The rapid development of artificial intelligence technology has brought new research concepts and methods to military application. Aiming to accelerate the research process of intelligent sensing technology and promote the landing application of human detection technology, this paper studies maritime military targets detection methods in infrared image sources and establishes a special detection model for this task, which utilizes sufficient visible samples to realize the hetero-source detection of infrared imaging targets. A detection model for cross-domain targets is trained through sufficient visible images, which realizes accurate target recognition in infrared images. Target information of different domain images is then fused and optimized, advantages of different-domain images are considered, and target detection features and results are combined to boost the performance of military target detection, thus laying the foundation for maritime real-time reconnaissance applications. A human detection method based on bounding boxes and a human detection method based on key points in visible images are proposed, which improves the detection accuracy of occluded and small targets in UAV aerial images. In order to bridge the gap between infrared images and visible images and improve detection accuracy in infrared images, hetero-source detection methods based on feature alignment and shared feature are put forward. Experiments are carried out on test set which is composed of randomly selected 487 images, and the proposed model achieves 84.8 AP, which is 4.8 higher than the famous Faster R-CNN, which proves the effectiveness of the proposed method.
We report a high-energy, high-average power burst-mode picosecond laser system, which is designed for space debris laser ranging. Pulses from a Nd : YVO4 mode-locked oscillator are first stretched by a piece of volume Bragg gratings (VBG) and then pass through an improved Michelson interferometer splitting system to obtain burst-mode pulses, which the relative amplitude and time-delay interval of each 4-pulse in bursts can be adjusted and controlled. A regenerative amplifier (RA), as a pre-amplifier, is adopted to decrease the repetition frequency of the seed beam from 80MHz to 1 KHz and raises the energy to millijoule-level. In order to reduce the performance requirement of the damage threshold of subsequent optical components and maximize the extraction of pulse energy, the Gaussian output beam of the RA is converted into a ring shaped pattern beam using an aspheric lenses reshaping system with the conversion efficiency of 93%. After a two-stage master oscillator power amplifier with 4f imaging systems, the pulse envelope energy is up to 100 mJ with the pulse duration of ~100 ps. To obtain high power green light, we compared the conversion efficiency of three crystals. When the fundamental frequency power is 80W, the second harmonic conversion efficiency of the first crystal (LBO, 6×6×10, Θ=90°, Φ=11.4°) is only about 50%, as well as the second (GTR-KTP, 7×7×7, θ=90°, Φ=23.5‡). But the conversion efficiency of the last crystal (LBO, 6×6×15, θ=90°, Φ=0°), reaches 68% and the output power of 532 nm as high as 50 W is obtained.
A single pulse energy 6.77mJ, repetition rate of 1kHz, pulse width of 11ps at 532nm wavelength with the near top-hat intensity profile in the near filed picosecond laser amplification system is realized using a semiconductor laser side pumped Nd:YAG crystal. The seed pulse is generated in a home-built Nd:YVO4 oscillator, pumped with a 808 nm CW diode laser. The oscillator provides 2.8nJ, 11ps pulse width, 86 MHz repetition rate at 1064 nm wavelength. Pulse from the Nd:YVO4 oscillator is first amplified to 1.5mJ by a diode side-pump Nd:YAG regenerative amplifier. Then the pulse, increased in size by a negative lens, sequentially passed through a circular aperture and a spatial filter-image relaying system to produce a top-hat intensity profile in the modules, and an 8th order super-Gaussian beam is obtained, and total transmission of beam shaping set-up is about 30%. The beam, passed through a double-pass preamplifier of single rod and a double-pass main amplifier of single rod, is amplified up to 17.3mJ, corresponding peak power is 1.57 GW. A 4F relay-imaging system is used in the amplification stages to preserve the top-hat intensity profile and compensate the thermally induced birefringence of Nd:YAG rod. The amplified output beam leaving the double-pass Nd:YAG module is decreased in size and imaged on a 5×5×13 m^3 second-harmonic generation (SHG) crystal-LBO by a 4F relay-imaging system, finally a 532nm approximate top-hat intensity profile in the near filed, which single pulse energy is 6.77mJ, is obtained after doublefrequency. The second-harmonic generation efficiency is over 51%.
Azimuthal polarization beam amplification up to an average power of 11.08 W using the Nd:YAG amplifier structure was obtained with the relative purity of 93% at 1 kHz.The beam quality factor M2 is 3.29 and the beam wavelength is 1064 nm. The amplification factor of the amplified picosecond azimuthally polarized beam is 207.9%.
A four-pulses sequence picosecond 1064nm regenerative amplifier system with repetition rate of 1 kHz are obtained, which with the average power of 9.2 W and beam quality M2 factor of 1.2. The Nd: YAG crystal with wedge angle of 2° and size of Φ 4×63 mm is adopted in the regenerative amplifier and around by three VCSEL pumping arrays with an angle of 120°. A laser diode (LD) pumped Nd: YVO4 crystal SESAM mode-locked seed laser is broadened from 20 to 260 ps by double-pass Volume Bragg Gratings and divided into equal amplitudes four-pulse sequence with the pulse spacing of 1ns by beam splitter mirrors. The four-pulse sequence enters the regenerative amplifier in order and the power is amplified from 0.68 to 9.5 W.
The effect of the gain medium planar shear stress, induced by non-radially symmetrical pumping during power amplification process, on the depolarization of radially polarized beam was analyzed in detail. For radially polarized beam, theoretical simulation had showed that the non-radial distribution of planar shear stress led to the different depolarization in different polarization directions, that the depolarization of the direction of 45° and 135° is five times more serious than that of 0° and 90°. In the following experiment, the radially polarized seed beam with a repetition rate of 1 kHz, an average power of 5 W and a pulse width of 100 ps was single-propagating double-rod Nd:YAG laser amplifier. Each rod was surrounded by three diode-pumped arrays with an angle of 120°. During the amplification process, the depolarization degree of radially polarized beam was 6.73%, which was obtained by measuring the difference between the power of the two beams transmitted and reflected by the analyzer TFP. The power of amplified radially polarized beam was 15.17 W with the purity of 89.3% and M2 of 3.95.
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