High-Field Spin Exchange Optical Pumping of Cesium Salts An - - PowerPoint PPT Presentation

Spin Exchange Optical Pumping Experimental Setup Results

High-Field Spin Exchange Optical Pumping of Cesium Salts

An Experimental Project Ben Andrew Olsen

Princeton University Adviser: William Happer

November 12, 2007

Ben Andrew Olsen High-Field SEOP of Cesium Salts

Spin Exchange Optical Pumping Experimental Setup Results

1 Spin Exchange Optical Pumping

Basic Picture SEOP with Cesium Vapor CsH and CsF

2 Experimental Setup

Optical Pumping Setup High-Frequency NMR Probe

3 Results

Cesium Fluoride Cesium Hydride

Ben Andrew Olsen High-Field SEOP of Cesium Salts

Spin Exchange Optical Pumping Experimental Setup Results Basic Picture SEOP with Cesium Vapor CsH and CsF

Basics of SEOP

Optically pump alkali metal vapor Polarized alkali atoms in the vapor interact with atoms of another species Increase the net nuclear polarization of the other species (hyperpolarization)

Ben Andrew Olsen High-Field SEOP of Cesium Salts

Spin Exchange Optical Pumping Experimental Setup Results Basic Picture SEOP with Cesium Vapor CsH and CsF

Applications of Hyperpolarization

Fundamental Physics High energy physics: Spin polarized beams of particles Atomic physics: Spin-dependent interactions, gyroscopes In vivo Imaging Inhale hyperpolarized gas for lung imaging Inject or ingest hyperpolarized material to track intake into tissue

Ben Andrew Olsen High-Field SEOP of Cesium Salts

Spin Exchange Optical Pumping Experimental Setup Results Basic Picture SEOP with Cesium Vapor CsH and CsF

Basics of SEOP in Solids

Optically pump the alkali metal vapor Polarized alkali atoms diffuse toward cell walls Polarized alkali atoms in the vapor interact (and exchange) with alkali atoms in the solid Increase the net nuclear polarization of alkali atoms in the solid Detect net polarization using pulse NMR

Ben Andrew Olsen High-Field SEOP of Cesium Salts

Spin Exchange Optical Pumping Experimental Setup Results Basic Picture SEOP with Cesium Vapor CsH and CsF

A Cartoon of SEOP

Ben Andrew Olsen High-Field SEOP of Cesium Salts

Spin Exchange Optical Pumping Experimental Setup Results Basic Picture SEOP with Cesium Vapor CsH and CsF

A Cartoon of SEOP

Ben Andrew Olsen High-Field SEOP of Cesium Salts

Spin Exchange Optical Pumping Experimental Setup Results Basic Picture SEOP with Cesium Vapor CsH and CsF

A Cartoon of SEOP

Ben Andrew Olsen High-Field SEOP of Cesium Salts

Spin Exchange Optical Pumping Experimental Setup Results Basic Picture SEOP with Cesium Vapor CsH and CsF

SEOP with Cesium Vapor

Complications to our simple picture: I = 7/2: 8 levels with hyperfine structure Electron spin and orbital angular momenta are coupled Several transitions to pump Questions to answer: Do electron or nuclear polarization currents dominate SEOP? Can we polarize the other nuclei in the salt?

Ben Andrew Olsen High-Field SEOP of Cesium Salts

Spin Exchange Optical Pumping Experimental Setup Results Basic Picture SEOP with Cesium Vapor CsH and CsF

D2 Transitions in Cesium

Ben Andrew Olsen High-Field SEOP of Cesium Salts

Spin Exchange Optical Pumping Experimental Setup Results Basic Picture SEOP with Cesium Vapor CsH and CsF

Simulation of SEOP in Cesium

Electron spin current Js and nuclear spin current JI to the cell walls for some transitions: Transition Js JI (b+) − − (b−) + + (e+) + − Red indicates the larger magnitude current. At opposite polarization, the magnitudes of Js, JI decrease by a few orders of magnitude.

