复杂激光系统中平板光学元件的调频-调幅效应的研究

Investigation on FM-to-AM conversation of the optical flat plates in complex laser systems

为了抑制大口径光学元件中的受激Brillouin散射效应,并满足打靶过程中束匀滑的要求,目前高能激光驱动器大都采用了正弦相位调制脉冲.然而,这类脉冲在复杂激光系统中传输时,会出现明显的调频-调幅(FM-to-AM)效应.研究这种效应的来源,对提升激光系统的整体输出性能至关重要.对复杂激光系统中一直被人们所忽视的平板光学元件带来的FM-to-AM效应进行了理论研究和数值模拟.数值模拟结果表明,通过平板光学元件的次数越多调制深度越大,呈线性递增趋势,当通过次数为10次时,调制深度高达22.2%;并且平板光学元件对各谱线的过滤也各不相同,当前端选用的中心波长为1054 nm时,平板光学对各谱线的过滤作用非常小.提出通过改变中心波长来减小FM-to-AM效应,这对于复杂激光系统的设计具有重要的指导意义.

At present, in most high-power laser drivers the phase modulation is used to suppress the effect of stimulated Brillouin scattering and meet the requirement for target surface light intensity uniformity. However, the modulated pulses show intense FM-to-AM effect after transmitted through a complex laser system. Analyzing the source of this effect is essential to the improvement of the output performance of whole laser system. In this paper, the theoretical analysis and the numerical simulation of the FM-to-AM conversion of the optical flat plates are investigated, which has been ignored by many researchers. The simulation results show that the more the laser passes through the optical flat plates, the deeper the modulation will be （for example, the modulation depth will be as high as 22.2% when transmitting ten times）, and it follows a linearly increasing trend. What＇s more, the different flat optical elements have different spectral filtering effects. When the central wavelength of the front-end is chosen to be 1054 nm, the spectral filtering effect is very weak. To our knowledge, the reduction of the FM-to-AM conversion by changing the central wavelength is presented for the first time.