http://digital.library.wisc.edu/1793/8333 Materials from the research group of Professor Thad G. Walker http://minds.wisconsin.edu:80/retrieve/8428 http://digital.library.wisc.edu/1793/8333 http://digital.library.wisc.edu/1793/38145 Anisotropic Spin-Exchange Walker, Thad G. Kadlecek, Stephen Nelson, Ian Using measured spin-transfer rates from alkali atoms to 3He, combined with spin-relaxation rates of the alkali atoms due to 3He and 4He, it should be possible to di?erentiate between isotropic and anisotropic spin-exchange. This would give a fundamental limit on the 3 He polarization attainable in spin-exchange optical pumping. For K-He, we ?nd the limit to be 0.90?0.11. Wed, 25 Nov 2009 21:25:13 GMT http://digital.library.wisc.edu/1793/36468 Ultrasensitive Atomic Magnetometers Wyllie, Robert Wakai, Ronald T. Walker, Thad G. We have developed a novel, small-volume portable single-channel atomic biomagnetometer and have used it to detect adult MCG signals. The cryogenic-free magnetometer has sufficiently high sensitivity (20 fT/rt(Hz)) that it is fetal MCG capable. It detects two magnetic field components simultaneously and has a bandwidth of typically 50-100 Hz. Extensions to multiple channels will be described. Thu, 10 Sep 2009 16:01:38 GMT http://digital.library.wisc.edu/1793/36466 A Portable SERF Magnetometer for Biomagnetic Measurements Wyllie, Robert Recent developments on the UW SERF magnetometer. Thu, 10 Sep 2009 15:00:42 GMT http://digital.library.wisc.edu/1793/36464 A Portable Ultrasensitive SERF Atomic Magnetometer for Biomagnetic Measurements Proite, Nicholas Cook, Peter Li, Zhimin Wakai, Ronald T. Walker, Thad G. Wyllie, Robert We present a portable Rb cell atomic magnetometer suited for biomagnetic measurements. Working in the spin-exchange relaxation free regime, we demonstrate an initial white noise floor of 60 fT$/\sqrt {Hz} $. We show an adult magnetic cardiogram and demonstrate the feasibility of extending our measurements to fetal MCG. Based on previous experiments the noise floor can be further reduced by parametrically modulating the z-magnetic field, which also allows for the simultaneous measurement of the x and y field components using a single probe beam [1]. We will present the simple conversion of the magnetometer to a gradiometer that still uses a single probe beam. Finally, we discuss related technical advances over previous designs, including the replacement of bulky air convection heating apparatus by simple rf heating and an effective insulation material that allows 1 cm working distance from the subject at 180C temperature differential. [1] Z Li, R T Wakai, and T G Walker, Appl. Phys. Lett. 89, 134105 (2006) Thu, 10 Sep 2009 14:55:54 GMT http://digital.library.wisc.edu/1793/35675 Codes to accompany "Optically Pumped Atoms" Walker, Thad G. Happer, William Jau, Yuan-Yu Wed, 29 Oct 2008 22:58:59 GMT http://digital.library.wisc.edu/1793/34818 Physics Challenges for Spin-Exchange Optical Pumping of He-3 Walker, Thad G. Presentation given at the "Physics and Applications of Polarized Noble Gases" workshop at the University of Virginia, May 19, 2009. Thu, 28 May 2009 12:38:19 GMT http://digital.library.wisc.edu/1793/34816 DAMOP Student Symposium 2009 Walker, Thad G. Presentation given at the student symposium for DAMOP 2009, Charlottesville, VA, May 21 2009. Includes an introduction to Rydberg physics with a description of recent experiments done at the University of Wisconsin Wed, 27 May 2009 21:58:19 GMT http://digital.library.wisc.edu/1793/28232 Dynamics of Low Density Rydberg Gases Brekke, Erik Day, Jason O. Walker, Thad G. A state-dependent stimulated emission probe was used to investigate the coherent and dynamic properties of cold Rydberg atoms. 87Rb atoms were excited to various nl Rydberg states from a MOT via continuous two-photon excitation. A stimulated emission probe laser was then used to bring the Rydberg atoms down to the 6P3/2 state,allowing detection of decay photons as a Rydberg atom detection method. Phase-matched four-wave mixing was also achieved and the angular dependence investigated. This coherent process is optimized when detuned from the Rydberg state, giving as much as 40% phase-matched light. In addition, the stimulated emission probe technique shows that radiative processes dominate the Rydberg population dynamics on a time scale much faster than the natural radiative lifetime. Modeling suggests superradiant emission may be the dominant factor. Poster presented at DAMOP 2008. Mon, 09 Jun 2008 19:08:54 GMT http://digital.library.wisc.edu/1793/8345 RayTrace Walker, Thad G. This applet traces paraxial light rays through a user-specified system of up to 12 ideal thin lenses and apertures, allowing many simple optical instruments to be modelled. Three examples are given: coupling of light from one instrument to another, a Newtonian telescope, and a projector. Thu, 12 Mar 1998 22:58:59 GMT http://digital.library.wisc.edu/1793/8457 Non-Degenerate Four-Wave Mixing through Rydberg States in a MOT Day, Jason Brekke, Erik Walker, Thad G. In this work, we use a three-photon near-resonant process in a laser-cooled Rb vapor to achieve phase-matched four-wave mixing using an intermediate Rydberg state. Rydberg atoms in the 36D5/2 state are efficiently produced using a 780 nm/480 nm two-photon excitation detuned 500 MHz above the 5P3/2 intermediate state. When a 1019 nm laser stimulates emission down to the 6P3/2 state, the Rydberg atom populations are significantly depleted and 422 nm 6P3/2-5S photons are observed by photon-counting photomultiplier tubes. With the 780 nm, 480 nm, and 1019 nm lasers configured in a non-collinear phase-matched geometry, we observe a coherent 422 nm phase-matched signal that is up to 10 times larger than the non-phase-matched radiation. Under these phase-matched conditions, the incoherent radiation is partially depleted. These experiments demonstrate the ability to coherently manipulate ultracold atoms at optical frequencies using Rydberg states. Presented at the 2007 DAMOP meeting. Mon, 02 Jul 2007 21:15:23 GMT http://digital.library.wisc.edu/1793/8455 A Portable Ultrasensitive SERF Atomic Magnetometer for Biomagnetic Measurements Wyllie, Robert Li, Zhimin Cook, Peter Wakai, Ronald T. Walker, Thad G. We present a portable Rb cell atomic magnetometer suited for biomagnetic measurements. Working in the spin-exchange relaxation free regime, we demonstrate an initial white noise floor of 60 fT/sqrt {Hz}. We show an adult magnetic cardiogram and demonstrate the feasibility of extending our measurements to fetal MCG. Based on previous experiments the noise floor can be further reduced by parametrically modulating the z-magnetic field, which also allows for the simultaneous measurement of the x and y field components using a single probe beam [1]. We will present the simple conversion of the magnetometer to a gradiometer that still uses a single probe beam. Finally, we discuss related technical advances over previous designs, including the replacement of bulky air convection heating apparatus by simple rf heating and an effective insulation material that allows 1 cm working distance from the subject at 180C temperature differential. [1] Z Li, R T Wakai, and T G Walker, Appl. Phys. Lett. 89, 134105 (2006) Presented at the 2007 DAMOP meeting. Mon, 02 Jul 2007 20:02:04 GMT