High-power pulsed laser diodes are employed for determining atmospheric humidity and methane. The proposed DIAL method optimises the spectral properties of laser radiation within the molecular absorption bands of 0.86-O.9prn of these major greenhouse gases. The explicit absorption spectrum is explored by computational convolution method based on reference data on spectral linestrengths modulated by the characteristic broad laser line of the selected laser diodes. The lidar scheme is ultimately compact, of low-energy consumption and suggests a large potential for ecological monitoring.The distribution of atmospheric water vapour is very important for understanding the greenhouse effect and weather phenomena. Water cycle that maintains the process of atmospheric circulation is highly dynamic and is the main energy
Summary: Double‐heterodyne photodisplacement technique (PDT), based on the detection of the thermal expansion of a sample under irradiation by laser light has been employed to improve the resolution of photothermal displacement measurements up to orders of sub‐picometers. We have developed an ultra‐sensitive system to measure photothermal displacement of metallic and non‐metallic materials, such as silicon, due to the illumination by an ordinary laser diode. Non‐destructive characteristics of the scheme are well suited for conditions that restrict access to the sample to be measured. Careful consideration is given to eliminate the noise sources, so as to achieve the level of sensitivity that needed to detect the structural inhomogeneity of materials. Good agreement between experimental results and theoretical predictions is demonstrated.Laser double‐heterodyne detection of the photo‐thermal expansion of metallic and non‐metallic materials illuminated by a laser diode.imageLaser double‐heterodyne detection of the photo‐thermal expansion of metallic and non‐metallic materials illuminated by a laser diode.
A broadband differential absorption lidar (DIAL) is developed making us of the properties of high-power pulsed laser diodes for the purpose of monitoring methane, a major atmospheric greenhouse biogas. The detection range is optimized for the CH4 Q-branch 2v3 overtone spectrum centered at 1.667 μm and mixed with water-vapor absorption bands of. The resonance absorption evaluated of the DIAL signal is an integral sum of the multiple CH4 resonance absorption lines modulating the characteristic broad laser line and simultaneously compensating the interfering water-vapor absorption. A compact DIAL scheme is developed using an optimal configuration of high-power laser diodes matching the selected spectral parameters.
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