Determination Of Orbital Angular Momentum States By Antiphased Semicircular Slit Pair

Determination of orbital angular momentum(OAM)states is a subject of crucial importance for their applications in areas ranging from classical physics to quantum information.Here,we propose the antiphase semicircular slit pair(ASSP)as a novel approach to determine the topological charge of OAM states.The ASSP contains two semicircular slits with a diameter increment and symmetrically arranged in upper and lower circle.It converts an incident OAM state into light field with two bright spots,of which the relative shift is twice as spot shift for a semicircular slit.Physically,we introduce the two models of equivalent spiral slit and the Young'slike interference,obtaining two approximate linear relations between the shift and the incident topological charge.Analytically,the antiphase of the diffracted fields for the two semicircular slits cancels a main Bessel vortex term,and doubles the complement fields contained in that for a single semicircular slit,realizing the field with two bright intensity spots with the relative shift doubled.The diffracted field is fundamentally approximated as the weighted superposition of finite Bessel vortex eigenstates.Using shift between the bright spots,the determination of topological charge of OAM states becomes a feasible and convenient,and the experimental measurement conforms to the theory with satisfying accuracy.In this thesis,the bright spots of the shift center of the optical field are obtained by the diffraction of a single semicircular slit under the illumination of the vortex beam.Two bright spots about the transverse symmetric shift of the center of the optical field are generated by using the antiphased semicircular slit pair(ASSP)formed by the additional phase shift ? to the lower semicircular slit with the decreased radius.The research contents of this thesis are as follows:1.We first introduce the development history of optical vortices and their applications in a wide range of classical and quantum sciences.Then,the optical vortices are analyzed mathematically in essence,and the spiral phase plate,computer-generated holograms,and multiple beam interference are classified and introduced,and the basic principles of each method are described emphatically.2.Through the basic introduction of optical vortices,we know that optical vortices have a very important research value in many fields.The determination of orbital angular momentum(OAM)states is a very important topic in the research fields from classical physics to quantum information.We also briefly introduce the background and status of optical eddy detection at the traditional and nanoscales.Several typical optical vortex detection methods are described and the basic principle of each method is analyzed,and the method of identifying optical vortices by nanoscale semicircle slit is analyzed.3.We verify for the first time that in the intensity distributions of the vortex beams diffracted by semicirular slit of traditional scale,a focused spot is formed though without the spin-orbit interaction,and the shift depends linearly on the topological charge m of the vortex beam.Based on the Huygens-Fresnel principle,we derive analytically the diffracted light field to be the superposition of the main Bessel vortex beam of topological charge m and a complement field.We introduce two models of the equivalent spiral slit and the equivalent Young's double slits of extended arc segments,to achieve the approximate linear relations of the spot shift with the topological charge.With the approximate linear relation,the robust map of shift between the two bright spots to input vortex beam provide a feasible means for determination of OAM states.The experimental measurement conforms well with the theoretical results.The work would be of significance to the areas related to the fundamentals and application of vortex beams?4.we propose the antiphase semicircular slit pair(ASSP)as a novel approach to determine the topological charge of OAM states.The ASSP contains an upper and a lower semicircular slits symmetrically arranged in a circle with a diameter increment to offer antiphase for the passing beam.The vortex beam is diffracted as two focused spots lying symmetrically aside the origin of the far-field observation plane,and the input OAM state is mapped to,and is discriminated with,the shift between the two spots,which is twice the spot shift for a semicircular slit.For the designed the ASSP,the half-wavelength optical path difference between two semicircular slits provides the inverse phase for its diffraction field.Therefore,in the output field,the antiphase of the fields diffracted by the two semicircular slits cancels the main Bessel vortex term,but doubles the complement fields,and thereby diffracted field includes two bright intensity spots with the relative doubled shift.More fundamentally,the output field are expanded as the weighted superposition of infinite eigen Bessel vortex states,and it is demonstrated that the field can be approximately substituted by the superposition of finite eigen states depending on the input topological charges.Using shift between the bright spots,the determination of topological charge of OAM states becomes a feasible and convenient,and the experimental measurement conforms to the theory with satisfying accuracy.