3He Polarization Tests at UIUC

Danielle ChandlerDavid Howell

UIUC

Overview

• Confirmation of successful 3He polarization using 1083-nm optical signal

• Use of optical signal to calibrate perturbing field (B1)

• NMR setup and initial tests

Tests using optical signalcell

light detector

cell

Confirmation of 3He Polarization

Baseline drops on the 1083-nm light signal when B0 is turned on

1083-nm light produced in cell decreases when 3He is polarized because polarized atoms do not interact with the circularly-polarized laser light

Response of optical signal to continuous oscillatory B1 field

20

2

10

)γ/ωB(B

BA)ωA(

1

Scanned through the B1 resonance frequency and recorded the optical signal

At resonance, the perturbing field rotates the 3He spins away from the B0 axis, which makes the optical pumping more efficient… therefore there is a peak in the optical signal at resonance.

Results of B1 frequency scans

3 1Peak width 2 3 γ B2

02

1

)γ/ωB(B

BheightPeak

1

1

0

1

peak height is independent of B

on resonance, B ω/ 0, or for

sufficiently large B

Non-zero width as B0 → 0 reflectsnonuniformity in B0/B1 fields

B1 dependence suggests B0/B1 nonuniformity

Response of optical signal as a function of time

Amplitude of oscillation damps out as cell becomes depolarized

Signal decays as laser light repolarizes the 3He cell

end of pulse

Optical signal peaks when the pulse time gives a π pulse, since this should orient the spins antiparallel to the B0 axis, making optical pumping maximally efficient

Using optical signal to calibrate π/2 burst pulse

4

T timepulse

2

π

First maximum corresponds to π pulse

T

B1 program voltage = 2.5 Vpp

For a given B1:

Can use this optical method to calibrate B1:

γT

2π

(T/4)2γ

πB1

NMR Measurement Setup

Adiabatic fast passage method

Free induction decay method

NMR Measurements

With current setup, we observe the sensitivity to detect NMR signal at a level of 0.2 μV

Need to improve the design of the NMR for a better signal/noise ratio

Calculate that NMR signal should be of the same order of magnitude

Response of NMR coil to B1 pulse burst

Conclusion

Optical signal tests were successful and provide a method of calibrating B1

Preparing to make improvements on NMR sensitivity

(for example)increase number of turns on pickup coilsoptimize position and geometry of coilsoptimize Q-factorintroduce second pair of pickup coils