Laser technology and laser system has more and more important implication in spacecraft engineering. But different from ground environments, space laser system will encounter space environments include vacuum, extreme temperature and thermal cycling, vibration, space radiation environments such as electron, proton, heavy ions, ultraviolet, contamination, and so on. These space environments may have damage or threaten to the space laser system, especially to their optical devices. In this paper, space environments and effects are introduced firstly, and then the influence of space environments such as vacuum, temperature, energetic particles, contamination and vibration on space laser system are analyzed. At last, some advices are proposed to improve the reliability of space laser system are given.
Optical second surface reflector (OSR) is widely used as thermal control coating on the surface of spacecraft. Besides its thermal physics property such as solar absorption and thermal emissivity, its electrical property such as surface resistivity is used to prevent surface charging. Under the influence of space radiation environment, the surface electrical performance of OSR secondary surface mirror will be degraded, which will threaten the on-orbit safety and reliability of spacecraft. Based on the principle of dose depth distribution equivalence and total exposure equivalence, the influence of the space electron, proton and ultraviolet radiation environments on the surface electrical properties of OSR are experimentally studied, and its performance is in situ test. It was found that the resistivity of OSR secondary surface decreased exponentially with the increase of ultraviolet exposure and irradiation of electrons and protons. This shows that the surface conductivity of the OSR secondary surface mirror in space radiation environment increases and it has a better ability to resist surface charging and discharging effects.
Polyimide films are widely used in spacecraft, but their mechanical properties would degrade in space environments, such as electron, proton, near ultraviolet or far ultraviolet, etc. The mechanical property and mechanism of polyimide film in electron, proton, near ultraviolet and far ultraviolet was studied by Φ800 combined space radiation test facility of Beijing Institute of Space Environment Engineering (BISSE), and the degradation of mechanical property of polyimide film was tested by Electronic tensile testing machine. The tensile strength and the rupture elongation of PI film decrease with the increase of electron and proton radiation, while tensile strength and the rupture elongation of PI film decrease firstly and then increase with near ultraviolet and far ultraviolet.
Spacecraft will be damaged by space radiation environments such as electron, proton, X-ray, gamma ray, ultraviolet, and so on. For laser system used in spacecraft, its laser materials and laser devices will be damaged by laser beam. Besides, surface materials of spacecraft can be damaged by high energy laser too. So, spacecraft materials and devices may be damaged by synergistic effect of laser radiation and space natural radiation. In this paper, space radiation environments are introduced firstly, and then synergistic mechanism between laser and space radiation environments are discussed. Thirdly, test method for synergistic effect of laser radiation and space natural radiation on spacecraft is analyzed. At last, some directions are suggested to improve the space environment adaptability of spacecraft in space radiation environments and space laser radiation environment.
Laser technology and laser system has more and more important implication in spacecraft engineering. But different from ground environments, space environments include vacuum, extreme temperature and thermal cycling, space radiation environment such as electron, proton, heavy ions, ultraviolet, contamination, and so on. Space environments may have damage or threaten to the space laser system, especially to their optical devices. So the influence of space environments on the laser damage of space laser system should be studied. In this paper, space environments of space laser system encountered is introduced firstly, and then the influence of space environment on space laser system is discussed. Thirdly, the damage mechanism of space environment on laser damage is analyzed. At last, some works or countermeasures were proposed to improve the laser radiation damage threshold of laser system in space environments.
During its projected extended stay in LEO, spacecraft will encounter many environmental factors including energetic particles, ultraviolet radiation, atomic oxygen, and space debris and meteoroids, together with some induced environments such as contamination and discharging. These space environments and their effects have threat to the reliability and lifetime of spacecraft. So, it is important to give a combined design against the threat from space environments and their effects. The space environments and effects are reviewed in this paper firstly. Secondly, the design process and method against space environments are discussed. At last, some advices about protective structure and materials are proposed.
