Abstract

We have developed a four-channel optically pumped atomic magnetometer for magnetoencephalography (MEG) that incorporates a passive diffractive optical element (DOE). The DOE allows us to achieve a long, 18-mm gradiometer baseline in a compact footprint on the head. Using gradiometry, the sensitivities of the channels are < 5 fT/Hz1/2, and the 3-dB bandwidths are approximately 90 Hz, which are both sufficient to perform MEG. Additionally, the channels are highly uniform, which offers the possibility of employing standard MEG post-processing techniques. This module will serve as a building block of an array for magnetic source localization.

© 2016 Optical Society of America

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References

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    [Crossref] [PubMed]
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  22. I. K. Kominis, T. W. Kornack, J. C. Allred, and M. V. Romalis, “A subfemtotesla multichannel atomic magnetometer,” Nature 422(6932), 596–599 (2003).
    [Crossref] [PubMed]
  23. H. Xia, A. Ben-Amar Baranga, D. Hoffman, and M. V. Romalis, “Magnetoencephalography with an atomic magnetometer,” Appl. Phys. Lett. 89(21), 211104 (2006).
    [Crossref]
  24. M. P. Ledbetter, I. M. Savukov, V. M. Acosta, D. Budker, and M. V. Romalis, “Spin-exchange-relaxation-free magnetometry with Cs vapor,” Phys. Rev. A 77(3), 033408 (2008).
    [Crossref]
  25. H. B. Dang, A. C. Maloof, and M. V. Romalis, “Ultrahigh sensitivity magnetic field and magnetization measurements with an atomic magnetometer,” Appl. Phys. Lett. 97(15), 151110 (2010).
    [Crossref]
  26. K. Kim, S. Begus, H. Xia, S. K. Lee, V. Jazbinsek, Z. Trontelj, and M. V. Romalis, “Multi-channel atomic magnetometer for magnetoencephalography: a configuration study,” Neuroimage 89, 143–151 (2014).
    [Crossref] [PubMed]
  27. C. Johnson, P. D. D. Schwindt, and M. Weisend, “Magnetoencephalography with a two-color pump-probe, fiber-coupled atomic magnetometer,” Appl. Phys. Lett. 97(24), 243703 (2010).
    [Crossref]
  28. C. Johnson and P. D. D. Schwindt, “A two-color pump probe atomic magnetometer for magnetoencephalography,” Proc. IEEE Int. Freq. Cont., 371–375 (2010).
    [Crossref]
  29. C. N. Johnson, P. D. D. Schwindt, and M. Weisend, “Multi-sensor magnetoencephalography with atomic magnetometers,” Phys. Med. Biol. 58(17), 6065–6077 (2013).
    [Crossref] [PubMed]
  30. T. H. Sander, J. Preusser, R. Mhaskar, J. Kitching, L. Trahms, and S. Knappe, “Magnetoencephalography with a chip-scale atomic magnetometer,” Biomed. Opt. Express 3(5), 981–990 (2012).
    [Crossref] [PubMed]
  31. O. Alem, A. M. Benison, D. S. Barth, J. Kitching, and S. Knappe, “Magnetoencephalography of epilepsy with a microfabricated atomic magnetrode,” J. Neurosci. 34(43), 14324–14327 (2014).
    [Crossref] [PubMed]
  32. N. Mizutani, K. Okano, K. Ban, S. Ichihara, A. Terao, and T. Kobayashi, “A plateau in the sensitivity of a compact optically pumped atomic magnetometer,” AIP Adv. 4(5), 057132 (2014).
    [Crossref]
  33. M. A. Uusitalo and R. J. Ilmoniemi, “Signal-space projection method for separating MEG or EEG into components,” Med. Biol. Eng. Comput. 35(2), 135–140 (1997).
    [Crossref] [PubMed]
  34. S. Taulu, M. Kajola, and J. Simola, “Suppression of Interference and Artifacts by the Signal Space Separation Method,” Brain Topogr. 16(4), 269–275 (2004).
    [Crossref] [PubMed]
  35. I. M. Savukov and M. V. Romalis, “Effects of spin-exchange collisions in a high-density alkali-metal vapor in low magnetic fields,” Phys. Rev. A 71(2), 023405 (2005).
    [Crossref]
  36. M. A. Rosenberry, J. P. Reyes, D. Tupa, and T. J. Gay, “Radiation trapping in rubidium optical pumping at low buffer-gas pressures,” Phys. Rev. A 75(2), 023401 (2007).
    [Crossref]
  37. C. Cohen-Tannoudji and J. Dupont-Roc, “Experimental study of Zeeman light shifts in weak magnetic fields,” Phys. Rev. A 5(2), 968–984 (1972).
    [Crossref]
  38. M. Rosatzin, D. Suter, and J. Mlynek, “Light-shift-induced spin echoes in a J=1/2 atomic ground state,” Phys. Rev. A 42(3), 1839–1841 (1990).
    [Crossref] [PubMed]
  39. F. Gong, Y. Y. Jau, and W. Happer, “Magnetic resonance reversals in optically pumped alkali-metal vapor,” Phys. Rev. A 75(5), 053415 (2007).
    [Crossref]
  40. S. Appelt, A. B.-A. Baranga, C. J. Erickson, M. V. Romalis, A. R. Young, and W. Happer, “Theory of spin-exchange optical pumping of 3He and 129Xe,” Phys. Rev. A 58(2), 1412–1439 (1998).
    [Crossref]
  41. B. Chann, E. Babcock, L. W. Anderson, and T. G. Walker, “Skew light propagation in optically thick optical pumping cells,” Phys. Rev. A 66(3), 033406 (2002).
    [Crossref]
  42. T. W. Kornack, S. J. Smullin, S. K. Lee, and M. V. Romalis, “A low-noise ferrite magnetic shield,” Appl. Phys. Lett. 90(22), 223501 (2007).
    [Crossref]

2015 (1)

O. Alem, T. H. Sander, R. Mhaskar, J. LeBlanc, H. Eswaran, U. Steinhoff, Y. Okada, J. Kitching, L. Trahms, and S. Knappe, “Fetal magnetocardiography measurements with an array of microfabricated optically pumped magnetometers,” Phys. Med. Biol. 60(12), 4797–4811 (2015).
[Crossref] [PubMed]

2014 (4)

K. Kim, S. Begus, H. Xia, S. K. Lee, V. Jazbinsek, Z. Trontelj, and M. V. Romalis, “Multi-channel atomic magnetometer for magnetoencephalography: a configuration study,” Neuroimage 89, 143–151 (2014).
[Crossref] [PubMed]

O. Alem, A. M. Benison, D. S. Barth, J. Kitching, and S. Knappe, “Magnetoencephalography of epilepsy with a microfabricated atomic magnetrode,” J. Neurosci. 34(43), 14324–14327 (2014).
[Crossref] [PubMed]

N. Mizutani, K. Okano, K. Ban, S. Ichihara, A. Terao, and T. Kobayashi, “A plateau in the sensitivity of a compact optically pumped atomic magnetometer,” AIP Adv. 4(5), 057132 (2014).
[Crossref]

G. Lembke, S. N. Erné, H. Nowak, B. Menhorn, A. Pasquarelli, and G. Bison, “Optical multichannel room temperature magnetic field imaging system for clinical application,” Biomed. Opt. Express 5(3), 876–881 (2014).
[Crossref] [PubMed]

2013 (2)

V. K. Shah and R. T. Wakai, “A compact, high performance atomic magnetometer for biomedical applications,” Phys. Med. Biol. 58(22), 8153–8161 (2013).
[Crossref] [PubMed]

C. N. Johnson, P. D. D. Schwindt, and M. Weisend, “Multi-sensor magnetoencephalography with atomic magnetometers,” Phys. Med. Biol. 58(17), 6065–6077 (2013).
[Crossref] [PubMed]

2012 (4)

T. H. Sander, J. Preusser, R. Mhaskar, J. Kitching, L. Trahms, and S. Knappe, “Magnetoencephalography with a chip-scale atomic magnetometer,” Biomed. Opt. Express 3(5), 981–990 (2012).
[Crossref] [PubMed]

R. Wyllie, M. Kauer, R. T. Wakai, and T. G. Walker, “Optical magnetometer array for fetal magnetocardiography,” Opt. Lett. 37(12), 2247–2249 (2012).
[Crossref] [PubMed]

