Influence of spatiotemporal coherence of broadband laser on beam smoothing of ISI

Abstract

The influence of the spatiotemporal coherence of the broadband laser on beam smoothing of the induced spatial incoherence (ISI) was analyzed. In such a scheme of ISI combined with lens array (LA) and polarization control plate (PCP), the broadband laser with spatiotemporal decoherence is adopted as the laser source, while ISI and PCP are employed to introduce spatial incoherence to the beamlets. Simulation results indicate that, the temporal decoherence arising from the broadband spectrum combining with the spatial decoherence induced by ISI and PCP brings about the ultrafast intensity variation of the focused spot and the spatial decoherence due to the application of partial coherent beam (PCB) mitigates the hard-edged diffraction effect of sub-beams arising from LA. As a result, the irradiation uniformity of the integral focused spot is significantly improved with a reduced time delay introduced to the pulse shape compared with the conventional ISI scheme. Besides, the requirement of the spatiotemporal decoherence can be further relaxed by optimizing the distance between the focal plane and the target plane, as well as the number of element lenses in LA.