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http://www.umich.edu/aehardt

Developing a Portable Optical

Frequency Standard

with Atomic Mercury

K.R. Moore†, E.A. Alden*, A.E. Leanhardt* Leanhardt Lab

†Applied Physics Program, University of Michigan

*Physics Department, University of Michigan

June 6, 2012 DAMOP XLIII, Anaheim CA


Overview


• Hg frequency standard for a hot optical clock

• Limiting broadening mechanism contributing

to fractional frequency uncertainty

• Schemes for detecting population in clock state


Frequency Standards


Δν: Linewidth of system

ν: Frequency of sampling probe

T: Duty cycle of experiment

τ: Total experiment time

N: Sample size per duty cycle

•* denotes theorized values not experimentally realized

•References available

• Fractional frequency uncertainty:


Frequency Standard with Atomic Hg


[1] Calculated, natural abundance: A.P.

Mishra and T.K. Balasubramamian.

JQSRT 69, 769 - 780 (2001)

τ =5.78s [1]

3P0

3P1

1S0 531nm

531nm Δν: Linewidth of system















[1] Calculated, natural abundance: A.P.

Mishra and T.K. Balasubramamian.

JQSRT 69, 769 - 780 (2001)

τ =5.78s [1]

3P0

3P1

1S0 531nm

531nm










Hg atoms

Laser

E

E

• Eliminate first-order Doppler

broadening of the linewidth


• Limitations due to portability:

Broadening: Collisions

Broadening: Laser power amplification


System Portability

• Portability:

Vapor cell atomic source:

Solid-state compact laser:

60. Col kHz

?. Las

Cell temperature: 60ºC


Laser Characterization

Seed Laser:

20 mW

1062 nm

Δν = 914 Hz*

Amplifier:

50 W

1062 nm

Δν ≤ ?


*measured by

Orbits Lightwave

SHG:

6 W

531 nm

Δν2 212 input



Seed Laser:

20 mW

1062 nm

Δν = 914 Hz*

Amplifier:

50 W

1062 nm

Δν ≤ ?


*measured by

Orbitz Lightwave

SHG:

6 W

531 nm

Δν2 212 input



From Seed

Beat Note:

1MHz

• Shifting the laser frequency in a Mach-Zender interferometer results in a

beat note centered at a down-converted frequency.


AOM

AOM



From Seed


AOM

AOM






Hz

His

t. C

ou

nts

Linewidth:

12.1±6.1Hz

• A delay line is required to verify the actual linewidth.

• The relative broadening between the seed-seed beat note and the seed-

amplified beat note can be measured to some limit.

• Beat note, example data set:

Beat

Seed

with

Seed:



From Seed

Beat Note:

1MHz


AOM

AOM

• In place of the amplifier, external noise is artificially applied to one arm

of the interferometer.



From Seed

Beat Note:

1MHz Artificial

Noise

• In place of the amplifier, external noise is artificially applied to one arm

of the interferometer.


AOM

AOM


kHz

Am

pl.

(a.

u.)

kHz

Am

pl.

(a.

u.)



Linewidth:

12.1±6.1Hz

Beat

Seed

with

Artificial

Noise (50mV):


Beat

Seed

with

Seed:

Linewidth:

2.7±0.5kHz



From Seed

Beat Note:

1MHz Artificial

Noise


AOM

AOM





From Seed

Beat Note:

1MHz




AOM

AOM



From Seed

Beat Note:

1MHz

AOM

AOM

Amplifier





kHz

Am

pl.

(a.

u.)

kHz

Am

pl.

(a.

u.)



Beat

Seed

with

Amplified

Light (14.2W):


Beat

Seed

with

Seed:

Linewidth:

12.1±6.1Hz

Linewidth:

7.2±3.6Hz




• After replacing the amplifier in the system, measurements show no

systematic change in the linewidth of the beat note.

ΔL

inew

idth

[H

z]

IR Power [W]

• Increasing amplifier power:

http://www.umich.edu/aehardt June 6, 2012 DAMOP XLIII, Anaheim CA

Broadening Mechanisms

• Theorized values for other broadening mechanisms:

Cell temperature: 60ºC | Spot size: 500 μm | Green power: 6 W





Duty Cycle: 1/T < 0.1 Hz | Number of interacting atoms: N ≈ 6×1012





Duty Cycle: 1/T < 0.1 Hz | Number of interacting atoms: N ≈ 6×1012

2/11610


Proof-of-Principle Outlook

• Detect population in

the 3P0 level using:

• Known cascade with

NH3 buffer gas[1]

• Excite to the 3S1 level

with 405nm, detect

radiative decay[2]


[1] C.G. Freeman, M.J. McEwan, R.F.C. Claridge and L.F. Phillips.

Trans. Faraday Soc., 1971,67, 2004-2008

[2] E. C. Benck, J. E. Lawler and J. T. Dakin. JOSAB 6, 11 (1989)

63P0

61S0

531nm

531nm

63P2

61P1

63P1

73S1

405nm


Summary

• Compact, solid-state set-up for an optical clock

• Limited by collisional broadening, which

could lead to a fractional frequency stability of

σν ≈ 10-16 ×√τ.

• Outlook for detecting population



Acknowledgements


Aaron

Leanhardt

Skyler

Degenkolb Yisa

Rumala

Jeongwon

Lee Emily

Alden Kaitlin

Moore

• Funding:

DARPA/ARO

• Dept. of Physics,

University of

Michigan

• Applied Physics

Program, Univ-

ersity of Michigan

Tim

Chupp


Standards References


[1]

[2]

[3]

[4]

[5]

[6]

[7]

[8]

[9]

[10]

[11]

D. McKenna, C. Tanner. Progress toward a two-photon optical atomic clock in neutral

silver. Abstract submitted for the DAMOP12 Meeting of APS (K1.00140), January 2012.

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