求翻译：饱和吸收是因组成介质的粒子（原子、分子或离子）从基态能级跃迁至第一激发态能级时所发生的非线性光吸收现象。现在讨论如图5.2.2所示的二能级系统的介质的饱和吸收过程。在频率 、光强 的激光与介质间的共振作用下，光子能量等于两能级的能量差，即 ＝1－0，基态（ ）的粒子吸收光子，受激跃迁至激发态（ ），其吸收截面(跃迁几率)为 。因为激发态的能级寿命较短，大部分粒子通过自发辐射（或无辐射弛豫方式）回到基态，弛豫时间为 ，跃迁几率为 ；少部分粒子以受激辐射方式回到基态，跃迁几率也为 。是什么意思？

正在翻译，请等待...

Saturated absorption is formed by the media particles (atoms, molecules or ions) from ground level to jump to the first excited state energy level of the non-linear optical absorption. It is now discussing such as shown in Figure 5.2 , the 2 level system of media saturation of the absorption process

Saturable absorption is formed by particles of the medium (atoms, molecules or ions) from the first excited state of the ground state energy level transitions to nonlinear optical phenomena that occur when the energy level. Discussion now as shown in Figure 5.2.2 media saturation of absorption proce