Abstract

We present encouraging results obtained with an experimental apparatus based on coherent population trapping and aimed at detecting a biological (cardiac) magnetic field in a magnetically compensated but unshielded volume. The work includes magnetic-field and magnetic-field-gradient compensation and uses differential detection to cancel common mode magnetic noise. Synchronous data acquisition with a reference (electrocardiographic or pulse-oximetric) signal makes possible improvement of the signal-to-noise ratio in off-line averaging. The setup has the significant advantages of working at room temperature with a small-size head, and the possibility of fast adjustments of the dc bias magnetic field, which makes the sensor suitable for detecting a biomagnetic signal at any orientation with respect to the axis of the head and in any position on the patient’s chest, which is not the case with other kinds of magnetometers.

© 2007 Optical Society of America

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References

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2007 (2)

2006 (3)

S. Groeger, G. Bison, J.-L. Schenker, R. Wynands, and A. Weis, "A high-sensitivity laser-pumped Mx magnetometer," Eur. Phys. J. D 38, 239-247 (2006).
[CrossRef]

H. Xia, A. Ben-Amar Baranga, D. Hoffman, and M. V. Romalis, "Magnetoencephalography with an atomic magnetometer," Appl. Phys. Lett. 89, 211104 (2006).
[CrossRef]

V. Acosta, M. P. Ledbetter, S. M. Rochester, and D. Budker, "Nonlinear magneto-optical rotation with frequency-modulated light in the geophysical field range," Phys. Rev. A 73, 053404 (2006).
[CrossRef]

2004 (1)

S. J. Seltzer and M. Romalis, "Unshielded three axis vector operation of a spin-exchange-relaxation-free atomic magnetometer," Appl. Phys. Lett. 85, 4804-4806 (2004).
[CrossRef]

2003 (3)

C. Andreeva, G. Bevilacqua, V. Biancalana, S. Cartaleva. Y. Dancheva, T. Karaulanov, C. Marinelli, E. Mariotti, and L. Moi, "Two-color coherent population trapping in a single Cs hyperfine transition, with application in magnetometry," Appl. Phys. B 76, 667-675 (2003).
[CrossRef]

G. Bison, R. Wynands, and A. Weis, "A laser-pumped magnetometer for the mapping of human cardiomagnetic fields," Appl. Phys. B 76, 325-328 (2003).
[CrossRef]

G. Bison, R. Wynands, and A. Weis, "Dynamical mapping of the human cardiomagnetic field with a room-temperature, laser-optical sensor," Opt. Express 11, 904-909 (2003).
[CrossRef] [PubMed]

2002 (4)

C. Affolderbach, M. Stahler, S. Knappe, and R. Wynands, "An all-optical, high-sensitivity magnetic gradiometer," Appl. Phys. B 75, 605-612 (2002).
[CrossRef]

D. Budker, W. Gawlik, D. F. Kimball. M. Rochester, V. V. Yashchuk, and A. Weis, "Resonant nonlinear magneto-optical effect in atoms," Rev. Mod. Phys. 74, 1154-1210 (2002).
[CrossRef]

J. Allred, R. Lyman, T. Kornack, and M. Romalis, "A high-sensitivity atomic magnetometer unaffected by spin-exchange relaxation," Phys. Rev. Lett. 89, 130801 (2002).
[CrossRef] [PubMed]

D. Budker, D. F. Kimball, V. V. Yashchuk, and M. Zolotorev, "Nonlinear magneto-optical rotation with frequency-modulated light," Phys. Rev. A 65, 055403 (2002).
[CrossRef]

1999 (1)

R. Wynands and A. Nagel, "Precision spectroscopy with coherent dark states," Appl. Phys. B 68, 1-25 (1999).
[CrossRef]

1969 (1)

J. Dupont-Roc, S. Haroche, and C. Cohen-Tannoudji, "Detection of very weak magnetic fields (10−9 gauss) by 87Rb-zero-field level crossing resonances," Phys. Lett. 28A, 638-639 (1969).
[CrossRef]

1962 (1)

Appl. Opt. (1)

Appl. Phys. B (4)

C. Affolderbach, M. Stahler, S. Knappe, and R. Wynands, "An all-optical, high-sensitivity magnetic gradiometer," Appl. Phys. B 75, 605-612 (2002).
[CrossRef]

G. Bison, R. Wynands, and A. Weis, "A laser-pumped magnetometer for the mapping of human cardiomagnetic fields," Appl. Phys. B 76, 325-328 (2003).
[CrossRef]

