Amplitude-modulated Magneto-Optical Rotation in Paraffin-coated Cells and Buffer Gas Cells

AMOR in paraffin-coated and buffer gas cells

Amplitude-modulated magneto-opticalrotation in paraffin-coated cells

and buffer gas cells

B.K. Park, A. Family, S. Pustelny, K. Brzozowski, V. Acosta,D. Budker, and W. Gawlik

Joint Kraków-Berkeley Atomic Physics and Photonics Laboratory

Oct. 18, 2008


Outline

1 introduction

2 experimental setup

3 resultssample signalsfwhm and sensitivity, modus operandifwhm and sensitivity, results

4 discussion and comparisonoptimization parametersdetuning spectrum

5 miscellany


introduction

AMOR technique

synchronous pumping with linearly-polarized light


introduction

atomic magnetometer sensitivity

fundamental sensitivity limit:

δB ≈ 1gµ

~√NτT

(1)

g: ground state gyromagnetic ratioN: number of atomsτ : spin-relaxation timeT : measurement time


introduction

in the paraffin-coated cell ...

spin coherences preservedthrough 1000s of coated wallcollisionsproperties of paraffin limitsexperimental parameters

starts melting at around40◦Cirreversible damages to thecoating at about 80◦C


introduction

in the buffer gas cell ...

atoms diffuse through thebuffer gas, increasing theinteraction time

τ = R2/6D, D ∝ 1/nBG

collisions with buffer gas⇒broadening of absorption linehigher sensitivity to magneticfield gradients


introduction

objectives

compare sensitivity of buffer gas cells to that ofparaffin-coated cell for atomic magnetometryfind optimization parameters for buffer gas cells

buffer gas densitytemperaturelight power


experimental setup

schematic diagram for AMOR measurements


experimental setup

shields and coils


experimental setup

the oven


results

sample signals

sample signals

-3-2.5

-2-1.5

-1-0.5

0 0.5

1 1.5

30.4 30.6 30.8 31 31.2

sign

al (

rad)

frequency (kHz)

paraffin-coated cell

-5

-4

-3

-2

-1

0

1

2

3

27 28 29 30 31 32 33 34 35

sign

al (

rad)

frequency (kHz)

3-torr buffer gas cell

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

53.5 54 54.5 55 55.5 56 56.5

sign

al (

rad)

frequency (kHz)


-0.25-0.2

-0.15-0.1

-0.05 0

0.05 0.1

0.15 0.2

0.25

53.5 54 54.5 55 55.5 56 56.5

sign

al (

rad)

frequency (kHz)



results

fwhm and sensitivity, modus operandi

power-dependence measurement

0

20

40

60

80

100

120

140

160

0 5 10 15 20 25 30 35 40

FW

HM

(H

z)

pump power (µW)

FWHM at various powers in paraffin-coated cell, 55°C

intercepts: 45.3(4), 53.7(5), 63.9(5), 72.9(5)slopes: 1.895(17), 1.902(21), 1.890(20), 1.870(23)

probe = 5 µW probe = 10 µW probe = 15 µW probe = 20 µW


results

fwhm and sensitivity, modus operandi

sensitivity dependence on power

100

0 5 10 15 20 25 30 35 40

proj

ecte

d se

nsiti

vity

(nG

/√H

z)

pump power (µW)

projected sensitivity in paraffin-coated cell, 55°C

probe = 5 µW probe = 10 µW probe = 15 µW probe = 20 µW


results

fwhm and sensitivity, results

best results, overall

best widthswith paraffin-coated cell: 12 Hz @ 30◦Cwith buffer gas cell: 27 Hz @ 38◦C in 30-torr cell

best sensitivitywith paraffin-coated cell: 1.5 nG/

√Hz @ 55◦C

with buffer gas cell: 8 nG/√

Hz @ 65◦C in 3-torr and30-torr cellcf. fundamental sensitivity limit from Eq. 1 (T = 70◦C andτ = 1/(2π × 100 Hz):