K. Kamada, Y. Ito, and T. Kobayashi, “Human MCG measurements with a high-sensitivity potassium atomic magnetometer,” Physiol. Meas. 33(6), 1063–1071 (2012).
[Crossref] [PubMed]

R. Wyllie, M. Kauer, G. S. Smetana, R. T. Wakai, and T. G. Walker, “Magnetocardiography with a modular spin-exchange relaxation-free atomic magnetometer array,” Phys. Med. Biol. 57(9), 2619–2632 (2012).
[Crossref] [PubMed]

2010 (3)

S. Knappe, T. H. Sander, O. Kosch, F. Wiekhorst, J. Kitching, and L. Trahms, “Cross-validation of microfabricated atomic magnetometers with superconducting quantum interference devices for biomagnetic applications,” Appl. Phys. Lett. 97(13), 133703 (2010).
[Crossref]

C. Johnson, P. D. D. Schwindt, and M. Weisend, “Magnetoencephalography with a two-color pump-probe, fiber-coupled atomic magnetometer,” Appl. Phys. Lett. 97(24), 243703 (2010).
[Crossref]

H. B. Dang, A. C. Maloof, and M. V. Romalis, “Ultrahigh sensitivity magnetic field and magnetization measurements with an atomic magnetometer,” Appl. Phys. Lett. 97(15), 151110 (2010).
[Crossref]

2009 (1)

G. Bison, N. Castagna, A. Hofer, P. Knowles, J. L. Schenker, M. Kasprzak, H. Saudan, and A. Weis, “A room temperature 19-channel magnetic field mapping device for cardiac signals,” Appl. Phys. Lett. 95(17), 173701 (2009).
[Crossref]

2008 (1)

M. P. Ledbetter, I. M. Savukov, V. M. Acosta, D. Budker, and M. V. Romalis, “Spin-exchange-relaxation-free magnetometry with Cs vapor,” Phys. Rev. A 77(3), 033408 (2008).
[Crossref]

2007 (5)

M. A. Rosenberry, J. P. Reyes, D. Tupa, and T. J. Gay, “Radiation trapping in rubidium optical pumping at low buffer-gas pressures,” Phys. Rev. A 75(2), 023401 (2007).
[Crossref]

J. Belfi, G. Bevilacqua, V. Biancalana, S. Cartaleva, Y. Dancheva, and L. Moi, “Cesium coherent population trapping magnetometer for cardiosignal detection in an unshielded environment,” J. Opt. Soc. Am. B 24(9), 2357–2362 (2007).
[Crossref]

K. Kim, W.-K. Lee, I.-S. Kim, and H. S. Moon, “Atomic vector gradiometer system using cesium vapor cells for magnetocardiography: perspective on practical application,” IEEE Trans. Instrum. Meas. 56(2), 458–462 (2007).
[Crossref]

F. Gong, Y. Y. Jau, and W. Happer, “Magnetic resonance reversals in optically pumped alkali-metal vapor,” Phys. Rev. A 75(5), 053415 (2007).
[Crossref]

T. W. Kornack, S. J. Smullin, S. K. Lee, and M. V. Romalis, “A low-noise ferrite magnetic shield,” Appl. Phys. Lett. 90(22), 223501 (2007).
[Crossref]

2006 (2)

K. Sternickel and A. I. Braginski, “Biomagnetism using SQUIDs: status and perspectives,” Supercond. Sci. Technol. 19(3), S160–S171 (2006).
[Crossref]

H. Xia, A. Ben-Amar Baranga, D. Hoffman, and M. V. Romalis, “Magnetoencephalography with an atomic magnetometer,” Appl. Phys. Lett. 89(21), 211104 (2006).
[Crossref]

2005 (1)

I. M. Savukov and M. V. Romalis, “Effects of spin-exchange collisions in a high-density alkali-metal vapor in low magnetic fields,” Phys. Rev. A 71(2), 023405 (2005).
[Crossref]

2004 (2)

S. Taulu, M. Kajola, and J. Simola, “Suppression of Interference and Artifacts by the Signal Space Separation Method,” Brain Topogr. 16(4), 269–275 (2004).
[Crossref] [PubMed]

H. Koch, “Recent advances in magnetocardiography,” J. Electrocardiol. 37(Suppl), 117–122 (2004).
[Crossref] [PubMed]

2003 (3)

G. Bison, R. Wynands, and A. Weis, “A laser-pumped magnetometer for the mapping of human cardiomagnetic fields,” Appl. Phys. B 76(3), 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(8), 904–909 (2003).
[Crossref] [PubMed]

I. K. Kominis, T. W. Kornack, J. C. Allred, and M. V. Romalis, “A subfemtotesla multichannel atomic magnetometer,” Nature 422(6932), 596–599 (2003).
[Crossref] [PubMed]

2002 (2)

J. C. Allred, R. N. Lyman, T. W. Kornack, and M. V. Romalis, “High-Sensitivity Atomic Magnetometer Unaffected by Spin-Exchange Relaxation,” Phys. Rev. Lett. 89(13), 130801 (2002).
[Crossref] [PubMed]

B. Chann, E. Babcock, L. W. Anderson, and T. G. Walker, “Skew light propagation in optically thick optical pumping cells,” Phys. Rev. A 66(3), 033406 (2002).
[Crossref]

1998 (1)

S. Appelt, A. B.-A. Baranga, C. J. Erickson, M. V. Romalis, A. R. Young, and W. Happer, “Theory of spin-exchange optical pumping of 3He and 129Xe,” Phys. Rev. A 58(2), 1412–1439 (1998).
[Crossref]

1997 (1)

M. A. Uusitalo and R. J. Ilmoniemi, “Signal-space projection method for separating MEG or EEG into components,” Med. Biol. Eng. Comput. 35(2), 135–140 (1997).
[Crossref] [PubMed]

1993 (1)

M. Hämäläinen, R. Hari, R. J. Ilmoniemi, J. Knuutila, and O. V. Lounasmaa, “Magnetoencephalography—theory, instrumentation, and applications to noninvasive studies of the working human brain,” Rev. Mod. Phys. 65(2), 413–497 (1993).
[Crossref]

1990 (1)

M. Rosatzin, D. Suter, and J. Mlynek, “Light-shift-induced spin echoes in a J=1/2 atomic ground state,” Phys. Rev. A 42(3), 1839–1841 (1990).
[Crossref] [PubMed]

1983 (1)

I. O. Fomin, S. E. Sinel’nikova, A. N. Kozlov, V. N. Uranov, and V. A. Gorshkov, “Registration of the heart’s magnetic field,” Kardiologiia 23(10), 66–68 (1983).
[PubMed]

1981 (1)

M. N. Livanov, A. N. Koslov, S. E. Sinelnikova, J. A. Kholodov, V. P. Markin, A. M. Gorbach, and A. V. Korinewsky, “Record of the human magnetocardiogram by the quantum gradiometer with optical pumping,” Adv. Cardiol. 28, 78–80 (1981).
[Crossref] [PubMed]

1972 (1)

C. Cohen-Tannoudji and J. Dupont-Roc, “Experimental study of Zeeman light shifts in weak magnetic fields,” Phys. Rev. A 5(2), 968–984 (1972).
[Crossref]

Acosta, V. M.

M. P. Ledbetter, I. M. Savukov, V. M. Acosta, D. Budker, and M. V. Romalis, “Spin-exchange-relaxation-free magnetometry with Cs vapor,” Phys. Rev. A 77(3), 033408 (2008).
[Crossref]

Alem, O.

O. Alem, T. H. Sander, R. Mhaskar, J. LeBlanc, H. Eswaran, U. Steinhoff, Y. Okada, J. Kitching, L. Trahms, and S. Knappe, “Fetal magnetocardiography measurements with an array of microfabricated optically pumped magnetometers,” Phys. Med. Biol. 60(12), 4797–4811 (2015).
[Crossref] [PubMed]

O. Alem, A. M. Benison, D. S. Barth, J. Kitching, and S. Knappe, “Magnetoencephalography of epilepsy with a microfabricated atomic magnetrode,” J. Neurosci. 34(43), 14324–14327 (2014).
[Crossref] [PubMed]

Allred, J. C.