Ben Andrew Olsen High-Field SEOP of Cesium Salts

Spin Exchange Optical Pumping Experimental Setup Results Basic Picture SEOP with Cesium Vapor CsH and CsF

Cesium Hydride

Polarization enhancement by SEOP has been seen for Cs in CsH (K. Ishikawa et al., Phys. Rev. Lett. 98(18), 2007)

Enhancement by a factor of 4 for allowed transitions

We want to measure the dependence of enhancement on photon polarization Cells with such high Cs enhancement are good candidates for H enhancement For H in CsH, T1 ∼ 1000 s at room temperature For Cs in CsH, T1 ∼ 300 s at room temperature

Ben Andrew Olsen High-Field SEOP of Cesium Salts

Spin Exchange Optical Pumping Experimental Setup Results Basic Picture SEOP with Cesium Vapor CsH and CsF

Cesium Fluoride

There is little published data on CsF relaxation times

19F and 1H have similar gyromagnetic ratios

The same probe and spectrometer electronics can be used

Both 19F and 1H are spin - 1/2

We expect similar relaxation mechanisms, hence similar T1 We also expect T1 for 133Cs to be the same

CsCl crystal structure above 300 K, otherwise NaCl crystal structure Other cesium salts have CsCl crystal structure

Ben Andrew Olsen High-Field SEOP of Cesium Salts

Spin Exchange Optical Pumping Experimental Setup Results Optical Pumping Setup High-Frequency NMR Probe

Optical Pumping Setup

Chopper Alkali Cell NMR400 Shutter

Photodiode Polarizing Beam Splitter λ/4 Plate Fiber Coupler Multi-mode Fiber

PC

NMR Spectrometer

Diode Pump Laser Ti:Sapphire Laser

02.30 05.10

Lock-In Amplifier

335 290.1 GHz

Wavemeter

Single-Mode Fiber

Figure from B. Patton, Ph.D. Thesis, Princeton University, Sep. 2007 Ben Andrew Olsen High-Field SEOP of Cesium Salts

Spin Exchange Optical Pumping Experimental Setup Results Optical Pumping Setup High-Frequency NMR Probe

High-Frequency NMR Probe

Inductive coil for producing tipping pulses and detecting sample polarization Variable capacitors for adjusting resonant response Holds vapor cell steadily in beam path Electrically isolated from probe cap Ideally hydrogen-free

Coil made completely of bare copper

Ben Andrew Olsen High-Field SEOP of Cesium Salts

Spin Exchange Optical Pumping Experimental Setup Results Optical Pumping Setup High-Frequency NMR Probe

High-Frequency NMR Probe

Ben Andrew Olsen High-Field SEOP of Cesium Salts

Spin Exchange Optical Pumping Experimental Setup Results Cesium Fluoride Cesium Hydride

T1 Measurements in CsF

Green data points from D. K. Hutchins and S. M. Day, Phys. Rev., 180(2), Apr 1969 Ben Andrew Olsen High-Field SEOP of Cesium Salts

Spin Exchange Optical Pumping Experimental Setup Results Cesium Fluoride Cesium Hydride

Cs NMR Enhancement in CsH

Ben Andrew Olsen High-Field SEOP of Cesium Salts

Spin Exchange Optical Pumping Experimental Setup Results Cesium Fluoride Cesium Hydride

1H NMR

Large background signal

Shorter T1 (∼ 100 s) Narrow spectral feature

Spectral feature from H in CsH is very broad T1 is very long, so we can’t average as much

Ben Andrew Olsen High-Field SEOP of Cesium Salts

Spin Exchange Optical Pumping Experimental Setup Results Cesium Fluoride Cesium Hydride

1H NMR Subtraction Averaging

Ben Andrew Olsen High-Field SEOP of Cesium Salts

Spin Exchange Optical Pumping Experimental Setup Results Cesium Fluoride Cesium Hydride

1H NMR Enhancement

Ben Andrew Olsen High-Field SEOP of Cesium Salts

Spin Exchange Optical Pumping Experimental Setup Results Conclusions

Conclusions

CsF is a poor candidate for SEOP

T1 for 19F is short CsF is very difficult to deal with

Heteronuclear SEOP is possible in CsH

Enhancement is small Background subtraction is imperfect

Electron and nuclear spin currents are comparable in homonuclear SEOP

Dependence of angular momentum currents on photon polarization is not well understood

Ben Andrew Olsen High-Field SEOP of Cesium Salts