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Zhen Wu

Title: Professor and Department Chair Email: zwu@andromeda.rutgers.edu Phone: 973-353-1311/5250 Fax: 973-353-1434 Office: 211 Smith Hall Research:Atomic and molecular physics, Laser spectroscopy and surface science.

We are interested in the surface interactions of spin polarized alkali metal atoms and inert gas atoms in optical pumping cells. Due to the surface interactions, the polarization in the vicinity (~10^-5 cm) of cell surfaces can differ significantly from that in the bulk, creating a large normal gradient of spin polarization near the surfaces. This normal gradient of the spin polarization at the surface palys an important role in the study of surface interactions of spin polarized species. Specifically, it determines the boundary condition of the spin polarization. We have measured the hyperfine polarization of Rb atoms at micron and sub-micron distance from the surfaces in both coated and uncoated cells. We find that under our experimental conditions the hyperfine polarization decreases rapidly near uncoated surfaces over a distance of the 10^-3 cm. We have been able to deduce the hyperfine polarization, its normal gradient and normal gradient coefficient of the Rb atoms at the surface in uncoated cells.

The hyperfine polarization near the surfaces is very sensitive to surface interactions, and therefore can be used to characterize the property of surfaces (see the 2D image below). The images provide direct evidence for the existence of the so-called "hot spots", where the Rb spin relaxation rate is faster than that in the bulk. The ability to quantify and map the coating quality in optical pumping cells will be helpful in developing coatings of good and reproducible quality.

Some Recent Publications:

(1) K. Zhao and Z. Wu, “Regionally Specific Hyperfine Polarization of ⁸⁷Rb in the Vicinity (~ 10^-5 cm) of Surfaces”, Phys. Rev. A, 71 , 012902-1-14 (2005).

(2) K. Zhao and Z. Wu, “Mapping surfaces using regionally specific hyperfine polarization”, Phys. Rev. A, 70, 010901(R) (2004).

(3) K. Zhao and Z. Wu, “Hyperfine Polarization and its Normal Gradient Coefficient of ⁸⁷Rb Atoms in the Vicinity (~ 10^-5 cm) of Coated and Uncoated Pyrex Glass Surfaces”, Phys. Rev. Letters, 91, 113003 (2003).

(4) K. Zhao and Z. Wu, “Atomic resonance behavior in laser-induced Rb atom desorption --- the effect of ambient gas atoms and molecules”, Phys. Lett. A, 299, 73 (2002).

(5) K. Zhao, Z. Wu and H. M. Lai, “Optical determination of alkali metal vapor number density in the vicinity (100 nm) of cell surfaces, , J. Opt. Soc. Am. B 18, 1904 (2001).

Some Previous Publications Related to the Current Research:

(6) Z. Wu, W. Happer, J. Daniels, and M. Kitano, " Experimental study of the coherent surface interactions of spin polarized ¹³¹Xe nuclei", Phys. Rev. A 42, 2774 (1990).

(7) Z. Wu, W. Happer, and J. Daniels, " Coherent Nuclear-Spin Interactions of Adsorbed ¹³¹Xe Gas with Surfaces", Phys. Rev. Letters, 59, 1480 (1987).

(8) Z. Wu, S. Schaefer, G. Cates, and W. Happer, "Coherent interactions of the polarized nuclear spins of gaseous atoms with the container walls", Phys. Rev. A 37, 1161 (1988).

Figure 1. Mapping of a damaged silicone-coated surface using regionally specific ⁸⁵Rb hyperfine polarization.