Optical limiting for microsecond pulses.
Optical limiting for microsecond pulses.
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DOI：
10.1063/1.3072560
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发表时间：
2009-02
期刊：
影响因子：
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通讯作者：
S. Gavrilyuk;Ji-Cai Liu;K. Kamada;H. Ågren;F. Gel’mukhanov
中科院分区：
文献类型：
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作者：
S. Gavrilyuk;Ji-Cai Liu;K. Kamada;H. Ågren;F. Gel’mukhanov
本文提出了微秒时域内脉宽激光脉冲非线性吸收和传输的动力学理论。一般理论适用于富勒烯C（60），因为它具有良好的光限幅特性，即较低的基态吸收和较强的三重态-三重态吸收。结果表明，强三重态-三重态跃迁的连续吸收是非线性吸收的主要机制。时间尺度的内在层次使耦合速率方程的绝热解有效，因此可以减少到一个单一的动力学方程的基态人口。这个人口的缓慢演变是由人口转移到三重态的有效速率和脉冲持续时间定义的。传输效应对光功率限制性能起着重要的作用。光场强度和三重态的布居数在脉冲传输过程中逐渐减小，非线性双光子吸收减弱，线性单光子吸收逐渐成为主要过程。这些性质不同的过程之间的竞争取决于场强、吸收体的长度和浓度。通过数值求解二维傍轴场方程和基态布居的有效速率方程，研究了脉冲的传输。
We present a dynamical theory of nonlinear absorption and propagation of laser pulses with duration in the microsecond time domain. The general theory is applied to fullerene C(60) because of its good optical limiting properties, namely, a rather low ground state absorption and a strong triplet-triplet absorption. It is shown that sequential absorption involving strong triplet-triplet transitions is the major mechanism of nonlinear absorption. The intrinsic hierarchy of time scales makes an adiabatic solution of the coupled rate equations valid, which therefore can be reduced to a single dynamical equation for the ground state population. The slow evolution of this population is defined by an effective rate of population transfer to the triplet state and by the pulse duration. The propagation effect plays an important role in the optical power limiting performance. The intensity of the field as well as the population of the triplet state decreases during the pulse propagation, and a weakened nonlinear sequential two-photon absorption is followed by a linear one-photon absorption which gradually becomes the dominating process. The competition between these qualitatively different processes depends on the field intensity, the length of the absorber, and the concentration. The pulse propagation is studied by solving numerically the two-dimensional paraxial field equation together with the effective rate equation for the ground state population.