Optical dipole traps for cold atoms using diffracted laser light

We theoretically investigate the feasibility of using intensity distributions of light of a single laser beam diffracted by a circular aperture as optical dipole traps for cold neutral atoms. Localized and cylindrically symmetric traps on the central axis of the circular aperture exist for both blue- and red-detuned laser light. Experimental mapping of the spots of interest using ${\mathrm{CO}}_2$ laser light demonstrates the existence of these light distributions for laboratory conditions and their agreement with theoretical predictions.

Figure 1

(Color online) Calculated color image plot of the $z$ component of the Poynting vector versus $y$ and $z$ for plane-wave, $x$-polarized, 780-nm light incident upon a $25\text{−}\mathrm{\mu }\mathrm{m}$ aperture. The relative intensity is normalized to the intensity incident upon the aperture.

Figure 2

(Color online) Calculated on-axis intensity of the $z$ component of the Poynting vector versus the axial distance from the aperture plane for the same parameters as Fig. 1.

Figure 3

(Color online) (a) Illustration of the minimum escape path from the on-axis dipole trap for red- and blue-detuned laser light. (b) and (c) are the dipole trap depths (in $\mathrm{\mu }\mathrm{K}$ per $\mathrm{W}∕{\mathrm{cm}}^2$ of laser intensity incident upon the aperture) for ${}^{85}\mathrm{Rb}$ with $\Delta =-{10}^4\Gamma$ and $\Delta ={10}^3\Gamma$ versus position along the red- and blue-detuned minimum escape paths, respectively.

Figure 4

(Color online) Experimentally measured on-axis intensity distribution versus Hertz vector diffraction theory for $\lambda =10.61\mathrm{\mu }\mathrm{m}$ and an aperture radius of $205\mathrm{\mu }\mathrm{m}$.

Figure 5

(Color online) (a) Experimental scan of the beam profile for $\lambda =10.61\mathrm{\mu }\mathrm{m}$, $a=205\mathrm{\mu }\mathrm{m}$, $z=1.33\mathrm{mm}$, and (b) the radial beam profile versus Hertz vector diffraction theory.

Figure 6

(Color online) (a) Experimental scan of the beam profile for $\lambda =10.61\mathrm{\mu }\mathrm{m}$, $a=205\mathrm{\mu }\mathrm{m}$, $z=2\mathrm{mm}$, and (b) the radial beam profile versus Hertz vector diffraction theory.