Joint Symposium on Nonlinear Optical Materials

QTuE5 Fig. 3 Map of a potential barrier for metastable argon atoms produced by a doughnut beam of 500 mW. The blue-detuning A is taken to be 15 times the natural linewidth r. The slope angle and exit hole of the he1 prism are assumed to be 60" and 0.2 mm, respectively. The Y axis shows the distance from the inner wall, while the Z axis indicates the distance along the fall line from the center of the exit hole. most 100% conversion rate. A Gaussian beam branches into two paths in the first refraction on the prism, and then a non- divergent doughnut beam appears after the second refraction. Figure 2b shows the intensity profile of the doughnut beam formed through the doublesone prism with a length of 4.25 mm and a diameter of 2.5 mm. The hollow diameter and ring thickness of the doughnut beams are determined by the prism length and the waist of the input Gauss- ian beam, respectively. The funnel can be available for reflec- tion of cold atoms fallen from a MOT. Figure 3 shows the potential barrier for metastable argon atoms expressed in terms of temperature, assuming the fun- nel prism with an exit hole of 0.2 mm and a slope of 60". The doughnut beam con- verted from the Gausian beam with a waist of 1.6 mm and a power of 500 mW produces the potential barrier of more than 1 mK through a distance of 3 mm along the fall line. Unless the funnel in- cludes some cooling mechanisms to com- pensate acceleration resulting from grav- itation, the atoms with the velocity of more than 10 cm/s cannot escape from the exit hole. Recently the addition of a weak pumping beam to cool atoms down to the recoil limit has been reported: The use of the additional beam propagating downward makes up for the lack of cool- ing mechanisms. Progress of the atom- guidance experiment will be also pre-