26-10-2017 дата публикации
Номер: US20170310071A1
Принадлежит:
A method for generating femtosecond vortex beams with high spatial intensity contrast, where a noncollinearly pumped HG beam femtosecond laser generates femtosecond HG beam and a cylindrical lens mode converter converts the femtosecond HG beam to femtosecond LG vortex beam. The HG beam femtosecond laser comprises a pump source, a gain medium, a saturable absorption mirror as mode-locker, and an output coupler with a noncollinear angle between the laser beam and the pump beam in the gain medium, which enables the laser to generate pure, order-tunable femtosecond HG beams. Femtosecond vortex beams obtained after the cylindrical lens converter have high-intensity-contrast, and are topological charge-tunable. 1. A method for generating femtosecond vortex beams with high spatial intensity contrast , comprising: a pump source for emitting a pump beam,', 'a gain medium,', 'three concave mirrors,', 'a saturable absorption mirror (SAM), and', 'an output coupler,, 'building a noncollinearly-pumped laser, said noncollinearly pumped laser comprising'}aligning the laser cavity to generate a laser beam from the output coupler,monitoring pattern of the output laser beam with a CCD camera,{'sub': '0n', 'rotating the output coupler to form a special angle θ between the laser beam and the pump beam in the gain medium so that the high-order Hermite-Gaussian beam is generated from the output coupler; the special angle θ determines an order of HGbeam having a lowest threshold pump power and being selected to oscillate, and n is 0 or an integer,'}optimizing position of the SAM to obtain stable mode-locking, and generating a high-order femtosecond Hermite-Gaussian beam from the output coupler,building a cylindrical lens mode converter to convert the high-order femtosecond Hermite-Gaussian beam into a femtosecond Laguerre-Gaussian vortex beam, and{'sub': '0n', 'aligning the cylindrical lens mode converter until a pattern of femtosecond LGbeam is obtained on the CCD screen.'}3. The method ...
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