Retroreflection, which is also known as the cat-eye effect, occurs in many imaging systems. The laser beam that irradiates on the focused photodetector would be reflected along its entranceway, by means of which the focused imaging system could be easily discovered and located. The paper analyzes the present research status of retroreflection reduction techniques. It shows that the related techniques mainly focus on four aspects: defocusing, masking, filtering, and one-way optical device. However, there are still some apparent disadvantages among the above technical schemes, which are generally manifested in the severe loss of imaging quality and the restricted application scope. Along with the rapid development of parallel computing platforms in recent years, computational imaging is widely applied in many fields. The paper proposes two novel configurations of anti-laser reconnaissance imaging systems based on the wavefront coding and the light-field rendering. Applying the computational imaging techniques will hopefully achieve a substantial retroreflection reduction without severely degrading the imaging quality, which shows us a broad prospect.
Based on previous anti-cat-eye effect imaging techniques sacrificing too much imaging quality to achieve substantial retroreflection reduction, an anti-cat-eye effect imaging technique based on light-field imaging is proposed. Relevant studies have been carried out regarding the mechanism and effectiveness of both antilaser reconnaissance and blinding for this technique. By applying the Fresnel–Kirchhoff diffraction theory and defining the microlens array as a superposition of a series of microlens units, the retroreflection formation of the light-field imaging system is theoretically modeled. Based on the physical model, the influences of defocusing on the intensity distributions of spots on both the light-field detector and observation planes are further studied. The results show that, compared with a conventional system with the defocus invariant and flexible reconstruction properties, the light-field imaging system not only increases the interference and blinding thresholds by nearly one order of magnitude but also reduces both the retroreflection maximum intensity and the echo-detector receiving power by more than one order of magnitude, which sufficiently manifests the superior antilaser reconnaissance and blinding performances of the light-field imaging system.
The 1064nm fundamental wave (FW) and the 532nm second harmonic wave (SHW) of Nd:YAG laser have been widely applied in many fields. In some military applications requiring interference in both visible and near-infrared spectrum range, the de-identification interference technology based on the dual wavelength composite output of FW and SHW offers an effective way of making the device or equipment miniaturized and low cost. In this paper, the application of 1064nm and 532nm dual-wavelength composite output technology in military electro-optical countermeasure is studied. A certain resonator configuration that can achieve composite laser output with high power, high beam quality and high repetition rate is proposed. Considering the thermal lens effect, the stability of this certain resonator is analyzed based on the theory of cavity transfer matrix. It shows that with the increase of thermal effect, the intracavity fundamental mode volume decreased, resulting the peak fluctuation of cavity stability parameter. To explore the impact the resonator parameters does to characteristics and output ratio of composite laser, the solid-state laser’s dual-wavelength composite output models in both continuous and pulsed condition are established by theory of steady state equation and rate equation. Throughout theoretical simulation and analysis, the optimal KTP length and best FW transmissivity are obtained. The experiment is then carried out to verify the correctness of theoretical calculation result.
The plasma channel evolution tendencies are studied numerically with the change of initial conditions based on the Nonlinear Schrödinger Equation. Then, the accuracy of an optical scheme to detect the plasma density inside the filaments is certified numerically. A Gaussian beam with pulse width 50fs, radius 2.5mm ranging energy from 10mJ to 50mJ at interval of 10mJ are simulated to yield plasma channel. With the augment of energy, firstly, the beginning position of plasma channel tend to be drew back gradually whereas the end position of the channel can be putted forward in a gradient form instead of continuously. Secondly, the number of peaks add one each time when the energy increase 10mJ. Lastly, the radius of plasma channel barely changes with initial energy up from 10mJ to 50mJ. On the other hand, plasma channel produced by a Gaussian beam with pulse width 50fs, energy 50mJ ranging the radius from 2.5mm to 10mm at interval of 2.5mm are simulated. With the increase of initial beam waist, the plasma channel length becomes shorter. The channel becomes broader and broader whereas the length of the channel becomes shorter. In order to verify the rationality of the approximation, Nornaraki detecting scheme through interference of the probe laser has been tested with the numerical simulation. As a consequence, the integral of refractive index along the radius direction can be replaced by the product of average refractive index and plasma channel diameter.
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