C. Andreeva, G. Bevilacqua, V. Biancalana, S. Cartaleva. Y. Dancheva, T. Karaulanov, C. Marinelli, E. Mariotti, and L. Moi, "Two-color coherent population trapping in a single Cs hyperfine transition, with application in magnetometry," Appl. Phys. B 76, 667-675 (2003).
[CrossRef]

R. Wynands and A. Nagel, "Precision spectroscopy with coherent dark states," Appl. Phys. B 68, 1-25 (1999).
[CrossRef]

Appl. Phys. Lett. (2)

H. Xia, A. Ben-Amar Baranga, D. Hoffman, and M. V. Romalis, "Magnetoencephalography with an atomic magnetometer," Appl. Phys. Lett. 89, 211104 (2006).
[CrossRef]

S. J. Seltzer and M. Romalis, "Unshielded three axis vector operation of a spin-exchange-relaxation-free atomic magnetometer," Appl. Phys. Lett. 85, 4804-4806 (2004).
[CrossRef]

Eur. Phys. J. D (1)

S. Groeger, G. Bison, J.-L. Schenker, R. Wynands, and A. Weis, "A high-sensitivity laser-pumped Mx magnetometer," Eur. Phys. J. D 38, 239-247 (2006).
[CrossRef]

J. Opt. Soc. Am. B (1)

Nature (1)

D. Budker and M. Romalis, "Optical magnetometry," Nature 3, 227-234 (2007).

Opt. Express (1)

Phys. Lett. (1)

J. Dupont-Roc, S. Haroche, and C. Cohen-Tannoudji, "Detection of very weak magnetic fields (10−9 gauss) by 87Rb-zero-field level crossing resonances," Phys. Lett. 28A, 638-639 (1969).
[CrossRef]

Phys. Rev. A (2)

D. Budker, D. F. Kimball, V. V. Yashchuk, and M. Zolotorev, "Nonlinear magneto-optical rotation with frequency-modulated light," Phys. Rev. A 65, 055403 (2002).
[CrossRef]

V. Acosta, M. P. Ledbetter, S. M. Rochester, and D. Budker, "Nonlinear magneto-optical rotation with frequency-modulated light in the geophysical field range," Phys. Rev. A 73, 053404 (2006).
[CrossRef]

Phys. Rev. Lett. (1)

J. Allred, R. Lyman, T. Kornack, and M. Romalis, "A high-sensitivity atomic magnetometer unaffected by spin-exchange relaxation," Phys. Rev. Lett. 89, 130801 (2002).
[CrossRef] [PubMed]

Rev. Mod. Phys. (1)

D. Budker, W. Gawlik, D. F. Kimball. M. Rochester, V. V. Yashchuk, and A. Weis, "Resonant nonlinear magneto-optical effect in atoms," Rev. Mod. Phys. 74, 1154-1210 (2002).
[CrossRef]

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Figures (5)

Fig. 1
Fig. 1

Experimental setup. PMOF, polarization maintaining optical fiber; CL, collimating lens; IBS, intensity beam splitter; NF, neutral filters; PD, photodiode.

Fig. 2
Fig. 2

Schematics of the apparatus. The selected component of the background bias field B 0 , parallel to z ̂ in the scheme, determines the direction of the detected component of the biosignal, while laser beams separated by Δ are directed along x ̂ .

Fig. 3
Fig. 3

CPT line shapes produced with circular polarization and magnetic field orientation orthogonal to the laser beam (along the z ̂ direction). Circles: static gradients are not compensated. Fitted linewidth is 1.67 kHz . Squares: optimized compensation of the gradient components. Fitted linewidth is reduced to 280 Hz .

Fig. 4
Fig. 4

(a) Single input acquisition: laser frequency is tuned to the center of the CPT resonance. (b) Differential input acquisition: CPT resonances on the two arms of the sensor are separated by more than their linewidth. In these first two traces the 50 Hz peak maximum value is 2.2 nT Hz (in the z ̂ direction), which is out of the range presented in the graph. (c) Differential input acquisition: the overlapping of CPT resonances is optimized. (d) Out of Doppler absorption resonance noise in differential input mode. (e) Out of Doppler absorption resonance noise in single input mode. In the inset the total rms noise N integrated between 1 and 30 Hz (cardiosignal bandwidth) relative to each trace is reported.

Fig. 5
Fig. 5

Reconstructed cardiac pulse. The signal is averaged over a set of 150 cardiac pulses acquired at a 128 Hz sampling rate. The lock-in equivalent noise bandwidth is 41.7 Hz .

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