高能激光大气传输热晕效应分析

【作者】 蒲桃园；

【导师】 吴健；

【作者基本信息】 电子科技大学 ， 光学工程， 2010， 硕士

【摘要】 高能激光在大气中传输会产生一系列的线性和非线性效应,其中热晕是一种重要的非线性效应。热晕效应是指高能激光在大气传输时,大气中的分子和气溶胶粒子对激光能量的吸收,使大气受热膨胀,引起局部折射率减小,最终使高能激光光束能量降低,光斑变大,光束发生畸变。本文以高斯光束为例,数值模拟了高能激光在大气中传输的稳态和瞬态热晕效应,详细地分析了各种参数对热晕的影响,讨论了如何减小热晕效应对高能激光传输的影响。论文的主要工作:1.介绍了大气分子对不同波长激光束的吸收和散射特性,采用Modtran软件模拟了激光波长在1.1μm-11.0μm二氧化碳、水和臭氧中的透过率;并分析了采用波长为10. 6μm的高能激光比3.8μm传输效果要好的原因。2.从近轴波动传输方程,结合等压近似下空气密度扰动方程推导了二阶微分方程组,即热晕方程。计算了产生热晕效应的功率阈值。3.通过积分算法,差分算法和快速傅里叶变换等算法分析了近轴光束光传输方程和等压近似下流体力学方程的数值解法,并且分析了每种算法的优缺点。采用Sinpson积分算法对连续高能激光大气传输热晕效应进行了数值模拟,并将模拟的结果和国内外的参考文献相比,吻合程度较好。根据数值模拟的结果详细地讨论了激光功率、大气横向风速、激光发射口径、及激光传输距离对热晕效应的影响。4.以准直高斯光束为例,详细地分析了瞬态脉冲效应的扰动解。对单脉冲进行模拟计算得到的结果是: t 3脉冲由于仅受到线性吸收的作用,使得其在大气传输中受到的热晕效应影响要比t脉冲小;对于两个长脉冲激光大气传输,脉冲重复数在0.7-2.0,其脉冲在靶面上的相对强度最大。更多还原

【Abstract】 A series of linear and nonlinear effects can be produced when high-energy laser propagated in the atmosphere. Among them, the thermal blooming is one of the important nonlinear effects. Thermal blooming effect is a phenomenon that the atmospheric molecular and aerosol particles of atmosphere will absorb laser energy which accordingly cause heating expansion and the decrease of the local refractive index when high-energy laser propagates in atmosphere. Eventually, the energy of this high-energy laser beam will be reduced, the spot of this high-energy laser beam will be larger and the wave-front of this high-energy laser beam will be distorted.Take Gaussian beam as an example, the impact of various parameters on the thermal blooming by numerical simulation of the steady and transient state of the thermal blooming effect in detail was analyzed and how to reduce the impact of thermal blooming effect on high energy laser propagation was discussed in this dissertation. The main contents of the dissertation are as follows:1. The absorption and scattering properties of the different wavelengths of laser beam are absorbed by atmospheric molecules was introduced; and to simulate the transmission of carbon dioxide, water and ozone in the 1.1μm -11.0μm wavelength by using the software Modtran; and analyzed the reason why the transfer results by using a wavelength of 10. 6μm of better than by using 3.8μm .2. Thermal blooming equations, which is a second-order differential system, were derived from the scalar wave equation for paraxial beams and perturbation equation of the air density in the condition of approximation of constant pressure. And the power threshold of the thermal blooming effect was calculated.3. The numerical solution of the paraxial beam propagation equations was analyzed and the hydrodynamic equations under the condition of constant pressure approximation by the integration algorithm, differential algorithm and fast Fourier transform algorithm, and compared the advantages and disadvantages of each method. Simulated the thermal blooming effect of continuous high-energy laser beam transmitted in the atmosphere with Sinpson integration algorithm. And good agreement is obtained by comparing with the numerical simulation results and references results at home and abroad. According to the results of numerical simulation, the impacts of the power of laser, the wind speed of atmosphere horizontal, the diameter of laser and the distance of laser propagated on the thermal blooming were discussed.4. Take Gaussian beam as an example, the perturbation solutions of the transient state pulse effect was analyzed in this dissertation. The results of simulation for single pulse show that: The effect of thermal blooming is relatively larger when t pulse beam propagated in the atmosphere than t3 pulse which is only caused by linear absorption. For two long pulse laser beams with pulse repetition number in 0.7-2.0, which are propagated in atmosphere, its relative strength is largest on the pulse target surface.更多还原