I. K. Kominis, T. W. Kornack, J. C. Allred, and M. V. Romalis, “A subfemtotesla multichannel atomic magnetometer,” Nature 422(6932), 596–599 (2003).
[Crossref] [PubMed]

J. C. Allred, R. N. Lyman, T. W. Kornack, and M. V. Romalis, “High-Sensitivity Atomic Magnetometer Unaffected by Spin-Exchange Relaxation,” Phys. Rev. Lett. 89(13), 130801 (2002).
[Crossref] [PubMed]

Anderson, L. W.

B. Chann, E. Babcock, L. W. Anderson, and T. G. Walker, “Skew light propagation in optically thick optical pumping cells,” Phys. Rev. A 66(3), 033406 (2002).
[Crossref]

Appelt, S.

S. Appelt, A. B.-A. Baranga, C. J. Erickson, M. V. Romalis, A. R. Young, and W. Happer, “Theory of spin-exchange optical pumping of 3He and 129Xe,” Phys. Rev. A 58(2), 1412–1439 (1998).
[Crossref]

Babcock, E.

B. Chann, E. Babcock, L. W. Anderson, and T. G. Walker, “Skew light propagation in optically thick optical pumping cells,” Phys. Rev. A 66(3), 033406 (2002).
[Crossref]

Ban, K.

N. Mizutani, K. Okano, K. Ban, S. Ichihara, A. Terao, and T. Kobayashi, “A plateau in the sensitivity of a compact optically pumped atomic magnetometer,” AIP Adv. 4(5), 057132 (2014).
[Crossref]

Baranga, A. B.-A.

S. Appelt, A. B.-A. Baranga, C. J. Erickson, M. V. Romalis, A. R. Young, and W. Happer, “Theory of spin-exchange optical pumping of 3He and 129Xe,” Phys. Rev. A 58(2), 1412–1439 (1998).
[Crossref]

Barth, D. S.

O. Alem, A. M. Benison, D. S. Barth, J. Kitching, and S. Knappe, “Magnetoencephalography of epilepsy with a microfabricated atomic magnetrode,” J. Neurosci. 34(43), 14324–14327 (2014).
[Crossref] [PubMed]

Begus, S.

K. Kim, S. Begus, H. Xia, S. K. Lee, V. Jazbinsek, Z. Trontelj, and M. V. Romalis, “Multi-channel atomic magnetometer for magnetoencephalography: a configuration study,” Neuroimage 89, 143–151 (2014).
[Crossref] [PubMed]

Belfi, J.

Ben-Amar Baranga, A.

H. Xia, A. Ben-Amar Baranga, D. Hoffman, and M. V. Romalis, “Magnetoencephalography with an atomic magnetometer,” Appl. Phys. Lett. 89(21), 211104 (2006).
[Crossref]

Benison, A. M.

O. Alem, A. M. Benison, D. S. Barth, J. Kitching, and S. Knappe, “Magnetoencephalography of epilepsy with a microfabricated atomic magnetrode,” J. Neurosci. 34(43), 14324–14327 (2014).
[Crossref] [PubMed]

Bevilacqua, G.

Biancalana, V.

Bison, G.

G. Lembke, S. N. Erné, H. Nowak, B. Menhorn, A. Pasquarelli, and G. Bison, “Optical multichannel room temperature magnetic field imaging system for clinical application,” Biomed. Opt. Express 5(3), 876–881 (2014).
[Crossref] [PubMed]

G. Bison, N. Castagna, A. Hofer, P. Knowles, J. L. Schenker, M. Kasprzak, H. Saudan, and A. Weis, “A room temperature 19-channel magnetic field mapping device for cardiac signals,” Appl. Phys. Lett. 95(17), 173701 (2009).
[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(8), 904–909 (2003).
[Crossref] [PubMed]

G. Bison, R. Wynands, and A. Weis, “A laser-pumped magnetometer for the mapping of human cardiomagnetic fields,” Appl. Phys. B 76(3), 325–328 (2003).
[Crossref]

Braginski, A. I.

K. Sternickel and A. I. Braginski, “Biomagnetism using SQUIDs: status and perspectives,” Supercond. Sci. Technol. 19(3), S160–S171 (2006).
[Crossref]

Budker, D.

M. P. Ledbetter, I. M. Savukov, V. M. Acosta, D. Budker, and M. V. Romalis, “Spin-exchange-relaxation-free magnetometry with Cs vapor,” Phys. Rev. A 77(3), 033408 (2008).
[Crossref]

Cartaleva, S.

Castagna, N.

G. Bison, N. Castagna, A. Hofer, P. Knowles, J. L. Schenker, M. Kasprzak, H. Saudan, and A. Weis, “A room temperature 19-channel magnetic field mapping device for cardiac signals,” Appl. Phys. Lett. 95(17), 173701 (2009).
[Crossref]

Chann, B.

B. Chann, E. Babcock, L. W. Anderson, and T. G. Walker, “Skew light propagation in optically thick optical pumping cells,” Phys. Rev. A 66(3), 033406 (2002).
[Crossref]

Cohen-Tannoudji, C.

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O. Alem, T. H. Sander, R. Mhaskar, J. LeBlanc, H. Eswaran, U. Steinhoff, Y. Okada, J. Kitching, L. Trahms, and S. Knappe, “Fetal magnetocardiography measurements with an array of microfabricated optically pumped magnetometers,” Phys. Med. Biol. 60(12), 4797–4811 (2015).
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I. O. Fomin, S. E. Sinel’nikova, A. N. Kozlov, V. N. Uranov, and V. A. Gorshkov, “Registration of the heart’s magnetic field,” Kardiologiia 23(10), 66–68 (1983).
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M. A. Rosenberry, J. P. Reyes, D. Tupa, and T. J. Gay, “Radiation trapping in rubidium optical pumping at low buffer-gas pressures,” Phys. Rev. A 75(2), 023401 (2007).
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M. N. Livanov, A. N. Koslov, S. E. Sinelnikova, J. A. Kholodov, V. P. Markin, A. M. Gorbach, and A. V. Korinewsky, “Record of the human magnetocardiogram by the quantum gradiometer with optical pumping,” Adv. Cardiol. 28, 78–80 (1981).
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I. O. Fomin, S. E. Sinel’nikova, A. N. Kozlov, V. N. Uranov, and V. A. Gorshkov, “Registration of the heart’s magnetic field,” Kardiologiia 23(10), 66–68 (1983).
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M. Hämäläinen, R. Hari, R. J. Ilmoniemi, J. Knuutila, and O. V. Lounasmaa, “Magnetoencephalography—theory, instrumentation, and applications to noninvasive studies of the working human brain,” Rev. Mod. Phys. 65(2), 413–497 (1993).
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N. Mizutani, K. Okano, K. Ban, S. Ichihara, A. Terao, and T. Kobayashi, “A plateau in the sensitivity of a compact optically pumped atomic magnetometer,” AIP Adv. 4(5), 057132 (2014).
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C. Johnson, P. D. D. Schwindt, and M. Weisend, “Magnetoencephalography with a two-color pump-probe, fiber-coupled atomic magnetometer,” Appl. Phys. Lett. 97(24), 243703 (2010).
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C. N. Johnson, P. D. D. Schwindt, and M. Weisend, “Multi-sensor magnetoencephalography with atomic magnetometers,” Phys. Med. Biol. 58(17), 6065–6077 (2013).
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S. Taulu, M. Kajola, and J. Simola, “Suppression of Interference and Artifacts by the Signal Space Separation Method,” Brain Topogr. 16(4), 269–275 (2004).
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K. Kamada, Y. Ito, and T. Kobayashi, “Human MCG measurements with a high-sensitivity potassium atomic magnetometer,” Physiol. Meas. 33(6), 1063–1071 (2012).
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G. Bison, N. Castagna, A. Hofer, P. Knowles, J. L. Schenker, M. Kasprzak, H. Saudan, and A. Weis, “A room temperature 19-channel magnetic field mapping device for cardiac signals,” Appl. Phys. Lett. 95(17), 173701 (2009).
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K. Kim, W.-K. Lee, I.-S. Kim, and H. S. Moon, “Atomic vector gradiometer system using cesium vapor cells for magnetocardiography: perspective on practical application,” IEEE Trans. Instrum. Meas. 56(2), 458–462 (2007).
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Kim, K.

