In the military and civil fields, detecting small aircraft is of great significance. In recent years, the rapid development of LiDAR technology has made it possible to detect small aircraft at long distances. However, the scale change and attitude change make the detection difficult. Therefore, a detection network of multi-attitude small aircraft based on LiDAR anchorfree is proposed in this paper. The network structure is improved on the basis of the CenterNet network; using the encoder-decoder network structure, the extended convolutional module is designed to improve the receptive field and obtain the multi-scale information of the object. The IOU sensing branch is added to the detection header of the network to improve the localization accuracy of the object. The experimental results show that the detection accuracy of the improved network on the self-built simulation data set is 2.12% higher than that before the improvement and finally reaches 92.45%. Therefore, using this method can effectively improve the detection accuracy of the object.
Yb3 + : KY ( WO4)2 (Yb:KYW) possesses various excellent properties, such as its highly polarized emission cross section, that makes it an excellent option for developing highly efficient diode-pumped solid-state lasers. A high-energy, high-beam-quality passively Q-switched Yb:KYW laser was demonstrated. The small-signal gain characteristics of the Yb:KYW crystal under quasi-continuous-wave laser diode (LD) pumping were obtained by theoretical analysis. Under LD end-pumping at a repetition rate of 500 Hz and a pumping width of 200 μs, the Q-switched Yb : KYW / Cr4 + : YAG laser operated at a wavelength of 1025 nm, and a single-pulse energy of 0.5 mJ was obtained with a pulse width of 5.8 ns. Near-diffraction-limited beam quality with an M2 value of ∼1.02 was achieved. The compact setup provided efficient second-harmonic generation at 512.5 nm via type-I phase matching using a LiB3O5 (LBO) crystal, and the output single-pulse energy was 0.13 mJ. We believe that these results further demonstrate the utility of Yb:KYW as a passively Q-switched laser crystal for solid-state lasers, particularly for applications that require nonlinear frequency conversion.
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