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Acta Physica Sinica

Theoretical and experimental study of a controllable double-dark-hollow beam

Qi Zhou, Lu Jun-Fa, Yin Jian-Ping

Published Jan 1, 2015• 2 citations

Abstract

A novel scheme is proposed for a double-dark-hollow beam (DDHB) based on non-full-range phase modulation with double-period. Upon illumination by a collimated He-Ni laser beam shaped by a round hole with a radius of 1.5 mm, the DDHB with an axial length of 30 mm, a width of 0.110.14 mm for each dark hollow beam and their separated distance being 57.6 m is generated in the image space of lens with a focal length of 200 mm. The proposed scheme has the advantages of simple construction and high controllability, and the separated distance between the two light pipes is only dependent on the factor of phase modulation of p. Under the given conditions, a reversible evolution process from a DDHB to a single dark hollow beam (SDHB) can be realized. Experiments for our scheme are performed, results of which are consistent with the theoretical ones. A valuable expansion of the application of DDHB in blue-detuned optical trapping is also discussed. Double and four well hollow optical traps, even the hollow optical lattices can be obtained by using various spatial combinations of our DDHB. The proposed DDHB is expected to play an important role in the study of trapping and manipulation of cold atoms or molecules.

DOI: 10.7498/aps.64.053701

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A novel scheme is proposed for a double-dark-hollow beam (DDHB) based on non-full-range phase modulation with double-period. Upon illumination by a collimated He-Ni laser beam shaped by a round hole with a radius of 1.5 mm, the DDHB with an axial length of 30 mm, a width of 0.110.14 mm for each dark hollow beam and their separated distance being 57.6 m is generated in the image space of lens with a focal length of 200 mm. The proposed scheme has the advantages of simple construction and high controllability, and the separated distance between the two light pipes is only dependent on the factor of phase modulation of p. Under the given conditions, a reversible evolution process from a DDHB to a single dark hollow beam (SDHB) can be realized. Experiments for our scheme are performed, results of which are consistent with the theoretical ones. A valuable expansion of the application of DDHB in blue-detuned optical trapping is also discussed. Double and four well hollow optical traps, even the hollow optical lattices can be obtained by using various spatial combinations of our DDHB. The proposed DDHB is expected to play an important role in the study of trapping and manipulation of cold atoms or molecules.

In this paper, we propose a new scheme to generate a dark hollow-beam, which includes dark hollow-beam optical pipe and hollow-beam optical dipole trap, through using a system composed of a four steps phase plate and a spherical lens. This kind of light beam can be used to focus, guide and trap the cold atom. We also calculate the intensity distributing and characteristic parameters of a dark hollow-beam and the optical dipole potential which manipulate the cold atoms of 85Rb. At last, we analyze and demonstrate the experimental feasibility of the scheme.

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We propose a new scheme to generate a focusing hollow beam (FHB) by use of an azimuthally distributed 2pi-phase plate and a convergent thin lens. From the Fresnel diffraction theory, we calculate the intensity distributions of the FHB in free propagation space and study the relationship between the waist w_0 of the incident Gaussian beam (or the focal length f of the lens) and the dark spot size (or the beam radius) at the focal point and the relationship between the maximum radial intensity of the FHB and the dark spot size (or the beam radius) at the focal point, respectively. Our study shows that the FHB can be used to cool and trap neutral atoms by intensity-gradient-induced Sisyphus cooling due to an extremely high intensity gradient of the FHB itself near the focal point, or to guide and focus a cold molecular beam. We also calculate the optical potential of the blue-detuned FHB for ^85Rb atoms and find that in the focal plane, the smaller the dark spot size of the FHB is, the higher the optical potential is, and the greater the corresponding optimal detuning delta is; these qualities are beneficial to an atomic lens not only because it is profitable to obtain an atomic lens with a higher resolution, but also because it is helpful to reduce the spontaneous photon-scattering effect of atoms in the FHB.

We propose a new method to generate a focused hollow laser beam by using an azimuthally distributed 2π-phase plate and a convergent thin lens, and calculate the intensity distribution of the focused hollow beam in free propagation space. The relationship between the waist w o of the incident collimated Gaussian beam and the dark spot size of the focused hollow beam at the focal point, and the relationship between the focal length f of the thin lens and the dark spot size are studied respectively. The optical potential of the blue-detuned focused hollow beam for 85 Rb atoms is calculated. Our study shows that when the larger waist w of the incident Gaussian beam and the shorter focal length f of the lens are chosen, we can obtain an extremely small dark spot size of the focused hollow beam, which can be used to form an atomic lens with a resolution of several angstroms.

A novel scheme based on light diffraction to generate a double-well optical trap for trapping and controlling two-species samples of cold atoms or molecules is proposed. Specialized phase modulation similar to the binary phase-grating is implemented in a diffraction device of liquid crystal spatial light modulator (LC-SLM). A continuous and reversible evolution between single-well trap and double-well trap is investigated. Corresponding experiments are performed and the results are in agreement with theories. Our results show that the proposed scheme has a controllability advantage, which is beneficial to the loading and controlling two-species samples in cold atoms or molecules experiments.

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