基于光克尔效应的径向匀滑方案参数优化

Parameters Optimization for Radial Smoothing Based on Optical Kerr Effect

在基于光克尔效应的径向匀滑方案中,抽运光脉冲序列利用非线性介质的光克尔效应对激光束附加周期性的球面位相调制,从而使激光束远场焦斑内部散斑产生周期性的径向扫动,以改善远场焦斑均匀性。为了分析抽运光时间特性的改变对匀滑效果的影响,建立了径向匀滑方案的理论模型,并利用该模型对抽运光的时间特性参数进行了分析及优化。结果表明,在抽运光子脉冲之间的延迟时间一定时,子脉冲的脉宽过大或过小均会降低激光束远场的辐照均匀性,而随着子脉冲脉宽的增大,激光束远场的辐照均匀性随积分时间的波动相对趋于稳定,因而在避免产生明显"拍频"现象的前提下,选取较大的抽运光子脉冲脉宽更有利于实现稳定的匀滑效果。激光束与抽运光的时间同步精度对初期的匀滑效果有较大的影响,当抽运光提前1/5个周期左右时,可以在更短的积分时间内达到较好的径向匀滑效果。此外,不同的抽运光时间波形所获得的匀滑效果也有所不同,当抽运光的时间波形为三角波时,焦斑内部散斑的径向扫动速度较为稳定,可以使径向匀滑的整体效果及稳定性得到有效改善。

In the scheme of radial smoothing based on the optical Kerr effect,pump laser pulse train uses optical Kerr effect of nonlinearity medium to add periodical spherical phase modulation,which makes the speckle inside the focal spot of the laser beam in far field sweep periodically at radial direction,and the uniformity of the focal spot in far field is improved.To analyze the influence of temporal characteristics change of the pump laser on beam smoothing effect,a theoretical model of the radial smoothing scheme has been established,and the time characteristic parameters of the pump laser has been analyzed and optimized.The results indicate that,for the given delay time between pump photon pulses,the sub-pulse with either too large or too small pulse width will reduce the irradiation uniformity of laser beam in far field.Meanwhile,with the increase of the pulse width of sub-pulse,the volatility of irradiation uniformity of laser beam in far field with integral time is trending toward stability relatively.Thus,the relatively large pulse width of the pump laser would be beneficial to obtain a more stable smoothing effect under the condition that the obvious beat wave effect should be avoided as far as possible.The time synchronous precision between the laser beam and the pump laser has a significant influence on the initial beam smoothing effect.For the pump laser of about one fifth period of the pulse train in advance,a better smoothing effect can be obtained in a relatively shorter integral time.In addition,for different temporal shapes of the pump laser,different smoothing effects can be achieved.When the temporal shape of the pump laser is triangular,the radial direction sweeping speed of the speckle inside the focal spot is relatively stable,and the radial smoothing effect and its stability can be improved effectively.