Discuss Performance of Corner-Cube Prism for Modulating Retro-Reflector Terminal in Free-Space Laser Communication
Modulating Retro-reflector terminal does not need capture, tracking, targeting(ATP) sub-system .The key unit of this type structure is corner- cube prism,its performance will cause the light beam intensity distribution and light beam divergence angle .There are several factors ,such as effective area , right-angle accuracy, surface-type errors .Those errors caused loss of light power result in communication fail,so in this paper we made a precise analysis as a supplement.
Stability analysis and experimental measurements of the corner cube prism solid-state laser
Abstract In order to study the stability of corner cube prism solid-state laser under the effect of thermal lens, the resonant equivalence cavity, resonant G-parameter and auxiliary parameter theories were used to model the corner cube prism solid-state lasers containing a thermal lens. The laser stability with resonant cavity length was analyzed. In a stable condition, the beam radius was analyzed with regards to the distance from one of the corner cube prisms to gain medium by calculating the beam radius at each position under the resonator G-parameter theory. On this basis, a V-structured solid-state laser, pumped by a semiconductor laser and two corner cube prisms as a resonant, was built. In consideration of the effect of thermal lens produced by the pumped beam, the experimental measurements of the beam radius at two corner cube prisms and the gain medium were made for the resonant cavity length during stable condition of the laser. The experimental measurements agreed well with the simulation results, and showed that the maximum cavity length depended on thermal lens focal length of the gain medium, variation pattern in the beam radius at the corner cube prism, relationship between cavity length and the beam radius.
Analysis of the stress wave effect during coal breakage by a high-pressure abrasive air jet
In view of the defects of borehole collapse, inhibition of gas desorption and migration of gas existing in hydraulic fracturing and other hydraulic permeability–increasing measures for soft coal seams with low-permeability technology is proposed for coal breakage by a high-pressure abrasive gas jet for relieving pressure and increasing permeability. The comparative analysis of gas jet flow field structure between convergent nozzle and Laval nozzle has been given by numerical simulation. For Laval nozzle, the expansion wave and compression wave alternate and move forward steadily in gas jet and vanish when potential core length reaches maximum. So, the Laval nozzle can form more stable flow filed structure of gas jet and avoid shock wave in gas jet. Furthermore, a high-speed camera is adopted to analyze the jet structure and verify the conclusion of numerical simulation. Based on thermodynamic theory, this article calculates and analyzes the critical local sound velocity and pressure generated from the stress wave during the process of coal breakage by the gas jet. Furthermore, experimental coal breakage by a high-pressure abrasive gas jet is carried out. The high-pressure abrasive gas jet impacts the coal body as a quasi-static load and a dynamic load and forms corrosion pits on the surface of the coal body. Penetrating cracks are formed within the coal in the pattern of the loaded stress wave which leads to coal breakage. The effects of porosity and permeability on the propagation of the stress wave in coal are analyzed by establishing the dispersion equation for the spread of the stress wave in coal. The results show that porosity has a significant effect on wave velocity and that the attenuation of the stress wave is intensified with an increase in porosity. Moreover, the stress wave attenuation is more obvious at high frequency. The effect of permeability on the wave velocity is not significant at low frequencies. In contrast, at high frequency and relatively low permeability, the wave velocity increases with the permeability, and the attenuation of the wave velocity initially increases and then decreases. When the permeability is greater than 10−11 m2, the wave velocity is not affected by the permeability. However, the stress wave is not attenuated.