Fabrication And Characterization Of Vortex Beam Plate Based On Direct Laser Writing

Vortex beams have spiral wavefront phase and can carry orbital angular momentum,especially perfect vortex beams which the bright ring radius does not change with the change of topological charge.They are widely used in particle control,optical communication,quantum optics and laser manufacturing.At present,the generation of vortex beam is usually achieved by spiral phase plate,spatial light modulator or digital micro mirror device.Twophoton absorption direct laser writing technology has the processing accuracy that breaks through the limit of optical diffraction and the ability to process arbitrary three-dimensional structures,which has a wide range of applications in micro optical devices,micro fluid devices,life science and other fields.In this paper,two-photon absorption direct laser writing technology is used to fabricate a variety of spiral phase plates,and their optical characteristics are studied.The main research includes the following aspects:(1)The processing technology of femtosecond direct laser writing system was studied.Different three-dimensional structures were prepared by using SU-8 photoresist and IP-S photoresist respectively,and the effects of different processes on processing were studied.(2)The step spiral phase plate and continuous spiral phase plate which can generate vortex beam have been fabricated by using SU-8 photoresist,and their far-field intensity distribution and interference patterns are tested.The results show that the spiral phase plate prepared by direct laser writing has good optical characteristics.(3)Radial phase shifted spiral phase plates have been fabricated by using IP-S photoresist and demonstrated to generate perfect vortex beams.They not only have high relative focusing efficiency,but also can adjust the bright ring radius of the perfect vortex beam by changing the radial phase shift control parameters.The experimental results show that the radial phase shifted spiral phase plates prepared by direct laser writing also have good optical characteristics,and the theoretical design agrees well with the experiment.