Biomedical subjects
Publications and source records attributed to Thad G Walker.
We describe a method to frequency narrow multielement high-power diode bars. Using a commercial 60-W, 49-element, 1-cm-long diode array bar at 795 nm running at 45 W, we narrow the linewidth from 1000 to 64 GHz with only a loss of 33% in output power. The resulting laser light is well suited for spin-exchange optical pumping of noble gas nuclei.
We apply light torques to single optically trapped glass nanorods suspended in water. The resulting motion is studied experimentally and consists of two distinct regimes: a linear regime where the rod angle increases linearly with time and a nonlinear regime where the rod angle changes nonlinearly, experiencing accelerations and rapid reversals. We present a detailed theoretical treatment for the motion of such nanorods, which agrees extremely well with the observed motion. The experiments are carried out so that the trapped and torqued nanorods move without influence from surfaces. Such a model system is critical to understanding the more complex motion that occurs near a surface. Studying such nonlinear motion both free of, and near, a surface is important for understanding nanofluidics and hydrodynamic motion at the nanoscale.
We demonstrate spin-exchange optical pumping of 3He using a "hybrid" K-Rb vapor mixture. The Rb atoms absorb light from a standard laser at 795 nm, then collisionally polarize the potassium atoms. Spin-exchange collisions of K and 3He atoms then transfer the angular momentum to the 3He with much greater efficiency than Rb-3He. For a K-rich vapor, the efficiency of the hybrid spin-exchange collisions approaches 1/4, an order of magnitude greater than achieved by pure Rb pumping. We present the first measurements of actual photon efficiencies (polarized nuclei produced per absorbed photon), and show that a new parasitic absorption process limits the total efficiencies for both hybrid and pure Rb pumping.