In this paper, the spatial and temporal evolutions of the broadband chirped pulse with small-scale self-focusing (SSSF) in
nonlinear medium have been investigated by experiments and simulations. Firstly, we studied the spatial modulation
growth of broadband pulse by experiment in CS2 and the laser will produce many small peaks from perturbation
modulation. It is found that modulation growth of chirped optical pulses is delayed with the pulse chirp increasing. And
then we investigate the temporal evolution of the pulse at the modulation peak and bottom during the SSSF by numerical
simulation. The simulation results indicate that pulse width at modulation peak is decreasing with the increasing of
modulation peak intensity. But the pulse at modulation peak will broaden when the peak intensity reaches the maximum
and then the pulse began to splitting into two parts. However, the pulse width at modulation bottom always broadens and
finally reaches to a constant value. The simulation results are in agreement with the experimental results.
In this paper, we firstly preliminary analyzed how to control the collapse position of beam when intensity and beam
waist have been varied by the laser self-focusing in nonlinear media and lens-focusing. We obtain the relations of the
focusing position with input power and focal length of lens. The length of focusing is inversely proportional to the input
power and directly proportional to focal length of lens. Secondly, Based on the nonlinear propagation equation and
split-step Fourier method, we investigate how to control the focal distance and beam quality of high-power laser at
focusing spot in nonlinear media. We can control the focusing spot at any position by changed power and lens. The
numerical simulations is good consistent with theoretical analysis.
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