Dirk Scheel

Fiber-optic laser sensor for mine detection and verification

What we believe to be a new optical approach for the identification of mines and explosives by analyzing the surface materials and not only bulk is developed. A conventional manually operated mine prodder is upgraded by laser-induced breakdown spectroscopy (LIBS). In situ and real-time information of materials that are in front of the prodder are obtained during the demining process in order to optimize the security aspects and the speed of demining. A Cr4+:Nd3+:YAG microchip laser is used as a seed laser for an ytterbium-fiber amplifier to generate high-power laser pulses at 1064 nm with pulse powers up to E(p) = 1 mJ, a repetition rate of f(rep.) = 2-20 kHz and a pulse duration of t(p) = 620 ps. The recorded LIBS signals are analyzed by applying neural networks for the data analysis.

Laser-induced plasma spectroscopy for mine detection and verification

Laser-induced breakdown spectroscopy (LIBS) in combination with a conventional mine prodder is applied for remote detection of explosives and mine housing materials. High power subnanosecond laser pulses (pulse power E p = 0.6 mJ and pulse duration Δ t = 650 ps) at 1064 nm with a typical repetition rate of 10 kHz are generated by using a passively Q-switched Cr 4+ :Nd 3+ :YAG microchip-laser as seed-laser for an Yb-fiber amplifier. In the present investigation, the ratios of “late” and “early” LIBS intensities for the cyanide (CN) plasma emission at 388 nm and for the C-emission at 248 nm are used for data analysis. This allows the classification of different explosives and mine casing materials under real time conditions and also similar applications to materials processing.

Real-time detection of mines and explosives by laser-induced breakdown spectroscopy

A fiber coupled LIBS system is used for detection of mines and explosives. Laser excitation at 1.5 mum is preferred to generate LIBS signals using an Er:glass microchip laser as seed laser for an Yb:Er fiber amplifier.

Evanescent-field laser sensor for in-situ monitoring of volcano gas emissions

A DFB laser diode (1.57 µm) is guided through a pure core fused silica fiber. Tuning the laser frequency across molecular resonances will change the frustrated (FTR) and the attenuated total reflection (ATR). Such an evanescent-field laser sensor is used for in-situ monitoring of H2S in volcano gases at the site “Solfatara”(Italy).