Generation Of Scalar Hollow Laser Beam And Vectorial Hollow Laser Beam And Their Propagation Properties In Free Space

Dark hollow laser beams (DHBs) are the ring beams with zero center intensity in the propagation direction, which have spiral wave front, center phase singularity, and propagation invariance, and so on. So DHBs have many important and extensive applications in atom molecule optics, manipulation of the Micro-Nano particles, materials processing, quantum information, and so on.DHBs can be classified as scalar and vectorial hollow beam. During the past years, there have been a variety of technologies to generate scalar or vectorial hollow beams. In this paper, we propose two simple schemes to generate hollow beams:one method is to generate scalar beam by nonlinear crystal ZnSe. We study the generation principle of hollow beams based on nonlinear dielectric materials and optical system parameters on the effect of the hollow beam. Also, according to Huygens-Fresnel diffraction theory, we calculate the intensity distributions of the DHB and its propagating properties in free space, and study the dependences of the optimal propagation position and the dark-spot size (DSS) of the hollow beam on the waist radius of the incident Gaussian laser beam. Our study shows that the intensity distribution of the DHB presents symmetrical distribution with increasing the propagation distance, the optimal distance Zopt becomes farther and the DSS becomes larger with the increase of the waist radius w of the incident Gaussian laser beam. This generated DHB will have applications in the atoms or molecules trap.In addition, if the incident Gaussian laser beam is replaced by elliptical Gaussian beam or flattened Gaussian beam, we can obtain elliptical hollow beam or flattened hollow beam finally. What’s more, our study shows that the elliptical hollows maintain well for a long distance in free space.Another scheme is to generate a vectorial hollow beam (VHB) using a hollow metallic waveguide (HMW). The scalar hollow beam that generated by a 2π phase plate and lens incident to the hollow area of HMW. And a TE01 mode beam propagating in the free space is excited. Based on the vectorial Rayleigh-Sommerfeld diffraction integrals, and the propagation propertied of the generated VHB in free space after HMW are also studied theoretically. Our study shows that the intensity distribution of the generated beam presents hollow ring distribution and always maintain hollow in free space, also, the VHB appears similar self-focusing in free space. Moreover, we also study the dependences of the similar self-focusing position and the divergence angle of the VHB on the radius of the HMW, our study shows that the similar self-focusing position becomes farther and the divergence angle becomes smaller with the increase of the radius of HMW. In addition, the polarization of TEoi mode VHB maintain azimuthal polarization in free space, the VHBs can be applied to form Atomic molecular lens.