Investigation On The Dispersion Compensation Of Femtosecond Optical Vortex Generated By Hologram Grating

The investigation of femtosecond optical vortex has very important significance and application value in many fields,such as quantum communication,the optical trapping(especially,trapping for Bose-Einstein condensates),microstructure rotation in laser tweezers and spanners,super-resolution microscopy.The femtosecond vortex beam can be generated by computer-generated hologram grating,but because of the wide bandwidth of the femtosecond pulse,the dispersion effection will cause the mode distortion.At present,the methods of dispersion compensation in the paper that has been published are 2f-2f setup and 4f setup.This paper proposes a new method based on the lens imaging system and combined with computer-generated hologram grating,this method applies the law of lens imaging,Fresnel diffraction theorem and Gaussian beam propagation formula.The rationality of the method we proposed is showed on the calculation results.In the experiment,we have produced a femtosecond vortex beam with no mode distortion according to the above mentioned model and verified the feasibility of this method.The diffraction efficiency of this method is improved by the proposed method.