| Femtosecond LASER is widely used in processing and imaging.Scanning is necessary in the application of femtosecond LASER.Acousto-optic scanning is a kind of high speed scanning technology.Acousto-optic deflector(AOD)is a kind of rapid and inertialess light beam scanner which is potential in the application of femtosecond laser scanning.But femtosecond laser has wide line width,and the AOD is a diffraction optical element which results in the dispersion.The conventional methods using gratings or prisms can not compensate the dispersion of AOD completely.Because the compensation supplied by gratings or prisms is constant,while the dispersion of AOD changes with the driving frequency.The conventional methods can only compensate the dispersion of AOD at a particular driving frequency.There is residual dispersion at other driving frequency.Here a novel method using a Keplerian telescope with high chromatic aberration to compensate the dispersion of AOD is proposed.The deflection angle of AOD is proportional to the light wavelength.The dispersion of AOD can be well compensated if the angular magnification of the Keplerian telescope is inversely proportional to the light wavelength.Furthermore,the Keplerian telescope can also elimate the spectra walk off effect which results in the temporal dispersion.I designed and developed the compensator based on Keplerian telescope.The simulation results show that this compensator has good imaging quality at 920 nm working wavelength within 0~3 degree field angle,and can compensate the dispersion within 20 nm light wavelength range.The experimental results show that the femtosecond laser beam reaches the diffraction limit within the working bandwidth of the AOD.Which indicates that the performance of the compensator achieves the expectation of the design.This dissertation solves compensation of the dispersion of femtosecond laser resulted by AOD.This work can expand the application of acousto-optic scanning of femtosecond laser. |
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