CO₂ laser (750 mJ, 10 Hz, 200 ns) was directly focused onto the mixture sample layer (spot size of laser irradiation of 1 x 1 mm²) in He surrounding gas as shown in Fig 1(a). After 3 shots of laser irradiation, a strong He gas plasma was induced because the laser beam directly impinged on the metal surface. Figure 1(b) displays a photograph of the mixture sample after being irradiated by several laser shots. It is hypothesized that once the strong gas plasma is induced, a lot of He atoms are highly ionized. The He ions then recombine with electrons, gaining a lot of metastable He atoms populated in the gas plasma region. During the time, the mixture sample is vaporized and enters into the gas plasma region to be dissociated and excited via metastable He atoms (excitation energy of 19.8 eV).

Figure 2 shows emission spectra taken from explosive powder material of fireworks. It can clearly be observed that high emission intensities of K I 746.9 nm and K I 749.9 nm appear together with O I 777.9 nm as presented in Fig. 2(a). The similar spectrum profile was also obtained when we used KNO₃ powder in place of the fireworks. Furthermore, this present technique can also be employed to identify poisonous or hazardous elements in a tiny amount of powder sample with a detection limit of several ppm. The detail experimental results will be presented in the session.

References

[1] A. Khumaeni, K. Kagawa et.al., J. Korean Physic. Society. 55, 2441 (2009)

Semoga memberikan manfaat, amin.

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