A Rubidium Spin Filter -

Prototype and Prospects for a Turnkey Source of Polarized Electrons

Perpetrators

UNL

Levi NeukirchAdam GreenBrooks HittMark RosenberryHerman BatelaanTJG

LANL

Dale Tupa

He direct extraction source

McCusker, Hatfield and Walters, PRA 5, 177 (1972)

Rolla Source Results

The Good News: 50μA of current (@ 3% polarization)

The Bad News: Stringent requirement for high percentage of discharge in excited states; ΔE ~ 6 eV

Improvements: LMA laser; side-

pi pumping

Answer: use ground state atoms

e-

+ Rb

→ e-

+ Rb

Fabrikant

and Thumm, JPB 40, 1245 (1999)

Require (at 5 eV) that σex

nRb

ℓ

~ 1 →

nRb

~ 1014

cm-3

Other (Electron) Spin Filters

Ann.Phys. 2, 465 (1993)

See also work on neutron spin filters by Gentile, Chupp, Cates etc…

An early spin-exchange source

Krisciokaitis-Krist

and Tsai, NIM 83, 45 (1970)

Chanin

et alii, PR 80, 67 (1962)

N2 pressure (Torr)1.0e-4 1.0e-3 1.0e-2 1.0e-1

0.01

0.10

1.00

B-field (T)0.000 0.005 0.010 0.015 0.020 0.025

0.0

0.0

0.2

0.3

0.4

0.5

0.6Tr

ansm

issi

onPo

lariz

atio

nTr

ansm

issi

onPo

lariz

atio

n

Some model calculations for nRB

= 3 x 1014

cm-3

Rb

optical pumping

σ+

5P1/2

= 795nm

F = 1

λ

5S1/2

F = 2

+σ

F = 1

F = 2

λ = 78

0nm

5P3/2

F = 0

F = 2F = 1

F = 3

pumpprobe

Rb optical pumping and radiation trapping

rogue photons

collisional

quenching

One solution: Gausses

1012

Tupa

et al., PRA 33, 1045 (1986); 36, 2142 (1987)

rogue photons

collisional

quenching

vibrational

quenching

Another Solution: Add Buffer Gas

Rb optical pumping with N2

First attempt

1 mm APERTURE

ELECTRON OPTICS

CATHODE

+σ

ANODE

N2 INLET

Rb

POLARIMETERNe OPTICAL

B

LC

e-

spin filter(OPESF)

Ar

+

laserDye laser

DiodeLaser

Optical Polarimeter

Reference cell

Pump beam

Photodetector

Photodetector

Magnetic coillenses

λ /4-plate

mirror

beamsplitter

Probe beam

Analyzer

polarizerPolarizer +

Probe data

Bln

BRb μλ

δφπ2

2)(8ΓΔ

=

23)(56λδφπ

ΓΔ

=ln

PRb

Rb

• ΔΦ

= optical rotation of probe

• δ

= probe beam detuning

• l = path length

• λ

= D2 wavelength

• Γ

= D2 natural width

Results

Batelaan

et alii, PRL 82, 4216 (1999)

Figure of Merit = P2I = 0.28 μA

¡Nitrogen - the wonder buffer!

•

provides the electrons•

narrows their energy spread

•

thermalization

increases σex

•

increases path length, l•

vibrational

quenching

•

diffusion barrier•

broadens absorption profile

v.2

Problem

Pump beam is most efficient at entrancepoint, where the electrons that will ultimatelybe polarized aren’t.

High magnetic field side-pumping scheme

Martin, Walker, Anderson, and Swenson, NIM A 335, 233 (1993)

Rb absorption vs. B-field

Side-pumping geometry

Possibilities for the future

T. Walker et al.