激光带宽抑制光束小尺度自聚焦效应的条件

激光带宽有利于抑制光束的小尺度自聚焦效应,从而突破非线性效应的限制提高高能固体激光器的输出功率。研究表明,带宽抑制小尺度自聚焦效应的程度与带宽和脉宽之比密切相关,相同脉宽条件下带宽越大对空间小尺度自聚焦的抑制作用越明显,而带宽一定时随着脉冲宽度的增大,带宽的抑制作用则逐渐变弱。在实际的钕玻璃激光放大系统中,由有限的增益带宽以及增益窄化等因素所限制的带宽量,决定了在这类固体激光系统中需要脉冲宽度短至皮秒量级才能有效利用激光带宽抑制小尺度自聚焦效应,而对于长至数十皮秒,甚至纳秒量级的长脉冲而言,如此有限的带宽量对小尺度自聚焦的抑制几乎不起作用。

Condition for Suppression of Small-Scale Self-Focusing of High-Power Laser Beams by Spectral Bandwidth

Broadband laser can be used to relax restriction of nonlinear effect and obviously improve output power of high-power solid laser systems, because of the spectral bandwidth of such kind of broadband laser can delay the onset of self-focusing. It is found that the degree of self-focusing suppression is closely related to the ratio of bandwidth and pulse duration, in the same pulse duration the bigger bandwidth is, the more obvious restraint effect is, and in the same bandwidth the restraint effect of bandwidth will become weaker with increasing the pulse duration. In actual neodymium-glass laser amplifying system, limited bandwidth can propagate through the amplification system due to the limited gain bandwidth and the gain narrow, which indicates clearly that the pulse duration as short as picoseconds is needed in this kind of solid laser system to achieve restrained small-scale self-focusing effect, while for longer pulse such as tens of picoseconds even nanoseconds, such limited bandwidth almost cannot influence the evolution of self-focusing.