K. Kim, S. Begus, H. Xia, S. K. Lee, V. Jazbinsek, Z. Trontelj, and M. V. Romalis, “Multi-channel atomic magnetometer for magnetoencephalography: a configuration study,” Neuroimage 89, 143–151 (2014).
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K. Kim, W.-K. Lee, I.-S. Kim, and H. S. Moon, “Atomic vector gradiometer system using cesium vapor cells for magnetocardiography: perspective on practical application,” IEEE Trans. Instrum. Meas. 56(2), 458–462 (2007).
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Kitching, J.

O. Alem, T. H. Sander, R. Mhaskar, J. LeBlanc, H. Eswaran, U. Steinhoff, Y. Okada, J. Kitching, L. Trahms, and S. Knappe, “Fetal magnetocardiography measurements with an array of microfabricated optically pumped magnetometers,” Phys. Med. Biol. 60(12), 4797–4811 (2015).
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T. H. Sander, J. Preusser, R. Mhaskar, J. Kitching, L. Trahms, and S. Knappe, “Magnetoencephalography with a chip-scale atomic magnetometer,” Biomed. Opt. Express 3(5), 981–990 (2012).
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S. Knappe, T. H. Sander, O. Kosch, F. Wiekhorst, J. Kitching, and L. Trahms, “Cross-validation of microfabricated atomic magnetometers with superconducting quantum interference devices for biomagnetic applications,” Appl. Phys. Lett. 97(13), 133703 (2010).
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Knappe, S.

O. Alem, T. H. Sander, R. Mhaskar, J. LeBlanc, H. Eswaran, U. Steinhoff, Y. Okada, J. Kitching, L. Trahms, and S. Knappe, “Fetal magnetocardiography measurements with an array of microfabricated optically pumped magnetometers,” Phys. Med. Biol. 60(12), 4797–4811 (2015).
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O. Alem, A. M. Benison, D. S. Barth, J. Kitching, and S. Knappe, “Magnetoencephalography of epilepsy with a microfabricated atomic magnetrode,” J. Neurosci. 34(43), 14324–14327 (2014).
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T. H. Sander, J. Preusser, R. Mhaskar, J. Kitching, L. Trahms, and S. Knappe, “Magnetoencephalography with a chip-scale atomic magnetometer,” Biomed. Opt. Express 3(5), 981–990 (2012).
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S. Knappe, T. H. Sander, O. Kosch, F. Wiekhorst, J. Kitching, and L. Trahms, “Cross-validation of microfabricated atomic magnetometers with superconducting quantum interference devices for biomagnetic applications,” Appl. Phys. Lett. 97(13), 133703 (2010).
[Crossref]

Knowles, P.

G. Bison, N. Castagna, A. Hofer, P. Knowles, J. L. Schenker, M. Kasprzak, H. Saudan, and A. Weis, “A room temperature 19-channel magnetic field mapping device for cardiac signals,” Appl. Phys. Lett. 95(17), 173701 (2009).
[Crossref]

Knuutila, J.

M. Hämäläinen, R. Hari, R. J. Ilmoniemi, J. Knuutila, and O. V. Lounasmaa, “Magnetoencephalography—theory, instrumentation, and applications to noninvasive studies of the working human brain,” Rev. Mod. Phys. 65(2), 413–497 (1993).
[Crossref]

Kobayashi, T.

N. Mizutani, K. Okano, K. Ban, S. Ichihara, A. Terao, and T. Kobayashi, “A plateau in the sensitivity of a compact optically pumped atomic magnetometer,” AIP Adv. 4(5), 057132 (2014).
[Crossref]

K. Kamada, Y. Ito, and T. Kobayashi, “Human MCG measurements with a high-sensitivity potassium atomic magnetometer,” Physiol. Meas. 33(6), 1063–1071 (2012).
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H. Koch, “Recent advances in magnetocardiography,” J. Electrocardiol. 37(Suppl), 117–122 (2004).
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I. K. Kominis, T. W. Kornack, J. C. Allred, and M. V. Romalis, “A subfemtotesla multichannel atomic magnetometer,” Nature 422(6932), 596–599 (2003).
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Korinewsky, A. V.

M. N. Livanov, A. N. Koslov, S. E. Sinelnikova, J. A. Kholodov, V. P. Markin, A. M. Gorbach, and A. V. Korinewsky, “Record of the human magnetocardiogram by the quantum gradiometer with optical pumping,” Adv. Cardiol. 28, 78–80 (1981).
[Crossref] [PubMed]

Kornack, T. W.

T. W. Kornack, S. J. Smullin, S. K. Lee, and M. V. Romalis, “A low-noise ferrite magnetic shield,” Appl. Phys. Lett. 90(22), 223501 (2007).
[Crossref]

I. K. Kominis, T. W. Kornack, J. C. Allred, and M. V. Romalis, “A subfemtotesla multichannel atomic magnetometer,” Nature 422(6932), 596–599 (2003).
[Crossref] [PubMed]

J. C. Allred, R. N. Lyman, T. W. Kornack, and M. V. Romalis, “High-Sensitivity Atomic Magnetometer Unaffected by Spin-Exchange Relaxation,” Phys. Rev. Lett. 89(13), 130801 (2002).
[Crossref] [PubMed]

Kosch, O.

S. Knappe, T. H. Sander, O. Kosch, F. Wiekhorst, J. Kitching, and L. Trahms, “Cross-validation of microfabricated atomic magnetometers with superconducting quantum interference devices for biomagnetic applications,” Appl. Phys. Lett. 97(13), 133703 (2010).
[Crossref]

Koslov, A. N.

M. N. Livanov, A. N. Koslov, S. E. Sinelnikova, J. A. Kholodov, V. P. Markin, A. M. Gorbach, and A. V. Korinewsky, “Record of the human magnetocardiogram by the quantum gradiometer with optical pumping,” Adv. Cardiol. 28, 78–80 (1981).
[Crossref] [PubMed]

Kozlov, A. N.

I. O. Fomin, S. E. Sinel’nikova, A. N. Kozlov, V. N. Uranov, and V. A. Gorshkov, “Registration of the heart’s magnetic field,” Kardiologiia 23(10), 66–68 (1983).
[PubMed]

LeBlanc, J.

O. Alem, T. H. Sander, R. Mhaskar, J. LeBlanc, H. Eswaran, U. Steinhoff, Y. Okada, J. Kitching, L. Trahms, and S. Knappe, “Fetal magnetocardiography measurements with an array of microfabricated optically pumped magnetometers,” Phys. Med. Biol. 60(12), 4797–4811 (2015).
[Crossref] [PubMed]

Ledbetter, M. P.

M. P. Ledbetter, I. M. Savukov, V. M. Acosta, D. Budker, and M. V. Romalis, “Spin-exchange-relaxation-free magnetometry with Cs vapor,” Phys. Rev. A 77(3), 033408 (2008).
[Crossref]

Lee, S. K.

K. Kim, S. Begus, H. Xia, S. K. Lee, V. Jazbinsek, Z. Trontelj, and M. V. Romalis, “Multi-channel atomic magnetometer for magnetoencephalography: a configuration study,” Neuroimage 89, 143–151 (2014).
[Crossref] [PubMed]

T. W. Kornack, S. J. Smullin, S. K. Lee, and M. V. Romalis, “A low-noise ferrite magnetic shield,” Appl. Phys. Lett. 90(22), 223501 (2007).
[Crossref]

Lee, W.-K.

K. Kim, W.-K. Lee, I.-S. Kim, and H. S. Moon, “Atomic vector gradiometer system using cesium vapor cells for magnetocardiography: perspective on practical application,” IEEE Trans. Instrum. Meas. 56(2), 458–462 (2007).
[Crossref]

Lembke, G.

Livanov, M. N.

M. N. Livanov, A. N. Koslov, S. E. Sinelnikova, J. A. Kholodov, V. P. Markin, A. M. Gorbach, and A. V. Korinewsky, “Record of the human magnetocardiogram by the quantum gradiometer with optical pumping,” Adv. Cardiol. 28, 78–80 (1981).
[Crossref] [PubMed]

Lounasmaa, O. V.

M. Hämäläinen, R. Hari, R. J. Ilmoniemi, J. Knuutila, and O. V. Lounasmaa, “Magnetoencephalography—theory, instrumentation, and applications to noninvasive studies of the working human brain,” Rev. Mod. Phys. 65(2), 413–497 (1993).
[Crossref]

Lyman, R. N.

