Reflective spiral phase plate for generating ultrashort optical vortices

Ultrashort pulses (picoseconds or less), are characterized by a high peak intensity that usually leads to nonlinear interactions. Recently ultrashort pulses with orbital angular momentum have attracted great attention due to their wide field of applications, from super-resolution microcopy, optical tweezers and ultra-fast optical communications to quantum computing and astrophysics. A principal challenge here is the development of robust and effective methods for OAM generation. At the moment few techniques are known to obtain OAM beams in the free space arrangement cylindrical lenses, spiral phase plates or computer-generated holograms have been used. All those techniques imply that pulse is passing through an optical component and thus obtain dispersive broadening. We propose here a method and a device allowing formation of ultrashort optical vortices from an incident ultrashort pulse without its broadening or compensating the pulse chirp acquired previously. Potentially method and device will allow obtain ultrashort vortices shorter than incident pulse. Case study is presented based on spatio-temporal numerical simulation and analytical modeling.