Laser/Lidar/Lips
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Laser / LIDAR / LIPS
Methods using lasers as a source provide the opportunity to investigate materials exciting them with high energy. These techniques are material specific and highly capable for explosives and landmine detection. The problems arise from the presumably high energy consumption of the laser and the possibvle ambiguity of the measurement results which requires a very sophisticated interpretation of the data.
LIDAR uses the angular distribution of the backscattered electromagnetic radiation to derive characteristics of the considered matter.
LIPS (Laser-induced plasma spectroscopy)is a type of atomic emission spectroscopy and can analyse any matter regardless of its physical state. A laser focused onto a small area at the surface of the specimen ablates a very small amount of material, which instantaneously generates a plasma plume with temperatures of about 10,000–20,000 K. At these temperatures, the ablated material dissociates (breaks down) into excited ionic and atomic species, called plasma. Within a very small timeframe the plasma expands at supersonic velocities and cools. At this point the characteristic atomic emission lines of the elements can be observed. Because all elements emit light when excited to sufficiently high temperatures, LIPS can detect all elements, limited only by the power of the laser as well as the sensitivity and wavelength range of the spectrograph & detector.
Raman spectroscopy is a powerful light scattering technique used to diagnose the internal structure of molecules and crystals. In a light scattering experiment, light of a known frequency and polarization (laser) is scattered from a sample. The scattered light is then analyzed for frequency and polarization. Raman scattered light is frequency-shifted with respect to the laser excitation frequency, but the magnitude of the shift is independent of the excitation frequency. This "Raman shift" is therefore an intrinsic property of the sample. Properties of the material can be determined by analysis of the spectrum, and/or it may be compared with a library of known spectra to identify a substance.