J. C. Allred, R. N. Lyman, T. W. Kornack, and M. V. Romalis, “High-Sensitivity Atomic Magnetometer Unaffected by Spin-Exchange Relaxation,” Phys. Rev. Lett. 89(13), 130801 (2002).
[Crossref] [PubMed]

Maloof, A. C.

H. B. Dang, A. C. Maloof, and M. V. Romalis, “Ultrahigh sensitivity magnetic field and magnetization measurements with an atomic magnetometer,” Appl. Phys. Lett. 97(15), 151110 (2010).
[Crossref]

Markin, V. P.

M. N. Livanov, A. N. Koslov, S. E. Sinelnikova, J. A. Kholodov, V. P. Markin, A. M. Gorbach, and A. V. Korinewsky, “Record of the human magnetocardiogram by the quantum gradiometer with optical pumping,” Adv. Cardiol. 28, 78–80 (1981).
[Crossref] [PubMed]

Menhorn, B.

Mhaskar, R.

O. Alem, T. H. Sander, R. Mhaskar, J. LeBlanc, H. Eswaran, U. Steinhoff, Y. Okada, J. Kitching, L. Trahms, and S. Knappe, “Fetal magnetocardiography measurements with an array of microfabricated optically pumped magnetometers,” Phys. Med. Biol. 60(12), 4797–4811 (2015).
[Crossref] [PubMed]

T. H. Sander, J. Preusser, R. Mhaskar, J. Kitching, L. Trahms, and S. Knappe, “Magnetoencephalography with a chip-scale atomic magnetometer,” Biomed. Opt. Express 3(5), 981–990 (2012).
[Crossref] [PubMed]

Mizutani, N.

N. Mizutani, K. Okano, K. Ban, S. Ichihara, A. Terao, and T. Kobayashi, “A plateau in the sensitivity of a compact optically pumped atomic magnetometer,” AIP Adv. 4(5), 057132 (2014).
[Crossref]

Mlynek, J.

M. Rosatzin, D. Suter, and J. Mlynek, “Light-shift-induced spin echoes in a J=1/2 atomic ground state,” Phys. Rev. A 42(3), 1839–1841 (1990).
[Crossref] [PubMed]

Moi, L.

Moon, H. S.

K. Kim, W.-K. Lee, I.-S. Kim, and H. S. Moon, “Atomic vector gradiometer system using cesium vapor cells for magnetocardiography: perspective on practical application,” IEEE Trans. Instrum. Meas. 56(2), 458–462 (2007).
[Crossref]

Nowak, H.

Okada, Y.

O. Alem, T. H. Sander, R. Mhaskar, J. LeBlanc, H. Eswaran, U. Steinhoff, Y. Okada, J. Kitching, L. Trahms, and S. Knappe, “Fetal magnetocardiography measurements with an array of microfabricated optically pumped magnetometers,” Phys. Med. Biol. 60(12), 4797–4811 (2015).
[Crossref] [PubMed]

Okano, K.

N. Mizutani, K. Okano, K. Ban, S. Ichihara, A. Terao, and T. Kobayashi, “A plateau in the sensitivity of a compact optically pumped atomic magnetometer,” AIP Adv. 4(5), 057132 (2014).
[Crossref]

Pasquarelli, A.

Preusser, J.

Reyes, J. P.

M. A. Rosenberry, J. P. Reyes, D. Tupa, and T. J. Gay, “Radiation trapping in rubidium optical pumping at low buffer-gas pressures,” Phys. Rev. A 75(2), 023401 (2007).
[Crossref]

Romalis, M. V.

K. Kim, S. Begus, H. Xia, S. K. Lee, V. Jazbinsek, Z. Trontelj, and M. V. Romalis, “Multi-channel atomic magnetometer for magnetoencephalography: a configuration study,” Neuroimage 89, 143–151 (2014).
[Crossref] [PubMed]

H. B. Dang, A. C. Maloof, and M. V. Romalis, “Ultrahigh sensitivity magnetic field and magnetization measurements with an atomic magnetometer,” Appl. Phys. Lett. 97(15), 151110 (2010).
[Crossref]

M. P. Ledbetter, I. M. Savukov, V. M. Acosta, D. Budker, and M. V. Romalis, “Spin-exchange-relaxation-free magnetometry with Cs vapor,” Phys. Rev. A 77(3), 033408 (2008).
[Crossref]

T. W. Kornack, S. J. Smullin, S. K. Lee, and M. V. Romalis, “A low-noise ferrite magnetic shield,” Appl. Phys. Lett. 90(22), 223501 (2007).
[Crossref]

H. Xia, A. Ben-Amar Baranga, D. Hoffman, and M. V. Romalis, “Magnetoencephalography with an atomic magnetometer,” Appl. Phys. Lett. 89(21), 211104 (2006).
[Crossref]

I. M. Savukov and M. V. Romalis, “Effects of spin-exchange collisions in a high-density alkali-metal vapor in low magnetic fields,” Phys. Rev. A 71(2), 023405 (2005).
[Crossref]

I. K. Kominis, T. W. Kornack, J. C. Allred, and M. V. Romalis, “A subfemtotesla multichannel atomic magnetometer,” Nature 422(6932), 596–599 (2003).
[Crossref] [PubMed]

J. C. Allred, R. N. Lyman, T. W. Kornack, and M. V. Romalis, “High-Sensitivity Atomic Magnetometer Unaffected by Spin-Exchange Relaxation,” Phys. Rev. Lett. 89(13), 130801 (2002).
[Crossref] [PubMed]

S. Appelt, A. B.-A. Baranga, C. J. Erickson, M. V. Romalis, A. R. Young, and W. Happer, “Theory of spin-exchange optical pumping of 3He and 129Xe,” Phys. Rev. A 58(2), 1412–1439 (1998).
[Crossref]

Rosatzin, M.

M. Rosatzin, D. Suter, and J. Mlynek, “Light-shift-induced spin echoes in a J=1/2 atomic ground state,” Phys. Rev. A 42(3), 1839–1841 (1990).
[Crossref] [PubMed]

Rosenberry, M. A.

M. A. Rosenberry, J. P. Reyes, D. Tupa, and T. J. Gay, “Radiation trapping in rubidium optical pumping at low buffer-gas pressures,” Phys. Rev. A 75(2), 023401 (2007).
[Crossref]

Sander, T. H.

O. Alem, T. H. Sander, R. Mhaskar, J. LeBlanc, H. Eswaran, U. Steinhoff, Y. Okada, J. Kitching, L. Trahms, and S. Knappe, “Fetal magnetocardiography measurements with an array of microfabricated optically pumped magnetometers,” Phys. Med. Biol. 60(12), 4797–4811 (2015).
[Crossref] [PubMed]

T. H. Sander, J. Preusser, R. Mhaskar, J. Kitching, L. Trahms, and S. Knappe, “Magnetoencephalography with a chip-scale atomic magnetometer,” Biomed. Opt. Express 3(5), 981–990 (2012).
[Crossref] [PubMed]

S. Knappe, T. H. Sander, O. Kosch, F. Wiekhorst, J. Kitching, and L. Trahms, “Cross-validation of microfabricated atomic magnetometers with superconducting quantum interference devices for biomagnetic applications,” Appl. Phys. Lett. 97(13), 133703 (2010).
[Crossref]

Saudan, H.

G. Bison, N. Castagna, A. Hofer, P. Knowles, J. L. Schenker, M. Kasprzak, H. Saudan, and A. Weis, “A room temperature 19-channel magnetic field mapping device for cardiac signals,” Appl. Phys. Lett. 95(17), 173701 (2009).
[Crossref]

Savukov, I. M.

M. P. Ledbetter, I. M. Savukov, V. M. Acosta, D. Budker, and M. V. Romalis, “Spin-exchange-relaxation-free magnetometry with Cs vapor,” Phys. Rev. A 77(3), 033408 (2008).
[Crossref]

I. M. Savukov and M. V. Romalis, “Effects of spin-exchange collisions in a high-density alkali-metal vapor in low magnetic fields,” Phys. Rev. A 71(2), 023405 (2005).
[Crossref]

Schenker, J. L.

G. Bison, N. Castagna, A. Hofer, P. Knowles, J. L. Schenker, M. Kasprzak, H. Saudan, and A. Weis, “A room temperature 19-channel magnetic field mapping device for cardiac signals,” Appl. Phys. Lett. 95(17), 173701 (2009).
[Crossref]

Schwindt, P. D. D.

