Towed linear array array based on fiber laser hydrophone which had much research potentiality owing to its higher acoustic pressure sensitivity, smaller size and lower difficulty of multiplexing. Flow noise is one of the main sources of noise in the towed linear array system. It will compress the dynamic range of fiber laser hydrophone and reduce the detection ability to small signal. In this paper, the structure of a 4 channel fiber laser hydrophone towed linear array was presented, and the data of sea trial of flow noise was analyzed. The results shows that the influence of flow noise mainly concentrate on the low frequency band which under 500Hz, and the background noise level has increased nearly 70-80dB when the array is towed at the speed of 3 kn.
The water has a strong absorption and scattering of light radiation, resulting in a certain depth of the underwater world in the dark. Therefore, underwater optical detection technology based on active lighting has become the main mode of deep-sea photo detection. Using a 532nm narrow-pulse laser and a self-built gain CCD system to form a underwater laser rang-gated imaging system, the forward and backward scattering are modeled and analyzed. Underwater laser rang-gated imaging system, was studied by laser pulse jitter, thus lead to the door of the control signal, the open time (earlier/later), the relationship between secondary scattering and image contrast curve, puts forward an optimal pulse with door control strategy. The correctness of the model is verified by the method of simulation and calculation of the relative ratio of the images acquired by the actual underwater laser distance gating imaging system. The results show that when the imaging system is not saturated, the image quality is best when the gate and the laser pulse are optimally matched. The effects of early opening and delayed opening on the image quality are different, and the duration of the gate opening is equal to the laser pulse width. At that time, the image quality is not optimal, and the effects of laser pulse jitter and secondary scattering are not all unfavorable. Based on the model, the opening time and the gate opening time are determined according to the contrast curve. It is generally advantageous to open the door lagging behind, and the duration of the gate opening should be 1- 3 times the laser pulse width.
We propose a sub-wavelength structure on vanadium oxide film as an extra
absorption layer (i.e. absorber) based on surface plasmon resonance effects, enhancing
dual-band absorption in both middle wavelength infrared (MWIR) and long wavelength
infrared (LWIR) region. Simulation results show that the absorber with disk structure has two
absorption peaks at wavelengths λ=4.8μm and λ=9μm with the absorption magnitudes more
than 0.98 and 0.94 in MWIR and LWIR region, respectively. Similarly, simulation results
show that the absorber with square structure has two absorption peaks at wavelengths
λ=4.8μm and λ=9.2μm with the absorption magnitudes more than 0.99 and 0.99 in MWIR
and LWIR region, respectively.
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