Nonlinear sharpening of holographically processed sub-microstructures
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- Hasegawa, S. & Hayasaki, Y. Appl. Phys. A (2013) 111: 929. doi:10.1007/s00339-012-7317-4
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Wavelength dispersion of a computer-generated hologram causes spatial broadening of the focal spot in holographic femtosecond laser processing. From the paraxial approximation, we theoretically derived that the spatial broadening is proportional to only the diffraction position, defined as the distance from the optical axis. We performed experiments under the large-dispersion condition to analyze the influence of the diffraction position on the processed structure. In the processing experiment, a high-numerical-aperture lens and a laser energy near the threshold energy were used to fabricate sub-microstructures. We found a nonlinear dependence of the broadening of the processed structures on the diffraction position, and the degree of broadening was much smaller than the predicted value because of the nonlinear properties of the laser processing.