C. N. Johnson, P. D. D. Schwindt, and M. Weisend, “Multi-sensor magnetoencephalography with atomic magnetometers,” Phys. Med. Biol. 58(17), 6065–6077 (2013).
[Crossref] [PubMed]

C. Johnson, P. D. D. Schwindt, and M. Weisend, “Magnetoencephalography with a two-color pump-probe, fiber-coupled atomic magnetometer,” Appl. Phys. Lett. 97(24), 243703 (2010).
[Crossref]

Shah, V. K.

V. K. Shah and R. T. Wakai, “A compact, high performance atomic magnetometer for biomedical applications,” Phys. Med. Biol. 58(22), 8153–8161 (2013).
[Crossref] [PubMed]

Simola, J.

S. Taulu, M. Kajola, and J. Simola, “Suppression of Interference and Artifacts by the Signal Space Separation Method,” Brain Topogr. 16(4), 269–275 (2004).
[Crossref] [PubMed]

Sinel’nikova, S. E.

I. O. Fomin, S. E. Sinel’nikova, A. N. Kozlov, V. N. Uranov, and V. A. Gorshkov, “Registration of the heart’s magnetic field,” Kardiologiia 23(10), 66–68 (1983).
[PubMed]

Sinelnikova, S. E.

M. N. Livanov, A. N. Koslov, S. E. Sinelnikova, J. A. Kholodov, V. P. Markin, A. M. Gorbach, and A. V. Korinewsky, “Record of the human magnetocardiogram by the quantum gradiometer with optical pumping,” Adv. Cardiol. 28, 78–80 (1981).
[Crossref] [PubMed]

Smetana, G. S.

R. Wyllie, M. Kauer, G. S. Smetana, R. T. Wakai, and T. G. Walker, “Magnetocardiography with a modular spin-exchange relaxation-free atomic magnetometer array,” Phys. Med. Biol. 57(9), 2619–2632 (2012).
[Crossref] [PubMed]

Smullin, S. J.

T. W. Kornack, S. J. Smullin, S. K. Lee, and M. V. Romalis, “A low-noise ferrite magnetic shield,” Appl. Phys. Lett. 90(22), 223501 (2007).
[Crossref]

Steinhoff, U.

O. Alem, T. H. Sander, R. Mhaskar, J. LeBlanc, H. Eswaran, U. Steinhoff, Y. Okada, J. Kitching, L. Trahms, and S. Knappe, “Fetal magnetocardiography measurements with an array of microfabricated optically pumped magnetometers,” Phys. Med. Biol. 60(12), 4797–4811 (2015).
[Crossref] [PubMed]

Sternickel, K.

K. Sternickel and A. I. Braginski, “Biomagnetism using SQUIDs: status and perspectives,” Supercond. Sci. Technol. 19(3), S160–S171 (2006).
[Crossref]

Suter, D.

M. Rosatzin, D. Suter, and J. Mlynek, “Light-shift-induced spin echoes in a J=1/2 atomic ground state,” Phys. Rev. A 42(3), 1839–1841 (1990).
[Crossref] [PubMed]

Taulu, S.

S. Taulu, M. Kajola, and J. Simola, “Suppression of Interference and Artifacts by the Signal Space Separation Method,” Brain Topogr. 16(4), 269–275 (2004).
[Crossref] [PubMed]

Terao, A.

N. Mizutani, K. Okano, K. Ban, S. Ichihara, A. Terao, and T. Kobayashi, “A plateau in the sensitivity of a compact optically pumped atomic magnetometer,” AIP Adv. 4(5), 057132 (2014).
[Crossref]

Trahms, L.

O. Alem, T. H. Sander, R. Mhaskar, J. LeBlanc, H. Eswaran, U. Steinhoff, Y. Okada, J. Kitching, L. Trahms, and S. Knappe, “Fetal magnetocardiography measurements with an array of microfabricated optically pumped magnetometers,” Phys. Med. Biol. 60(12), 4797–4811 (2015).
[Crossref] [PubMed]

T. H. Sander, J. Preusser, R. Mhaskar, J. Kitching, L. Trahms, and S. Knappe, “Magnetoencephalography with a chip-scale atomic magnetometer,” Biomed. Opt. Express 3(5), 981–990 (2012).
[Crossref] [PubMed]

S. Knappe, T. H. Sander, O. Kosch, F. Wiekhorst, J. Kitching, and L. Trahms, “Cross-validation of microfabricated atomic magnetometers with superconducting quantum interference devices for biomagnetic applications,” Appl. Phys. Lett. 97(13), 133703 (2010).
[Crossref]

Trontelj, Z.

K. Kim, S. Begus, H. Xia, S. K. Lee, V. Jazbinsek, Z. Trontelj, and M. V. Romalis, “Multi-channel atomic magnetometer for magnetoencephalography: a configuration study,” Neuroimage 89, 143–151 (2014).
[Crossref] [PubMed]

Tupa, D.

M. A. Rosenberry, J. P. Reyes, D. Tupa, and T. J. Gay, “Radiation trapping in rubidium optical pumping at low buffer-gas pressures,” Phys. Rev. A 75(2), 023401 (2007).
[Crossref]

Uranov, V. N.

I. O. Fomin, S. E. Sinel’nikova, A. N. Kozlov, V. N. Uranov, and V. A. Gorshkov, “Registration of the heart’s magnetic field,” Kardiologiia 23(10), 66–68 (1983).
[PubMed]

Uusitalo, M. A.

M. A. Uusitalo and R. J. Ilmoniemi, “Signal-space projection method for separating MEG or EEG into components,” Med. Biol. Eng. Comput. 35(2), 135–140 (1997).
[Crossref] [PubMed]

Wakai, R. T.

V. K. Shah and R. T. Wakai, “A compact, high performance atomic magnetometer for biomedical applications,” Phys. Med. Biol. 58(22), 8153–8161 (2013).
[Crossref] [PubMed]

R. Wyllie, M. Kauer, G. S. Smetana, R. T. Wakai, and T. G. Walker, “Magnetocardiography with a modular spin-exchange relaxation-free atomic magnetometer array,” Phys. Med. Biol. 57(9), 2619–2632 (2012).
[Crossref] [PubMed]

R. Wyllie, M. Kauer, R. T. Wakai, and T. G. Walker, “Optical magnetometer array for fetal magnetocardiography,” Opt. Lett. 37(12), 2247–2249 (2012).
[Crossref] [PubMed]

Walker, T. G.

R. Wyllie, M. Kauer, R. T. Wakai, and T. G. Walker, “Optical magnetometer array for fetal magnetocardiography,” Opt. Lett. 37(12), 2247–2249 (2012).
[Crossref] [PubMed]

R. Wyllie, M. Kauer, G. S. Smetana, R. T. Wakai, and T. G. Walker, “Magnetocardiography with a modular spin-exchange relaxation-free atomic magnetometer array,” Phys. Med. Biol. 57(9), 2619–2632 (2012).
[Crossref] [PubMed]

B. Chann, E. Babcock, L. W. Anderson, and T. G. Walker, “Skew light propagation in optically thick optical pumping cells,” Phys. Rev. A 66(3), 033406 (2002).
[Crossref]

Weis, A.

G. Bison, N. Castagna, A. Hofer, P. Knowles, J. L. Schenker, M. Kasprzak, H. Saudan, and A. Weis, “A room temperature 19-channel magnetic field mapping device for cardiac signals,” Appl. Phys. Lett. 95(17), 173701 (2009).
[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(8), 904–909 (2003).
[Crossref] [PubMed]

G. Bison, R. Wynands, and A. Weis, “A laser-pumped magnetometer for the mapping of human cardiomagnetic fields,” Appl. Phys. B 76(3), 325–328 (2003).
[Crossref]

Weisend, M.

C. N. Johnson, P. D. D. Schwindt, and M. Weisend, “Multi-sensor magnetoencephalography with atomic magnetometers,” Phys. Med. Biol. 58(17), 6065–6077 (2013).
[Crossref] [PubMed]

C. Johnson, P. D. D. Schwindt, and M. Weisend, “Magnetoencephalography with a two-color pump-probe, fiber-coupled atomic magnetometer,” Appl. Phys. Lett. 97(24), 243703 (2010).
[Crossref]

Wiekhorst, F.

