In order to realize the laser and thermal infrared compatible stealth, a photonic crystal (PC) stealth film for 1064nm laser and mid-and-far infrared is designed by using the heterostructure method and characteristic matrix method. The results show that the reflectivity of this PC film at the wavelength of 1064nm is as low as 1%, meaning that it can reduce the reflectivity echo of 1064nm laser. In the meantime, the reflectivity of this PC film in 3-5μm and 8-14μm wavebands is 94.3% and 84.1% respectively, allowing the PC film to suppress the thermal radiation of the heat source. Furthermore, the impact of the incident angle on the reflectivity of the PC film is very small, whether in 1064nm wavelength or mid-and-far infrared wavebands. Therefore, this PC film can realize the compatible stealth of 1064nm laser and thermal infrared.
A compatible green stealth photonic thin films against near infrared and 1. 54μm laser, based on the structure of photonic thin films are designed to achieve compatible stealth of targets in background of green plants. Optical thin films have the advantage of regulating characteristics of the beam transmission. In this paper, the thin films are designed to simulate NIR Plateau of the spectral characteristics of green plants in the range of 0.78μm to 1.3μm and form a reflection Valley at 1.54μm. Based on the transfer matrix method (TMM) of thin-films optical theory , the Needle Algorithm and Tunneling Algorithm of thin-film automatic design methods are combined to optimize and design the green thin films. Finally, the near infrared green optical thin films with NIR spectral characteristics similar to the green plants are designed. And the spectral curve has a reflection valley near the center wavelength of 1.54μm ,and the reflectivity of the wavelength of 1.54μm is as low as 5%,achieving the stealth of the laser detector with the wavelength of 1.54 μm. On this basis, the influence of four incident angle of 0°,10°,20°and 30° on the spectral curve is analyzed. The results show that the spectral curves still meet the design requirements.
With the rapid development of optoelectronic technology, multi-band reconnaissance equipments have been widely used in the military field, which puts forward the requirement of multi-band compatible stealth for the targets. Actually, most of military targets, with strong heat sources, are hidden in the background of green plants. Therefore, to realize muiti-band compatible stealth means that the target surface should not only simulate the spectral characteristics of green vegetation in visible light and near infrared wavebands, but also have low emissivity in far infrared waveband to suppress the thermal radiation. However, it is difficult to obtain such special spectral characteristics for traditional coatings. A a new kind of man-made structure function material, photonic crystals (PC) could realize thermal infrared compatible because of its high-reflection photonic band gap. Firstly, taking ZnSe and Te as dielectric materials, a periodic PC film system is designed by using the characteristic matrix method. Then, using needle method, a method to design optical film system, ZnSe and the MgF2 films with different thicknesses are respectively inserted to the PC structure, and the ideal film structure is eventually obtained. This film material has a reflectance spectrum curve similar to that of green plants in 0.4-1.2 μm waveband. Simultaneously, the reflectivity in 8-12 μm band is 0.95, which can effectively reduce the thermal radiation intensity of the target surface. The above results show that this new type of film material can achieve multi-band compatible stealth for visible light, near infrared and far infrared bands under the greenwood background.
Terahertz (THz) radar system, with excellent potentials such as high-resolution and strong penetration capability, is promising in the field of anti-camouflage. Camouflage net is processed by cutting the camouflage net material, which is fabricated on pre-processing substrate by depositing coatings with camouflage abilities in different bands, such as visible, infrared and radar. In this paper, we concentrate on the propagation characteristic of THz wave in camouflage net material. Firstly, function and structure of camouflage net were analyzed. Then the advantage and appliance of terahertz time-domain spectroscopy (THz-TDS) was introduced. And the relevant experiments were conducted by utilizing THz-TDS. The results obtained indicate that THz wave has better penetration capacity in camouflage net material, which demonstrates the feasibility of using THz radar to detect those targets covered with camouflage net.
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