δB = 4× 10−11 G/√

Hz


discussion and comparison

optimization parameters

Detuning spectrum for 300-torr cell

-0.00012

-0.0001

-8e-05

-6e-05

-4e-05

-2e-05

0

-6000 -4000 -2000 0 2000 4000 6000 0

0.2

0.4

0.6

0.8

1

rota

tion

(rad

)

tran

smis

sion

(re

l. fr

actio

n)

laser detuning from PL[2,1] (MHz)

absorption and detuning in 300-torr buffer gas cell at 70°C, probe = 5 µW, pump = 40 µW

absorption rotation reference




Temperature dependence in 100-torr cell

0

50

100

150

200

250

30 40 50 60 70 80 90 0

200

400

600

800

1000

1200

1400

1600

1800

FW

HM

(H

z)

sens

itivi

ty (

nG/√

)

Oven temperature (°C)

Power-broadening-free FWHM and sensitivity FoM at various temperatures in 100 torr cell

FWHM sensitivity




FWHM vs. buffer gas density

0

50

100

150

200

250

300

350

400

450

1e+17 1e+18 1e+19

FW

HM

(H

z)

buffer gas density (cm-3)

FWHM at about 70°C in all buffer gas cells



detuning spectrum

detuning spectrum for all buffer gas cells

-0.06

-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

-4000 -3000 -2000 -1000 0 1000 2000 3000 4000

rota

tion

(rad

)


detuning spectrum in all buffer gas cells at about 70°C, probe = 5 µW, pump = 40 µW

rotation in 3-torr cellrotation in 30-torr cell

rotation in 100-torr cell

rotation in 300-torr cellreference



detuning spectrum

detuning spectrum around zero

-0.0004

-0.0002

0

0.0002

0.0004

-4000 -3000 -2000 -1000 0 1000 2000 3000 4000

rota

tion

(rad

)


detuning spectrum in all buffer gas cells at about 70°C, probe = 5 µW, pump = 40 µW,closer around zero

rotation in 3-torr cellrotation in 30-torr cell

rotation in 100-torr cell

rotation in 300-torr cellreference


miscellany

collaborators on the project


miscellany

magnetic-field-dependent sensitivity to duty cycle

0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

0.0014

0 20 40 60 80 100 37.5

38

38.5

39

39.5

40

40.5

41

41.5

42

Res

onan

ce p

eak

(rad

)

Res

onan

ce w

idth

(H

z)

Duty cycle (%)

Amplitude- and Width-dependence on duty cycle, square wavepump power = 19 µW, probe power = 5 µW, modulated at 400 mV (full depth), near 885 Hz

AmplitudeFWHM


miscellany


0

0.0001

0.0002

0.0003

0.0004

0.0005

0.0006

0.0007

0 20 40 60 80 100 37.5

38

38.5

39

39.5

40

40.5

41

41.5

42

Res

onan

ce p

eak

(rad

)

Res

onan

ce w

idth

(H

z)

Duty cycle (%)

Amplitude- and Width-dependence on duty cycle, square wavepump power = 19 µW, probe power = 5 µW, modulated at 400 mV (full depth), near 29.7 kHz

AmplitudeFWHM


miscellany


0

0.0001

0.0002

0.0003

0.0004

0.0005

0.0006

0.0007

0 20 40 60 80 100 25

30

35

40

45

50

55

60

Res

onan

ce p

eak

(rad

)

Res

onan

ce w

idth

(H

z)

Duty cycle (%)

Amplitude- and Width-dependence on duty cycle, square wavepump power = 19 µW, probe power = 5 µW, modulated at 400 mV (full depth), near 146.4 kHz

AmplitudeFWHM


miscellany

giving 250%


miscellany

giving 250%

0

0.1

0.2

0.3

0.4

0.5

0.6

0.08 0.0805 0.081 0.0815 0.082 0.0825 0.083 0.0835 0.084 0.0845

inte

nsity

(ar

b. u

nits

)

time (s)

light modulated with sine at 1000 mV

Amplitude-modulated Magneto-Optical Rotation in Paraffin-coated Cells and Buffer Gas Cells

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Transcript of Amplitude-modulated Magneto-Optical Rotation in Paraffin-coated Cells and Buffer Gas Cells