S. Knappe, T. H. Sander, O. Kosch, F. Wiekhorst, J. Kitching, and L. Trahms, “Cross-validation of microfabricated atomic magnetometers with superconducting quantum interference devices for biomagnetic applications,” Appl. Phys. Lett. 97(13), 133703 (2010).
[Crossref]

Wyllie, R.

R. Wyllie, M. Kauer, G. S. Smetana, R. T. Wakai, and T. G. Walker, “Magnetocardiography with a modular spin-exchange relaxation-free atomic magnetometer array,” Phys. Med. Biol. 57(9), 2619–2632 (2012).
[Crossref] [PubMed]

R. Wyllie, M. Kauer, R. T. Wakai, and T. G. Walker, “Optical magnetometer array for fetal magnetocardiography,” Opt. Lett. 37(12), 2247–2249 (2012).
[Crossref] [PubMed]

Wynands, R.

G. Bison, R. Wynands, and A. Weis, “Dynamical mapping of the human cardiomagnetic field with a room-temperature, laser-optical sensor,” Opt. Express 11(8), 904–909 (2003).
[Crossref] [PubMed]

G. Bison, R. Wynands, and A. Weis, “A laser-pumped magnetometer for the mapping of human cardiomagnetic fields,” Appl. Phys. B 76(3), 325–328 (2003).
[Crossref]

Xia, H.

K. Kim, S. Begus, H. Xia, S. K. Lee, V. Jazbinsek, Z. Trontelj, and M. V. Romalis, “Multi-channel atomic magnetometer for magnetoencephalography: a configuration study,” Neuroimage 89, 143–151 (2014).
[Crossref] [PubMed]

H. Xia, A. Ben-Amar Baranga, D. Hoffman, and M. V. Romalis, “Magnetoencephalography with an atomic magnetometer,” Appl. Phys. Lett. 89(21), 211104 (2006).
[Crossref]

Young, A. R.

S. Appelt, A. B.-A. Baranga, C. J. Erickson, M. V. Romalis, A. R. Young, and W. Happer, “Theory of spin-exchange optical pumping of 3He and 129Xe,” Phys. Rev. A 58(2), 1412–1439 (1998).
[Crossref]

Adv. Cardiol. (1)

M. N. Livanov, A. N. Koslov, S. E. Sinelnikova, J. A. Kholodov, V. P. Markin, A. M. Gorbach, and A. V. Korinewsky, “Record of the human magnetocardiogram by the quantum gradiometer with optical pumping,” Adv. Cardiol. 28, 78–80 (1981).
[Crossref] [PubMed]

AIP Adv. (1)

N. Mizutani, K. Okano, K. Ban, S. Ichihara, A. Terao, and T. Kobayashi, “A plateau in the sensitivity of a compact optically pumped atomic magnetometer,” AIP Adv. 4(5), 057132 (2014).
[Crossref]

Appl. Phys. B (1)

G. Bison, R. Wynands, and A. Weis, “A laser-pumped magnetometer for the mapping of human cardiomagnetic fields,” Appl. Phys. B 76(3), 325–328 (2003).
[Crossref]

Appl. Phys. Lett. (6)

G. Bison, N. Castagna, A. Hofer, P. Knowles, J. L. Schenker, M. Kasprzak, H. Saudan, and A. Weis, “A room temperature 19-channel magnetic field mapping device for cardiac signals,” Appl. Phys. Lett. 95(17), 173701 (2009).
[Crossref]

C. Johnson, P. D. D. Schwindt, and M. Weisend, “Magnetoencephalography with a two-color pump-probe, fiber-coupled atomic magnetometer,” Appl. Phys. Lett. 97(24), 243703 (2010).
[Crossref]

S. Knappe, T. H. Sander, O. Kosch, F. Wiekhorst, J. Kitching, and L. Trahms, “Cross-validation of microfabricated atomic magnetometers with superconducting quantum interference devices for biomagnetic applications,” Appl. Phys. Lett. 97(13), 133703 (2010).
[Crossref]

H. Xia, A. Ben-Amar Baranga, D. Hoffman, and M. V. Romalis, “Magnetoencephalography with an atomic magnetometer,” Appl. Phys. Lett. 89(21), 211104 (2006).
[Crossref]

H. B. Dang, A. C. Maloof, and M. V. Romalis, “Ultrahigh sensitivity magnetic field and magnetization measurements with an atomic magnetometer,” Appl. Phys. Lett. 97(15), 151110 (2010).
[Crossref]

T. W. Kornack, S. J. Smullin, S. K. Lee, and M. V. Romalis, “A low-noise ferrite magnetic shield,” Appl. Phys. Lett. 90(22), 223501 (2007).
[Crossref]

Biomed. Opt. Express (2)

Brain Topogr. (1)

S. Taulu, M. Kajola, and J. Simola, “Suppression of Interference and Artifacts by the Signal Space Separation Method,” Brain Topogr. 16(4), 269–275 (2004).
[Crossref] [PubMed]

IEEE Trans. Instrum. Meas. (1)

K. Kim, W.-K. Lee, I.-S. Kim, and H. S. Moon, “Atomic vector gradiometer system using cesium vapor cells for magnetocardiography: perspective on practical application,” IEEE Trans. Instrum. Meas. 56(2), 458–462 (2007).
[Crossref]

J. Electrocardiol. (1)

H. Koch, “Recent advances in magnetocardiography,” J. Electrocardiol. 37(Suppl), 117–122 (2004).
[Crossref] [PubMed]

J. Neurosci. (1)

O. Alem, A. M. Benison, D. S. Barth, J. Kitching, and S. Knappe, “Magnetoencephalography of epilepsy with a microfabricated atomic magnetrode,” J. Neurosci. 34(43), 14324–14327 (2014).
[Crossref] [PubMed]

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

Kardiologiia (1)

I. O. Fomin, S. E. Sinel’nikova, A. N. Kozlov, V. N. Uranov, and V. A. Gorshkov, “Registration of the heart’s magnetic field,” Kardiologiia 23(10), 66–68 (1983).
[PubMed]

Med. Biol. Eng. Comput. (1)

M. A. Uusitalo and R. J. Ilmoniemi, “Signal-space projection method for separating MEG or EEG into components,” Med. Biol. Eng. Comput. 35(2), 135–140 (1997).
[Crossref] [PubMed]

Nature (1)

I. K. Kominis, T. W. Kornack, J. C. Allred, and M. V. Romalis, “A subfemtotesla multichannel atomic magnetometer,” Nature 422(6932), 596–599 (2003).
[Crossref] [PubMed]

Neuroimage (1)

K. Kim, S. Begus, H. Xia, S. K. Lee, V. Jazbinsek, Z. Trontelj, and M. V. Romalis, “Multi-channel atomic magnetometer for magnetoencephalography: a configuration study,” Neuroimage 89, 143–151 (2014).
[Crossref] [PubMed]

Opt. Express (1)

Opt. Lett. (1)

Phys. Med. Biol. (4)

O. Alem, T. H. Sander, R. Mhaskar, J. LeBlanc, H. Eswaran, U. Steinhoff, Y. Okada, J. Kitching, L. Trahms, and S. Knappe, “Fetal magnetocardiography measurements with an array of microfabricated optically pumped magnetometers,” Phys. Med. Biol. 60(12), 4797–4811 (2015).
[Crossref] [PubMed]

C. N. Johnson, P. D. D. Schwindt, and M. Weisend, “Multi-sensor magnetoencephalography with atomic magnetometers,” Phys. Med. Biol. 58(17), 6065–6077 (2013).
[Crossref] [PubMed]

R. Wyllie, M. Kauer, G. S. Smetana, R. T. Wakai, and T. G. Walker, “Magnetocardiography with a modular spin-exchange relaxation-free atomic magnetometer array,” Phys. Med. Biol. 57(9), 2619–2632 (2012).
[Crossref] [PubMed]

V. K. Shah and R. T. Wakai, “A compact, high performance atomic magnetometer for biomedical applications,” Phys. Med. Biol. 58(22), 8153–8161 (2013).
[Crossref] [PubMed]

Phys. Rev. A (8)

M. P. Ledbetter, I. M. Savukov, V. M. Acosta, D. Budker, and M. V. Romalis, “Spin-exchange-relaxation-free magnetometry with Cs vapor,” Phys. Rev. A 77(3), 033408 (2008).
[Crossref]