Polyimide films are widely used in spacecraft, but their mechanical properties would degrade in space environments, such as electron, proton, near ultraviolet or far ultraviolet, etc. The mechanical property and mechanism of polyimide film in electron, proton, near ultraviolet and far ultraviolet was studied by Φ800 combined space radiation test facility of Beijing Institute of Space Environment Engineering (BISSE. Rupture elongation of Kapton film decrease with the increase of the tensile deformation rate. The tensile strength and the rupture elongation of Kapton film decrease with the increase of electron and proton radiation, while tensile strength and the rupture elongation of Kapton film decrease firstly and then increase with near ultraviolet and far ultraviolet.
Glancing angle deposition (GLAD) is a novel way to produce nanostructural thin films with engineered porosity, and it is
possible to make new optical components in laser systems. In this paper, ZrO2, SiO2 and TiO2 thin films were grown by
electron beam evaporation with GLAD technique. Different microstructures were observed. The optical properties, such
as transmittance and refractive index were characterized. As application of the GLAD thin films, several optical
components were designed and fabricated, such as graded-index rugate filter, broadband antireflection coating and phase
retardater for visible and near infrared laser systems. Finally, laser-induced damage threshold were measured and
Reactive magnetron sputtering can be used to prepare graded index coatings. In this paper the relationship between the refractive index of the coatings and the partial pressure of reactive gas is discussed by experiment, in which A, O2 and Si are taken as sputtering gas, reactive gas and target material separately. And we have come to such conclusions that with the increase of partial pressure of reactive gas the color of the coatings turns shoal, the transmittance minimum of the coatings increases and the refractive index of coatings decreases according to the fitting rule of cubic polynomial. From XRD analysis, it can be seen that the coatings are identified to be amorphous.
Multi-layer dielectric grating is a key element used in chirped-pulse amplification technique. It includes high reflectivity film and periodic gratings on its top. Design of HR coating and top layer film (called multi-layer dielectric grating film) to produce gratings is important to fabricate such element with perfect optical properties and high laser induced damage threshold. In this paper, needle method is employed to synthesize the HR film with non-quarter wave coatings. The top layer is constructed by Fourier modal method, which is a rigorous method to analyze gratings. The synthesized multi-layer dielectric grating film shows good optical properties and electric intensity distribution.
By introducing scattering probability and statistical distribution functions of substrate subsurface defects' radius, refractive indices and positions, extended bidirectional reflectance distribution function (BRDF) was derived on the foundation of Jones scattering matrix. A numerical calculation of the extended BRDF for p-polarization incident light has been performed by employing Monte Carlo method. The calculating results indicate that the extended BRDF depends strongly on incident angle, scattering angle and azimuth angle, and presents a specific symmetry. For real refractive index, the extended BRDF is independent of subsurface defects' positions. And the extended BRDF will provide a more precise model for the calculation and measurement of polarized light scattering resulting from subsurface defects.
A model for refractive index of stratified dielectric substrate was put forward according to theories of inhomogeneous coatings. The substrate was divided into surface layer, subsurface layer and bulk layer along the normal direction of its surface. Both the surface layer (separated into N1 sublayers of uniform thickness) and subsurface layer (separated into N2 sublayers of uniform thickness), whose refractive indices have different statistical distributions, are equivalent to inhomogeneous coatings respectively. And theoretical deduction was carried out by employing characteristic matrix method of optical coatings. An example of mathematical calculation for optical properties of dielectric coatings had been presented. The computing results indicate that substrate subsurface defects bring about additional bulk scattering and change propagation characteristic in thin film and substrate. Therefore, reflectance, reflective phase shift and phase difference of an assembly of coatings and substrate deviate from ideal conditions. The model will provide some beneficial theory directions for improving optical properties of dielectric coatings via substrate surface modification.
The influence of inhomogeneous transitional layers on the spectral characteristics of AR coatings is discussed in this paper, and some results have been got: Inhomogeneous layers between substrate and coatings results in decreasing of the anti-reflection performance along with extremum shift to short wavelength; and among several kinds of inhomogeneous layers between two coatings, sine transition increases the anti-reflection performance, linearity, hyperbolae and exponent decrease the anti-reflection performance. Then a good fitting was given to the experiment of AR coatings and it was discovered that the sine transition between substrate and coatings is similar to experiment very well.