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A high-sensitivity tunable two-beam fiber-coupled high-density magnetometer with laser heating

Sensors (Switzerland) (2016) 16(10)
DOI: 10.3390/s16101691
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Abstract

Atomic magnetometers (AM) are finding many applications in biomagnetism, national security, industry, and science. Fiber-coupled (FC) designs promise to make them compact and flexible for operation. Most FC designs are based on a single-beam configuration or electrical heating. Here, we demonstrate a two-beam FC AM with laser heating that has 5 fT/Hz1/2 sensitivity at low frequency (50 Hz), which is higher than that of other fiber-coupled magnetometers and can be improved to the sub-femtotesla level. This magnetometer is widely tunable from DC to very high frequencies (as high as 100 MHz; the only issue might be the application of a suitable uniform and stable bias field) with a sensitivity under 10 fT/Hz1/2 and can be used for magneto-encephalography (MEG), magneto-cardiography (MCG), underground communication, ultra-low MRI/NMR, NQR detection, and other applications.

Figures

  • Figure 1. Diagram f fi er-coupled AM with laser heating: L—Heating Laser, PrL—Probe Laser, PuL—Pump Laser, DA—Differential Amplifier, SA—Spectrum Analyzer, CS—Current Source, CI—computer interface.
  • Figure 2. (a) The frequency profile of the AM response fit with Expression (2); (b) The sensitivity of the AM when it is tuned to 50 Hz with a bias field; the frequency response (a) is used to convert AM noise spectrum to sensitivity.
  • Figure 3. (a) The frequency profile of the width (spin-exchange part only, ΓSE) using the prediction of the derived here vector-statistical model Equation (6) (P = 0, 0.5, 0.9) and analytical expression for P = 0 [26], which at small bias field can be approximated with a parabola [15]; (b) Comparison of a vector-statistical model and well controlled experimental measurements [25] for magnetic resonance width (this includes spin destruction contributions, Equation (7)) as the function of the bias field for different polarizations. Excellent agreement can be observed between the vector-statistical model and the experimental data. This model also reproduces results for the case of a large magnetic field and a high polarization: 2πΓSE = RSE (1− P) /5 derived for the radio-frequency (RF) magnetometer and used for finding the optimal pumping rate when the pumping rate term is added: Γ = RSE RSD5R + R/4 [27].
  • Figure 4. (a) The optimal pumping rate for different frequencies which maximizes the atomic magnetometer response and hence sensitivity limited by probe laser noise; (b) the magnetic resonance width (bandwidth of the magnetometer) for different frequencies to which bias field is tuned for the optimal pump rate given in (a); (c) the sensitivity coefficient which is the inverse of the AM response (proportional to ∝ ( ) in Equation (1), where q and Γ are functions of frequency and optimal pumping rate, while the optimal pumping rate is also the function of frequency) to an oscillating field at the center of the magnetic resonance when the bias field is applied and the pump rate is optimized to maximize the response for frequencies in 50 Hz incremental steps; it is normalized to unity at 50 Hz; the fitted polynomial curve ( ) = 0.843 +0.0036 + 5.96 × 10 − 1.55 × 10 for the sensitivity coefficient interpolates the data between the calculated points; (d) Sensitivity of AM (red curve) in 0–400 Hz range after multiplying the raw noise calibrated at 50 Hz (black curve) by the AM sensitivity coefficient, accounting for the width and polarization level variation with bias field and optimal pumping rate.

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APA

Savukov, I., & Boshier, M. G. (2016). A high-sensitivity tunable two-beam fiber-coupled high-density magnetometer with laser heating. Sensors (Switzerland), 16(10). https://doi.org/10.3390/s16101691

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