High-frequency dielectric properties of A5B4O15 (A=Ba, Sr, Mg, Zn, Ca; B=Nb, Ta) dielectric ceramics are studied by means of the microwave cavity technique, a combination of far-infrared reflection and transmission spectroscopy and time-resolved terahertz transmission spectroscopy. Microwave permittivity ε′ and Q×f factor vary, depending on the chemical composition, between 11 and 51, and 2.4 and 88 THz, respectively. The temperature coefficient τf varies between −73 and 232 ppm/°C, and in two samples |τf| is less than 15 ppm/°C. It is shown that the microwave permittivity ε′ of the ceramics studied is determined by the polar phonon contributions and that linear extrapolation of the submillimeter dielectric loss ε″ down to the microwave region is in agreement with the microwave data of single phase samples. The relationship among phonon spectra, the crystal structure, and the unit cell volume is discussed.

We have identified and photographed individual cesium atoms in a magnetooptical trap with steep magnetic gradients. By switching off the trapping light fields, single atoms were released to a bound state of the magnetic potential. A storage time of 38 s was measured for purely magnetic trapping, whereas a storage time of 147 s was observed in the corresponding magneto-optical trap.

We have built a Zeeman-slower apparatus which produces a slow and cold cesium atomic beam. The atomic beam has a mean velocity in the range 35-120 m/s and a high atomic current of more than 2ϫ10 10 cold atoms/s. A small longitudinal velocity spread was achieved by optimizing the termination of the slowing process. The measured value of less than 1 m/s is consistent with a numerical simulation of the slowing process. With a magnetic lens and a tilted two-dimensional optical molasses stage, the slow atomic beam is transversely compressed, collimated, and deflected. We achieve a transverse temperature below the Doppler limit. The brilliance of this beam has been determined to be 7ϫ10 23 atoms s Ϫ1 m Ϫ2 sr Ϫ1. By optical pumping the slow atomic beam can be polarized in the outermost magnetic substates Fϭ4,m F ϭϮ4, of the cesium ground state. This brilliant beam is an ideal source for experiments in atom optics and atom lithography.

Using the stimulated force exerted by counterpropagating pulses from a mode-locked Ti:sapphire laser we have focused a beam of laser-cooled cesium atoms along one dimension to about 57% of its original width in the detection zone. We determined the force profile outside and inside the overlap region of the pulses and found agreement with an earlier theoretical prediction. The scheme does not require an effective two-level system and is therefore suitable for a large variety of elements. ͓S1050-2947͑97͒51011-0͔ PACS number͑s͒: 42.50.Vk, 03.75.Be, 32.80.Lg, 32.80.Pj RAPID COMMUNICATIONS R3356 56 A. GOEPFERT et al.