I. M. Savukov and M. V. Romalis, “Effects of spin-exchange collisions in a high-density alkali-metal vapor in low magnetic fields,” Phys. Rev. A 71(2), 023405 (2005).
[Crossref]

M. A. Rosenberry, J. P. Reyes, D. Tupa, and T. J. Gay, “Radiation trapping in rubidium optical pumping at low buffer-gas pressures,” Phys. Rev. A 75(2), 023401 (2007).
[Crossref]

C. Cohen-Tannoudji and J. Dupont-Roc, “Experimental study of Zeeman light shifts in weak magnetic fields,” Phys. Rev. A 5(2), 968–984 (1972).
[Crossref]

M. Rosatzin, D. Suter, and J. Mlynek, “Light-shift-induced spin echoes in a J=1/2 atomic ground state,” Phys. Rev. A 42(3), 1839–1841 (1990).
[Crossref] [PubMed]

F. Gong, Y. Y. Jau, and W. Happer, “Magnetic resonance reversals in optically pumped alkali-metal vapor,” Phys. Rev. A 75(5), 053415 (2007).
[Crossref]

S. Appelt, A. B.-A. Baranga, C. J. Erickson, M. V. Romalis, A. R. Young, and W. Happer, “Theory of spin-exchange optical pumping of 3He and 129Xe,” Phys. Rev. A 58(2), 1412–1439 (1998).
[Crossref]

B. Chann, E. Babcock, L. W. Anderson, and T. G. Walker, “Skew light propagation in optically thick optical pumping cells,” Phys. Rev. A 66(3), 033406 (2002).
[Crossref]

Phys. Rev. Lett. (1)

J. C. Allred, R. N. Lyman, T. W. Kornack, and M. V. Romalis, “High-Sensitivity Atomic Magnetometer Unaffected by Spin-Exchange Relaxation,” Phys. Rev. Lett. 89(13), 130801 (2002).
[Crossref] [PubMed]

Physiol. Meas. (1)

K. Kamada, Y. Ito, and T. Kobayashi, “Human MCG measurements with a high-sensitivity potassium atomic magnetometer,” Physiol. Meas. 33(6), 1063–1071 (2012).
[Crossref] [PubMed]

Rev. Mod. Phys. (1)

M. Hämäläinen, R. Hari, R. J. Ilmoniemi, J. Knuutila, and O. V. Lounasmaa, “Magnetoencephalography—theory, instrumentation, and applications to noninvasive studies of the working human brain,” Rev. Mod. Phys. 65(2), 413–497 (1993).
[Crossref]

Supercond. Sci. Technol. (1)

K. Sternickel and A. I. Braginski, “Biomagnetism using SQUIDs: status and perspectives,” Supercond. Sci. Technol. 19(3), S160–S171 (2006).
[Crossref]

Other (4)

J. Vrba, J. Nenonen, and L. Trahms, “Biomagnetism,” in The SQUID Handbook (Wiley-VCH, 2006), pp. 269–389.

S. Knappe, T. Sander, and L. Trahms, “Optically-Pumped Magnetometers for MEG,” in Magnetoencephalography, S. Supek and C. J. Aine, eds. (Springer Berlin Heidelberg, 2014), pp. 993–999.

E. A. Lima, A. Irimia, and J. P. Wikswo, “The Magnetic Inverse Problem,” in The SQUID Handbook (Wiley-VCH Verlag, 2006), pp. 139–267.

C. Johnson and P. D. D. Schwindt, “A two-color pump probe atomic magnetometer for magnetoencephalography,” Proc. IEEE Int. Freq. Cont., 371–375 (2010).
[Crossref]

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Figures (8)

Fig. 1
Fig. 1

(a) Schematic of OPM sensor module, top view. Light enters the module from a polarization-maintaining (PM) optical fiber, is split into four beams in a passive diffractive optical element, and is then collimated before entering the Rb vapor cell. Light reflects off of the vapor cell, and the 795-nm pump light is rejected before reaching the polarization analyzer. In this top view, only two of the four laser beams are shown. Abbreviations include 4-CH balanced PD: four-channel balanced (subtracted) photodiodes; PBS: polarizing beam splitter cube; λ/2: half wave plate; λ/4: quarter wave plate. The distance from the midpoints of the laser beams long their paths through the vapor cell to the outside of the module casing is 9 mm. The location of the head of a human MEG subject is noted for reference. (b) Calculated laser beam profiles through the vapor cell. The separation of adjacent spots is 18 mm. The numbers label the magnetometer channels as viewed from the fiber input side of the module.

Fig. 2
Fig. 2

Sensor module with the top casing removed. Blackout material, which obscures the receiving optics, minimizes optical crosstalk and terminates stray reflections within the module. The optical fiber in the input optical assembly is terminated with a glass ferrule for its nonmagnetic properties. The Kevlar thread across the module is used to actuate the half wave plate on the detection arm while the sensor is sealed and in operation. The collimating lens is obscured by its holder and is not directly visible in the picture. The oven has coils, which are printed on flex circuit material, wrapped around its perimeter. These coils may supply both magnetic field modulation and control, although they are not used for the measurements shown below.

Fig. 3
Fig. 3

The slope of the lock-in amplifier output (black squares, left vertical axis) and the longitudinal magnetic field applied to cancel the light shift due to the pump laser (red circles, right vertical axis) are plotted as a function of pump laser detuning from the zero light-shift point. The nitrogen buffer gas in the vapor cell causes the displacement and asymmetry of the lock-in amplifier output relative to zero detuning.

Fig. 4
Fig. 4

(a) The zero-field magnetic resonance is observed when the transverse magnetic field is swept about zero. The red and cyan traces are the subtracted photodiode output of channel 4 converted to the angle of probe laser polarization. The cyan trace is the signal when no 1-kHz modulation is applied. The red trace is the signal when the modulation is applied parallel to the sweeping magnetic field. The black dashed line overlaying the cyan line is the calculated atomic spin polarization. The blue line is the output of the lock-in amplifier. (b) Contour plots of the calculated atomic polarization for a single laser beam passing through the vapor cell. The pump light enters from the left and is reflected at the right to pass through the cell a second time. The top plot is for no transverse field, and the bottom is for 10 nT. Note that the two cases have different color scales.

Fig. 5
Fig. 5

The sensitivity, or rms magnetic noise density, of the four magnetometer channels as a function of measurement frequency. Data for all channels was taken simultaneously. The sensitivities of the four channels are nearly identical. The noise floor is consistent with that previously measured of the same magnetic shield [27].

Fig. 6
Fig. 6

The normalized response of the amplitude of the magnetometers is plotted as a function of applied frequency. The frequency responses of the four magnetometer channels are very similar. Also plotted is the frequency response of the gradiometer formed between channels 1 and 2.

Fig. 7
Fig. 7

(a) Equivalent single-channel sensitivities are determined through synthetic gradiometer measurements. For the Ch 1 − Ch 2 gradiometer (black trace) and for the Ch 3 − Ch 4 gradiometer (blue trace), the inferred single-channel sensitivity is 3–4 fT/Hz1/2 between 10 and 100 Hz. Unlike in the magnetometer case, the loss of sensitivity above ~90 Hz, due to the limited bandwidth, is clearly observable. (b) The subtracted photodiode output for each magnetometer channel. With the magnetometer operating at zero field, the second harmonic of the 1-kHz modulation is mainly observed. The dc offsets among the four channels are caused by the angular dependence of the polarizing beamsplitter. The large dc offset between channel 2 (red trace) and channel 4 (blue trace) is responsible for the worst gradiometer performance of the green trace in (a).

Fig. 8
Fig. 8

The detailed performance of (a) magnetometer channel 4 and (b) the Ch 3 − Ch 4 gradiometer. To illustrate the contributions of different noise sources to the magnetometer, optical and electronic noise sources are plotted with the total magnetic noise. The sensitivity of the Ch 3 − Ch 4 gradiometer above ~10 Hz is limited primarily by the photon shot noise.

Equations (5)

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P t = γ q P×B,
P z = P 0 Δ B 2 B y 2 +Δ B 2
P x = P 0 B y ΔB B y 2 +Δ B 2
ΔB= Γ γ .
1 ( 1+ ( 2π τ LI f ) 2 ) 2 1+ ( f f 3dB ) 2 ,

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