Formation of the periodic ripples on metallic surfaces is investigated comprehensively using variable ellipticities of femtosecond lasers. Compared with the linearly polarized incidence, the well defined grating-like ripple structures rather than the uniform arrays of nanoparticle can always be obtained for the elliptical polarization lasers. The ripple orientation is slanted clockwise or anticlockwise depending on the laser helicity but always display a maximum angle of 45°. Theoretical analyses indicate that no circular polarization is achieved for femtosecond lasers passing through quarter waveplate, and the induced ripple orientation is determined by the major axis of the polarization ellipse. The simulation results agree well with the experimental observations.
By analyzing the process of time delay integration dynamic imaging, we establish a
model of velocity mismatch. Based on this model, we analyze the
influence of different factors on the dynamic imaging process, and a
modulation transfer function (MTF) is used to evaluate imaging
quality. According to the simulation, the velocity mismatch and scan
stage are the main factors for image quality. The MTF of the image
sensor decreases with the velocity mismatch, and the scan stage
increases. In addition, an image with higher contrast can be obtained
in a short integration time. However, a shorter integration time leads
to insufficient sampling. Furthermore, we establish a dynamic MTF
testing system, and evaluate the experiment at different imaging
modes. Through data comparison, the experimental data are consistent
with theoretical data.
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